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1.
The C4 photosynthesis carbon-concentrating mechanism in maize (Zea mays) has two CO2 delivery pathways to the bundle sheath (BS; via malate or aspartate), and rates of phosphoglyceric acid reduction, starch synthesis, and phosphoenolpyruvate regeneration also vary between BS and mesophyll (M) cells. The theoretical partitioning of ATP supply between M and BS cells was derived for these metabolic activities from simulated profiles of light penetration across a leaf, with a potential 3-fold difference in the fraction of ATP produced in the BS relative to M (from 0.29 to 0.96). A steady-state metabolic model was tested using varying light quality to differentially stimulate M or BS photosystems. CO2 uptake, ATP production rate (JATP; derived with a low oxygen/chlorophyll fluorescence method), and carbon isotope discrimination were measured on plants under a low light intensity, which is considered to affect C4 operating efficiency. The light quality treatments did not change the empirical ATP cost of gross CO2 assimilation (JATP/GA). Using the metabolic model, measured JATP/GA was compared with the predicted ATP demand as metabolic functions were varied between M and BS. Transamination and the two decarboxylase systems (NADP-malic enzyme and phosphoenolpyruvate carboxykinase) were critical for matching ATP and reduced NADP demand in BS and M when light capture was varied under contrasting light qualities.Interest in the C4 pathway has been increased by the potential for enhancing crop productivity and maintaining yield stability in the face of global warming and population pressure (Friso et al., 2010; Zhu et al., 2010; Covshoff and Hibberd, 2012). Maize (Zea mays), a C4 plant of the NADP-malic enzyme (ME) subtype, is a leading grain production cereal (www.fao.org). C4 photosynthesis is a shared activity between mesophyll (M; abbreviations are listed in BS) cells, coupled to allow the operation of a biochemical carbon-concentrating mechanism (CCM). The CCM effectively minimizes photorespiration by increasing the CO2 concentration in the bundle sheath (CBS), where Rubisco is exclusively expressed. Since BS and M are connected by plasmodesmata, some CO2 retrodiffuses. The refixation of that escaping CO2 by the CCM increases the activity of the CCM and the total ATP demand (ATPBS + ATPM) for gross CO2 assimilation (GA; [ATPBS + ATPM]/GA), from a theoretical minimum of five ATPs (Furbank et al., 1990). Leakiness (Φ), the amount of CO2 retrodiffusing relative to phosphoenolpyruvate (PEP) carboxylation rate, is therefore a proxy for the coordination between the CCM and assimilatory activity (Henderson et al., 1992; Tazoe et al., 2008; Kromdijk et al., 2010; Ubierna et al., 2011; Bellasio and Griffiths, 2013).
Open in a separate windowRecently, the maize C4 subgroup has been shown to be complicated by the presence of two BS decarboxylation enzyme systems (NADP-ME and phosphoenolpyruvate carboxykinase [PEPCK]), presumably both acting as CO2 delivery pathways (via malate [MAL] and Asp, respectively; Furumoto et al., 1999, 2000; Wingler et al., 1999; Eprintsev et al., 2011; Furbank, 2011; Pick et al., 2011). There is also an extensive overlap between BS and M functions, since both cell types can synthesize starch (Spilatro and Preiss, 1987; Kanai and Edwards, 1999) and reduce phosphoglyceric acid (PGA; Majeran and van Wijk, 2009; see the overall scheme in Fig. 1). Additionally, energetic partitioning can also vary between cell types, since the total ATP produced (JATP) per CO2 fixed in GA (JATP/GA) may be produced in BS (mainly through cyclic electron flow [CEF] around PSI) or in M (mainly through linear electron flow [LEF]), depending on the light locally available in BS or M (Kramer and Evans, 2011; Yin and Struik, 2012). Furthermore, although all NADPH is produced in M, the only compartment operating linear electron transport and oxidizing water, some NADPH is exported to BS through MAL diffusion, to meet the reducing power demand therein (NADPHBS). To capture the complex C4 physiology, several models of C4 photosynthesis have been developed (Berry and Farquhar, 1978; Laisk and Edwards, 2000, 2009; von Caemmerer, 2000). The earlier approaches were developed into the von Caemmerer (2000) C4 model. In particular, the associated light-limited equations (referred to subsequently as the “C4 model”) are used to estimate the parameters needed to resolve the isotopic discrimination (Δ) model, widely employed to study Φ under low-light conditions (for review, see Ubierna et al., 2011). The C4 model partitions JATP into two fractions: (1) the ATP consumed by PEP carboxylase, and (2) the ATP consumed by the C3 activity (glyoxylate recycling, PGA reduction [PR], and ribulose 1,5-bisphosphate [RuBP] regeneration). These activities are located in M, BS, or both compartments (see the overall scheme in Fig. 1). However, the C4 model simplifies the spatial compartmentalization between BS and M, and in this paper, we now develop the energetic implications of the differential contribution of M and BS to C4 photosynthesis under different light regimes.Open in a separate windowFigure 1.Metabolic model of C4 assimilation, rates of reaction, and net fluxes between BS and M. The overall scheme reports the reactions of the CCM (Furbank, 2011), Rubisco carboxylation, the reactions of the RPP pathway, the synthesis of starch, respiration, and glyoxylate recycling reactions. The tables, with the corresponding enzyme names, show the actual reaction rates, expressed relative to GA (5.13 μmol m−2 s−1), per unit of substrate transformed. Rates were estimated by parameterizing the model equations (PAR = 125 μE m−2 s−1 (A = 3.96 μmol m−2 s−1; RLIGHT = 1.17 μmol m−2 s−1; JATP = 28.6 μmol m−2 s−1), the output of the C4 model (VC = 5.35 μmol m−2 s−1; VP = 5.89 μmol m−2 s−1; VO = 0.44 μmol m−2 s−1), and the output of the Δ model (Φ = 0.23) under three characteristic ratios of ATP partitionings. These were numbered 1, 2, and 3. Condition 1 corresponds to the lowest ATP available in BS (ATP partitioning similar to that under blue light; Fig. 4B), condition 2 corresponds to an intermediate ATP availability in BS (ATP partitioning equal to that under red light; Fig. 4B), and condition 3 corresponds to the highest ATP available in BS (ATP partitioning equal to that under green light; Fig. 4B). The inset shows net metabolite fluxes between M and BS in multiples of GA. The ATP demand in BS (ATPBS) and M (ATPM), the total NADPH demand (NADPHTOT), and the NADPHBS were also calculated in the same three relevant conditions. PYR, Pyruvic acid.Because of these anatomical, metabolic, and energetic complexities, C4 metabolism is highly sensitive to limiting light intensity (Bellasio and Griffiths, 2013) and, potentially, light quality (Evans et al., 2007). Light quality has a greater influence on C4 photosynthesis than on C3. Leaf pigments preferentially absorb the blue and red region of the spectra, and some wavelengths penetrate deeper into leaves. It was shown in C3 leaves that exposure to different wavelengths results in characteristic light penetration profiles, which, translated into different gradients in PSII yield, rates of ATP production, and assimilation (A) within the leaf (Terashima et al., 2009). In C4 leaves, because of the concentric anatomy, light reaches M cells before the deeper BS (Evans et al., 2007) and could alter the balance between light harvesting and energetic partitioning between BS and M.In this paper, we model the likely profiles of light penetration for specific wavelengths associated with red, green, and blue light within a maize M and BS leaf cross section and calculate the impact on potential ATP production for each cell type. We calculate the proportion of absorbed light (AB) for each wavelength, expressed as AB BS/M, the fraction of photons absorbed in BS relative to the photons absorbed in M, from which we derive JATPBS/JATPM, the fraction of ATP produced in BS relative to the ATP produced in M. Second, we developed a steady-state metabolic model (Fig. 1; von Caemmerer 2000), to capture the spatial separation between BS and M and partitions the ATP demand between BS and M cells in terms of PR, starch synthesis (SS), and PEP regeneration, so as to meet the ATP availability in each cell type (Evans et al., 2007). Third, photosynthetic characteristics (leaf-level ATP production rate, CO2 assimilation, stomatal conductance, and Φ derived from online carbon isotope discrimination [Δ]) were measured under red, green, and blue light, and red, green, and blue light in combination (RGB), using a decreasing photon flux density (from 500 to 50 μE m−2 s−1) to investigate the importance of metabolic plasticity under limiting light intensities.
Open in a separate windowFor instance, AB BS/M and JATPBS/JATPM were both lower under the blue light (wavelength 460 nm), which is rapidly extinguished within the M leaf profile, than under white light, confirming that light quality perturbs C4 energetics. In spite of this shift, when maize plants were exposed to different light qualities, there was no change in Φ, indicating that, at steady state, the coordination between CCM activity and Rubisco assimilation was retained (Ubierna et al., 2011; Sun et al., 2012). The modeled metabolic plasticity projected a window for ATP demand partitioning (ATPBS/ATPM), which matched the values for JATPBS/JATPM supply estimated under red, green, and blue light. We show that the plasticity of C4 metabolism, and in particular the possibility of shifting between MAL and Asp as a primary carboxylase product, was of pivotal importance in allowing the plasticity of ATP and NADPH demand. In conclusion, our study explains the extensive overlap between BS and M functions and the requirement for at least two decarboxylase systems in NADP-ME subtype plants such as maize, providing an explanation for empirical observations on the diversity of decarboxylase activities and PEP regeneration pathways (Rathnam, 1978; Chapman and Hatch, 1981; Wingler et al., 1999; Eprintsev et al., 2011; Furbank, 2011; Pick et al., 2011). 相似文献
Table I.
Variables and acronyms described in the textAbbreviation | Definition | Unit |
---|---|---|
A | Net assimilation | μmol m−2 s−1 |
AB | Absorbed light | |
AB BS/M | Partitioning of absorbed light | Dimensionless |
ATPBS | ATP demand in BS | μmol m−2 s−1 |
ATPM | ATP demand in M | μmol m−2 s−1 |
BS | Bundle sheath | |
CBS | CO2 concentration in BS | μmol mol−1 |
CCM | Carbon-concentrating mechanism | |
CEF | Cyclic electron flow | |
DHAP | Dihydroxyacetone phosphate | |
ETR | Electron transport rate | μmol m−2 s−1 |
GA | Gross assimilation (A + RLIGHT) | μmol m−2 s−1 |
gBS | Bundle sheath conductance to CO2, calculated by fitting JMOD to JATP | mol m2 s−1 |
IRGA | Infrared gas analyzer | |
JATP | Total ATP production rate | μmol m−2 s−1 |
JATPBS | ATP production rate in BS | μmol m−2 s−1 |
JATPM | ATP production rate in M | μmol m−2 s−1 |
JMOD | Modeled ATP production rate | μmol m−2 s−1 |
LEF | Linear electron flow | |
LCP | Light compensation point | |
M | Mesophyll | |
MAL | Malate | |
MDH | Malate dehydrogenase | |
MDHBS | Malate dehydrogenase reaction rate in BS | μmol m−2 s−1 |
MDHM | Malate dehydrogenase reaction rate in M | μmol m−2 s−1 |
ME | Malic enzyme | |
ME | Malic enzyme reaction rate | μmol m−2 s−1 |
NADPHBS | NADPH demand in BS | μmol m−2 s−1 |
NADPHTOT | Total NADPH demand | μmol m−2 s−1 |
OAA | Oxaloacetic acid | |
PAR | Photosynthetically active radiation | μE m−2 s−1 |
PEP | Phosphoenolpyruvate | |
PEPCK | Phosphoenolpyruvate carboxykinase | |
PEPCK | PEPCK reaction rate | μmol m−2 s−1 |
PGA | 3-Phosphoglyceric acid | |
PPDK | Pyruvate phosphate dikinase | |
PPDK | PPDK reaction rate | μmol m−2 s−1 |
PR | PGA reduction | |
PRBS | PR rate in BS | μmol m−2 s−1 |
PRM | PR rate in M | μmol m−2 s−1 |
RBS | Respiration in the light in BS | μmol m−2 s−1 |
RLIGHT | Respiration in the light | μmol m−2 s−1 |
RPP | Reductive pentose phosphate | |
RuBP | Ribulose-1,5-bisphosphate | |
RuP | Ribulose-5-phosphate | |
SS | Starch synthesis | |
SSBS | Starch synthesis rate in BS | μmol m−2 s−1 |
SSM | Starch synthesis rate in M | μmol m−2 s−1 |
SSTOT | Total starch synthesis rate | μmol m−2 s−1 |
T | Transamination rate | μmol m−2 s−1 |
VC | Rubisco carboxylation rate | μmol m−2 s−1 |
VO | Rubisco oxygenation rate | μmol m−2 s−1 |
VP | PEP carboxylation rate | μmol m−2 s−1 |
Y(II) | Yield of PSII | |
Δ | 13C isotopic discrimination | ‰ |
δ13C | 13C isotopic composition relative to Pee Dee Belemnite | ‰ |
Φ | Leakiness | Dimensionless |
Table II.
Steady-state equations for the metabolic model of C4 assimilationProcesses described by Equations 4 to 10 can be calculated directly from the measured data for A, RLIGHT, and the output of the von Caemmerer C4 model (VO, VP, and VC), while Equations 11 to 21 require prior allocation of SS, PR, and PEPCK. For simplicity, enzyme names in italics represent the enzyme reaction rate. For stoichiometric consistency, reaction rates are calculated as rates of substrate transformation.Process | Symbol | Reaction Rate | Equation | Localization | Notes |
---|---|---|---|---|---|
Gross assimilation | GA | (4) | GA and RLIGHT rates are expressed per CO2. | ||
RuP phosphorylation | – | (5) | BS | RuP phosphorylation supplies Rubisco carboxylating activity (VC) together with oxygenating activity (VO). | |
Total PR | PRTOT | (6) | BS and M | This equation calculates the total rate of PR on the basis of the PGA produced by Rubisco carboxylation (2VC), Rubisco oxygenation (VO), and glyoxylate recycling (0.5VO) and considers the PGA consumed by respiration; 1/3 is the stoichiometric conversion between respiration (expressed per CO2) and PR (expressed per triose). | |
Total NADPH demand | NADPHTOT | (7) | BS and M | PR consumes one NADPH per PGA; the total rate of PR is PRTOT (see note to Eq. 6); in glyoxylate regeneration (per glyoxylate), 0.5 NADH is produced by Gly decarboxylase, 0.5 NADH is consumed by hydroxypyruvate reductase, and one ferredoxin (equivalent to 0.5 NADPH) is consumed by Gln synthetase; in total, 0.5 NADPH is consumed per glyoxylate (equivalent to VO rate; Supplemental Table S1; Yoshimura et al., 2004). | |
DHAP entering RPP | – | (8) | BS | The DHAP entering the RPP pathway corresponds to the total PR rate minus the DHAP used for starch synthesis, which in this work is expressed per triose. | |
Total SS | SSTOT | (9) | BS and M | In this model, assimilation is entirely converted to starch; this assumption does not influence energetics, as starch synthesis has the same ATP demand as phloem-loaded Suc; in Equation 9, 1/3 converts the stoichiometry of A (expressed per CO2) to the stoichiometry of SS (expressed per triose). | |
Total PEP regeneration | – | (10) | BS and M | PEP regeneration rate equals PEP consumption rate VP at steady state; PEP can be regenerated either by PPDK (mainly in M but active also in BS) or by PEPCK in BS; in this study, PPDK activity was assumed to be zero in BS. | |
Total ATP demand | ATPBS + ATPM | (11) | BS and M | Equation 11 calculates the total ATP demand as the sum of ATP demand for PR (one ATP per PGA, corresponding to PR), RuBP regeneration (one ATP per RuP, corresponding to VC + VO), glyoxylate recycling (one ATP per glyoxylate, corresponding to VO), starch synthesis (0.5 ATP per triose, corresponding to SS), and PEP regeneration (one ATP per PEPCK catalytic event or two ATP per PPDK catalytic event); compared with the original formulation of the C4 model, Equation 11 separates the ATP demand for PEPCK and PPDK, includes the ATP demand for SS, and considers the PGA utilized by respiration, which does not need to be reduced (see Eq. 6). | |
ATP demand in BS | ATPBS | (12) | BS | The ATP demand in BS is brought about by PR (at the rate of PRBS), RuBP regeneration (at the rate of VC + VO), glyoxylate recycling (at the rate of VO), starch synthesis (0.5 ATP per triose), and PEPCK activity (one ATP per OAA; see note to Eq. 11). | |
ATP demand in M | ATPM | (13) | M | The ATP demand in M is brought about by PR (at the rate of PRM), SS, and PPDK (two ATPs per pyruvic acid; see note to Eq. 11). | |
NADPH demand in BS | NADPHBS | (14) | BS | The NADPH demand in BS is brought about by PR (one NADPH per PGA) and glyoxylate recycling, which consumes 0.5 NADPH per glyoxylate (corresponding to VO; see Supplemental Table S2). | |
NADPH supply to BS | – | MDHM | (15) | BS | All NADPH available in BS is produced in M and exported through the MAL shuttle because we have assumed that no linear electron transport (i.e. water oxidation) occurred in BS; for this reason, the NADPH supply to BS corresponds to the NADPH consumed to reduce OAA to MAL in M, the process responsible for NADPH export, and not to the rate of MAL decarboxylation in BS, which depends on T, PEPCK, and MDHBS (Eq. 19). |
MDH activity in M | MDHM | (16) | M | MDH activity supplies the NADPH demand in BS; Equation 16 was derived from Equations 14 and 15. | |
Transamination | T | (17) | BS and M | Equation 17 expresses that, at steady state, all OAA is either transaminated or reduced; since T bypasses the MDHM reaction, which is the reaction responsible for NADPH export to BS (see note to Eq. 15), T has the function of balancing NADPH supply and demand, which becomes apparent when Equations 15 and 17 are combined. | |
MDH | MDHBS | T − PEPCK | (18) | BS | MDH is assumed to operate a fast conversion at equilibrium; therefore, it is passively regulated by the substrate availability: the OAA that is not used by PEPCK is reduced to MAL by MDH; MDH may use NADH, since no NADPH-dependent reduction of OAA has been observed in maize (Kanai and Edwards, 1999) and it is likely mitochondrial (Rathnam, 1978; Chapman and Hatch, 1981); the NADH regeneration may be carried out by chloroplastic ME, which is reported to react both with NADP and NAD (Chapman and Hatch, 1981); however, the process may be more complicated (Eprintsev et al., 2011, and refs. therein); note that in this study, we assumed that cells are decompartmentalized while PEPCK rate was manipulated to increase between zero and a maximum rate in response to ATP availability (see “Minimum and Maximum BS Allocation” for details). |
ME | ME | MDHM + MDHBS | 19 | BS | Equation 19 expresses that the rate of MAL oxidation by ME corresponds to the rate of MAL produced by MDH activity in M plus the rate of MAL produced by MDH activity in BS. |
PPDK | PPDK | VP − PEPCK | 20 | M | The PEP regenerated by PEPCK in BS diffuses to M and reduces the requirement of PEP regenerated by PPDK in M. |
PR in M | PRM | PRTOT − PRBS | 21 | M | PR is a shared process between BS and M. |
2.
Root System Markup Language: Toward a Unified Root Architecture Description Language 总被引:1,自引:0,他引:1
Guillaume Lobet Michael P. Pound Julien Diener Christophe Pradal Xavier Draye Christophe Godin Mathieu Javaux Daniel Leitner Félicien Meunier Philippe Nacry Tony P. Pridmore Andrea Schnepf 《Plant physiology》2015,167(3):617-627
3.
Rita Giuliani Nuria Koteyeva Elena Voznesenskaya Marc A. Evans Asaph B. Cousins Gerald E. Edwards 《Plant physiology》2013,162(3):1632-1651
The genus Oryza, which includes rice (Oryza sativa and Oryza glaberrima) and wild relatives, is a useful genus to study leaf properties in order to identify structural features that control CO2 access to chloroplasts, photosynthesis, water use efficiency, and drought tolerance. Traits, 26 structural and 17 functional, associated with photosynthesis and transpiration were quantified on 24 accessions (representatives of 17 species and eight genomes). Hypotheses of associations within, and between, structure, photosynthesis, and transpiration were tested. Two main clusters of positively interrelated leaf traits were identified: in the first cluster were structural features, leaf thickness (Thickleaf), mesophyll (M) cell surface area exposed to intercellular air space per unit of leaf surface area (Smes), and M cell size; a second group included functional traits, net photosynthetic rate, transpiration rate, M conductance to CO2 diffusion (gm), stomatal conductance to gas diffusion (gs), and the gm/gs ratio. While net photosynthetic rate was positively correlated with gm, neither was significantly linked with any individual structural traits. The results suggest that changes in gm depend on covariations of multiple leaf (Smes) and M cell (including cell wall thickness) structural traits. There was an inverse relationship between Thickleaf and transpiration rate and a significant positive association between Thickleaf and leaf transpiration efficiency. Interestingly, high gm together with high gm/gs and a low Smes/gm ratio (M resistance to CO2 diffusion per unit of cell surface area exposed to intercellular air space) appear to be ideal for supporting leaf photosynthesis while preserving water; in addition, thick M cell walls may be beneficial for plant drought tolerance.Leaves have evolved in different environments into a multitude of sizes and shapes, showing great variation in morphology and anatomy (Evans et al., 2004). However, all leaf typologies share common functions associated with chloroplasts, namely to intercept sunlight, take up CO2 and inorganic nitrogen, and perform photosynthesis as a primary process for growth and reproduction.Investigating relationships between leaf anatomy and photosynthetic features (CO2 fixation, which involves physical and biochemical processes and loss of water by transpiration) could lead to the identification of structural features for enhancing crop productivity and improve our understanding of plant evolution and adaptation (Evans et al., 2004).Stomata, through which CO2 and water vapor diffuse into and out of the leaf, are involved in the regulation and control of photosynthetic and transpiration responses (Jarvis and Morison, 1981; Farquhar and Sharkey, 1982). Besides stomata distribution patterns between the abaxial and adaxial lamina surfaces (Foster and Smith, 1986), stomatal density and size are leaf anatomical traits contributing to build the leaf stomatal conductance to gas diffusion (gs). This is calculated as the reciprocal of the stomatal resistances to gas diffusion; stomatal control results in a lower concentration of CO2 in the leaf mesophyll (M) intercellular air space (Ci) than in the atmosphere (Ca; Nobel, 2009).Leaf M architecture greatly contributes to the pattern of light attenuation profiles within the lamina (Terashima and Saeki, 1983; Woolley, 1983; Vogelmann et al., 1989; Evans, 1999; Terashima et al., 2011) and affects CO2 diffusion from the intercellular air space (IAS) to the chloroplast stroma. Therefore, it influences photosynthetic activity (Flexas et al., 2007, 2008) and can have effects on leaf hydrology and transpiration (Sack et al., 2003; Brodribb et al., 2010; Ocheltree et al., 2012). In addition, M architecture sets boundaries for leaf photosynthetic responses to changing environmental conditions (Nobel et al., 1975).Fortunately, several methodologies are currently available (Flexas et al., 2008; Pons et al., 2009) to determine M conductance to CO2 diffusion (gm), expressed per unit of leaf surface area. It is calculated as the reciprocal of the cumulated partial resistances exerted by leaf structural traits and biochemical processes from the substomatal cavities to photosynthetic sites (Evans et al., 2009; Nobel, 2009). The resistance to CO2 diffusion in the liquid phase is 4 orders of magnitude higher than in the gaseous phase (Nobel, 2009); therefore, the changes in CO2 concentration in the leaf gas phase are small in comparison with the changes in the liquid phase (Niinemets, 1999; Aalto and Juurola, 2002; Nobel, 2009). In the liquid phase, the resistance to CO2 transfer is built from contributions by the cell walls, the plasmalemma, cytoplasm, chloroplast membranes, and stroma (Tholen and Zhu, 2011; Tholen et al., 2012); in addition, it involves factors associated with the carboxylation reaction (Kiirats et al., 2002; Evans et al., 2009). Thus, the concentration of CO2 in the chloroplasts (Cc) is lower than Ci and can limit photosynthesis.At steady state, the relationships between the leaf net photosynthetic rate (A), the concentrations of CO2, and the stomatal conductance to CO2 diffusion (gs_CO2) and gm are modeled based on Fick’s first law of diffusion (Nobel, 2009) as:(1)where Ca, Ci, and Cc are as defined above (Flexas et al., 2008).The magnitude of gm has been found to correlate with certain leaf structural traits in some species, in particular with the M cell surface area exposed to IAS per (one side) unit of leaf surface area (Smes) and its extent covered by chloroplasts (Schl; Evans and Loreto, 2000; Slaton and Smith, 2002; Tholen et al., 2012). From a physical modeling perspective, increasing Smes provides more pathways acting in parallel for CO2 diffusion (to and from the chloroplasts) per unit of leaf surface area; thus, it tends to reduce the resistance to CO2 movement into the M cells and to increase gm (Evans et al., 2009; Nobel, 2009). A number of leaf structural traits affect Smes, including leaf thickness, cell density, cell volume and shape, and the fraction of the M cell walls in contact with the IAS (Terashima et al., 2001, 2011), and the degree they are linked to Smes can vary between species (Slaton and Smith, 2002; Terashima et al., 2006). In particular, the presence of lobes on M cells, which are prominent in some Oryza species, may contribute to gm through increasing Smes (Sage and Sage, 2009; Terashima et al., 2011; Tosens et al., 2012). The M cell wall can provide resistance in series for M CO2 diffusion (Nobel, 2009); thicker cell walls may increase resistance to CO2 movement into the M cells and decrease gm (Terashima et al., 2006, 2011; Evans et al., 2009).Other leaf traits, such as M porosity (the fraction of M volume occupied by air spaces [VolIAS]), has been shown to have a positive correlation with gm in some species (Peña-Rojas et al., 2005), but the association may be mediated by light availability (Slaton and Smith, 2002). Leaf thickness (Thickleaf) tends to be negatively linked to gm, and it may set an upper limit for the maximum gm, according to Terashima et al. (2006), Flexas et al. (2008), and Niinemets et al. (2009).With respect to leaf structural traits and water relations, Thickleaf may increase the apoplast path length (resistances in series; Nobel, 2009) in the extra-xylem M (Sack and Holbrook, 2006; Brodribb et al., 2007) for water to reach the evaporation sites, which could decrease the conductance of water through the M and lower the transpiration rate. Interestingly, while thicker M cell walls may reduce gm, they can enable the development of higher water potential gradients between the soil and leaves, which can be decisive for plant survival and longevity under drought conditions (Steppe et al., 2011).The purpose of this study was to provide insight into how the diversity of leaf structure relates to photosynthesis and transpiration among representative cultivated species and wild relatives in the genus Oryza. This includes, in particular, identifying leaf structural features associated with the diffusion of CO2 from the atmosphere to the chloroplasts, photosynthesis, transpiration efficiency (A/E), and drought tolerance. The genus consists of 10 genomic groups and is composed of approximately 24 species (the number depending on taxonomic preferences; Kellogg, 2009; Brar and Singh, 2011), including the cultivated species Oryza sativa and Oryza glaberrima. Oryza species are distributed around the world, and they exhibit a wide range of phenotypes, with annual versus perennial life cycles and sun- versus shade-adapted species (Vaughan, 1994; Vaughan et al., 2008; Brar and Singh, 2011; Jagadish et al., 2011). This diversity in the genus is an important resource, which is being studied to improve rice yield, especially under unfavorable environmental conditions. In particular, O. glaberrima, Oryza australiensis, and Oryza meridionalis are of interest as drought-tolerant species (Henry et al., 2010; Ndjiondjop et al., 2010; Scafaro et al., 2011, 2012), while Oryza coarctata is salt tolerant (Sengupta and Majumder, 2010). In this study, a total of 43 leaf functional and structural parameters were collected on 24 accessions corresponding to 17 species within eight genomes (Brar and Singh (2011). Life cycle is as follows: A = annual; B = biennial; P = poliennial. Habitat is as follows: S = shade; S-Sh = sun-shade.
Open in a separate windowFor evaluating aspects of photosynthesis, the model in Equation 1 was considered, and all the listed functional variables, A, gs_CO2, (Ca − Ci), gm, and (Ci − Cc), were determined. In addition, among the leaf functional traits, the M resistance to CO2 diffusion per unit of cell surface area exposed to IAS (reciprocal of gm/Smes) was calculated as described by Evans et al. (2009): it represents the resistance to CO2 diffusion from IAS to chloroplasts in a liquid solution through cell wall and membranes (Nobel, 2009). Leaf transpiration rate (E), A/E, the intrinsic A/E (ratio between A and stomatal conductance to water vapor diffusion [gs_H2O]), gm/gs_CO2 (representing the coordination between gm and gs), and the carbon isotope composition of leaf biomass (δ13C; calculated as 13C/12C) were determined. The value of δ13C has been recognized as a potential indicator of leaf A/E: increased limitations on photosynthesis by decreased gs can lead to higher A/gs_H2O ratios and less discrimination against assimilation of 13CO2 (for review, see Farquhar et al., 1989); the leaf A/E may also be positively linked to the gm/gs ratio (Flexas et al., 2008, 2013; Barbour et al., 2010). With respect to leaf structure, the stomatal density, stomatal pore length, and indices of stomatal pore area on both lamina sides (according to Sack et al., 2003), the Thickleaf, VolIAS, Smes, Schl, area of M cell section (acell) in leaf cross sections, cell wall thickness (Thickcw), and M cell surface lobing (Lobcell) were the principal traits estimated. A statistical multivariate analysis (Child, 2006) was employed to identify clusters of highly interrelated leaf traits; trait-to-trait correlation analysis was carried out to further examine leaf structural, functional, and structural-functional relationships.The following are the main hypotheses examined in this study. (1) Leaf thickness will be associated with certain M structural features. (2) gm will be coordinated with M structural traits. (3) A will be correlated with gs, gm, and E. (4) Leaf structural traits will be involved in the relationship between A and E, which will affect leaf A/E. (5) The gm/gs ratio will be positively correlated with leaf A/E; associations with high Thickcw could have implications for plant drought tolerance. 相似文献
Genome | Species | Life Cycle | Habitat | Accession | No. |
---|---|---|---|---|---|
AA | O. barthii | A | S | PI 590400* | 1 |
AA | O. glaberrima | A | S | PI 450430* | 2 |
AA | O. glumaepatula | P | S | PI 527362* | 3 |
AA | O. longistaminata | P | S | IRGC 101207* | 4 |
AA | O. longistaminata | P | S | IRGC 101754 | 5 |
AA | O. meridionalis | A/P | S | IRGC 93265* | 6 |
AA | O. nivara | A/B | S | PI 590405* | 7 |
AA | O. rufipogon | P | S | PI 104640 | 8 |
AA | O. rufipogon | S | PI 590421* | 9 | |
AA | O. sativa | A | S | IR64* | 10 |
AA | O. sativa | A | S | IR72 | 11 |
BB | O. punctata | A | S-Sh | IRGC 105690* | 12 |
BBCC | O. minuta | P | S-Sh | IRGC 101141* | 13 |
CC | O. officinalis | P | S-Sh | PI 59412* | 14 |
CC | O. rhizomatis | P | S | IRGC 101609 | 15 |
CC | O. rhizomatis | P | S | IRGC 105950* | 16 |
CCDD | O. alta | P | S-Sh | PI 590398* | 17 |
CCDD | O. latifolia | P | S-Sh | IRGC 100959* | 18 |
CCDD | O. latifolia | P | S-Sh | IRGC 105173 | 19 |
EE | O. australiensis | P | S | IRGC 101397* | 20 |
EE | O. australiensis | P | S | IRGC 105277* | 21 |
EE | O. australiensis | P | S | IRGC 86527 | 22 |
FF | O. brachyantha | B | S | IRGC 101232* | 23 |
HHKK | O. coarctata | P | S | IRGC 104502* | 24 |
4.
5.
Posttranslational modifications (PTMs) of proteins greatly expand proteome diversity, increase functionality, and allow for rapid responses, all at relatively low costs for the cell. PTMs play key roles in plants through their impact on signaling, gene expression, protein stability and interactions, and enzyme kinetics. Following a brief discussion of the experimental and bioinformatics challenges of PTM identification, localization, and quantification (occupancy), a concise overview is provided of the major PTMs and their (potential) functional consequences in plants, with emphasis on plant metabolism. Classic examples that illustrate the regulation of plant metabolic enzymes and pathways by PTMs and their cross talk are summarized. Recent large-scale proteomics studies mapped many PTMs to a wide range of metabolic functions. Unraveling of the PTM code, i.e. a predictive understanding of the (combinatorial) consequences of PTMs, is needed to convert this growing wealth of data into an understanding of plant metabolic regulation.The primary amino acid sequence of proteins is defined by the translated mRNA, often followed by N- or C-terminal cleavages for preprocessing, maturation, and/or activation. Proteins can undergo further reversible or irreversible posttranslational modifications (PTMs) of specific amino acid residues. Proteins are directly responsible for the production of plant metabolites because they act as enzymes or as regulators of enzymes. Ultimately, most proteins in a plant cell can affect plant metabolism (e.g. through effects on plant gene expression, cell fate and development, structural support, transport, etc.). Many metabolic enzymes and their regulators undergo a variety of PTMs, possibly resulting in changes in oligomeric state, stabilization/degradation, and (de)activation (Huber and Hardin, 2004), and PTMs can facilitate the optimization of metabolic flux. However, the direct in vivo consequence of a PTM on a metabolic enzyme or pathway is frequently not very clear, in part because it requires measurements of input and output of the reactions, including flux through the enzyme or pathway. This Update will start out with a short overview on the major PTMs observed for each amino acid residue (PTMs, including determination of the localization within proteins (i.e. the specific residues) and occupancy. Challenges in dealing with multiple PTMs per protein and cross talk between PTMs will be briefly outlined. We then describe the major physiological PTMs observed in plants as well as PTMs that are nonenzymatically induced during sample preparation (PTMs, in particular for enzymes in primary metabolism (Calvin cycle, glycolysis, and respiration) and the C4 shuttle accommodating photosynthesis in C4 plants (PTMs observed in plants
Open in a separate window
Open in a separate window
Open in a separate windowThere are many recent reviews focusing on specific PTMs in plant biology, many of which are cited in this Update. However, the last general review on plant PTMs is from 2010 (Ytterberg and Jensen, 2010); given the enormous progress in PTM research in plants over the last 5 years, a comprehensive overview is overdue. Finally, this Update does not review allosteric regulation by metabolites or other types of metabolic feedback and flux control, even if this is extremely important in the regulation of metabolism and (de)activation of enzymes. Recent reviews for specific pathways, such as isoprenoid metabolism (Kötting et al., 2010; Banerjee and Sharkey, 2014; Rodríguez-Concepción and Boronat, 2015), tetrapyrrole metabolism (Brzezowski et al., 2015), the Calvin-Benson cycle (Michelet et al., 2013), starch metabolism (Kötting et al., 2010; Geigenberger, 2011; Tetlow and Emes, 2014), and photorespiration (Hodges et al., 2013) provide more in-depth discussions of metabolic regulation through various posttranslational mechanisms. Many of the PTMs that have been discovered in the last decade through large-scale proteomics approaches have not yet been integrated in such pathway-specific reviews, because these data are not always easily accessible and because the biological significance of many PTMs is simply not yet understood. We hope that this Update will increase the general awareness of the existence of these PTM data sets, such that their biological significance can be tested and incorporated in metabolic pathways. 相似文献
Amino Acid Residue | Observed Physiological PTM in Plants | PTMs Caused by Sample Preparation |
---|---|---|
Ala (A) | Not known | |
Arg (R) | Methylation, carbonylation | |
Asn (N) | Deamidation, N-linked gycosylation | Deamidation |
Asp (D) | Phosphorylation (in two-component system) | |
Cys (C) | Glutathionylation (SSG), disulfide bonded (S-S), sulfenylation (-SOH), sulfonylation (-SO3H), acylation, lipidation, acetylation, nitrosylation (SNO), methylation, palmitoylation, phosphorylation (rare) | Propionamide |
Glu (E) | Carboxylation, methylation | Pyro-Glu |
Gln (Q) | Deamidation | Deamidation, pyro-Glu |
Gly (G) | N-Myristoylation (N-terminal Gly residue) | |
His (H) | Phosphorylation (infrequent) | Oxidation |
Ile (I) | Not known | |
Leu (L) | Not known | |
Lys (K) | N-ε-Acetylation, methylation, hydroxylation, ubiquitination, sumoylation, deamination, O-glycosylation, carbamylation, carbonylation, formylation | |
Met (M) | (De)formylation, excision (NME), (reversible) oxidation, sulfonation (-SO2), sulfoxation (-SO) | Oxidation, 2-oxidation, formylation, carbamylation |
Phe (F) | Not known | |
Pro (P) | Carbonylation | Oxidation |
Ser (S) | Phosphorylation, O-linked glycosylation, O-linked GlcNAc (O-GlcNAc) | Formylation |
Thr (T) | Phosphorylation, O-linked glycosylation, O-linked GlcNAc (O-GlcNAc), carbonylation | Formylation |
Trp (W) | Glycosylation (C-mannosylation) | Oxidation |
Tyr (Y) | Phosphorylation, nitration | |
Val (V) | Not known | |
Free NH2 of protein N termini | Preprotein processing, Met excision, formylation, pyro-Glu, N-myristoylation, N-acylation (i.e. palmitoylation), N-terminal α-amine acetylation, ubiquitination | Formylation (Met), pyro-Glu (Gln) |
Table II.
Most significant and/or frequent PTMs observed in plantsType of PTM (Reversible, Except if Marked with an Asterisk) | Spontaneous (S; Nonenzymatic) or Enzymatic (E) | Comment on Subcellular Location and Frequency |
---|---|---|
Phosphorylation (Ser, Thr, Tyr, His, Asp) | E | His and Asp phosphorylation have low frequency |
S-Nitrosylation (Cys) and nitration* (Tyr) | S (RNS), but reversal is enzymatic for Cys by thioredoxins | Throughout the cell |
Acetylation (N-terminal α-amine, Lys ε-amine) | E | In mitochondria, very little N-terminal acetylation, but high Lys acetylation; Lys acetylation correlates to [acetyl-CoA] |
Deamidation (Gln, Asn) | S, but reversal of isoAsp is enzymatic by isoAsp methyltransferase | Throughout the cell |
Lipidation (S-acetylation, N-meristoylation*, prenylation*; Cys, Gly, Lys, Trp, N terminal) | E | Not (or rarely) within plastids, mitochondria, peroxisomes |
N-Linked glycosylation (Asp); O linked (Lys, Ser, Thr, Trp) | E | Only proteins passing through the secretory system; O linked in the cell wall |
Ubiquination (Lys, N terminal) | E | Not within plastids, mitochondria, peroxisomes |
Sumoylation (Lys) | E | Not within plastids, mitochondria, peroxisomes |
Carbonylation* (Pro, Lys, Arg, Thr) | S (ROS) | High levels in mitochondria and chloroplast |
Methylation (Arg, Lys, N terminal) | E | Histones (nucleus) and chloroplasts; still underexplored |
Glutathionylation (Cys) | E | High levels in chloroplasts |
Oxidation (Met, Cys) | S (ROS) and E (by PCOs; see Fig. 1B), but reversal is enzymatic by Met sulfoxide reductases, glutaredoxins, and thioredoxins, except if double oxidized | High levels in mitochondria and chloroplast |
Peptidase* (cleavage peptidyl bond) | E | Throughout the cell |
S-Guanylation (Cys) | S (RNS) | Rare; 8-nitro-cGMP is signaling molecule in guard cells |
Formylation (Met) | S, but deformylation is enzymatic by peptide deformylase | All chloroplasts and mitochondria-encoded proteins are synthesized with initiating formylated Met |
Table III.
Regulation by PTMs in plant metabolism and classic examples of well-studied enzymes and pathwaysMany of these enzymes also undergo allosteric regulation through cellular metabolites. GAPDH, Glyceraldehyde-3-phosphate dehydrogenase; PRK, phosphoribulokinase.Process | Enzymes | PTMs, Protein Modifiers, Localization | References |
---|---|---|---|
Calvin-Benson cycle (chloroplasts) | Many enzymes | Oxidoreduction of S-S bonds, reversible nitrosylation, glutathionylation; through ferredoxin/ferredoxin-thioredoxin reductase/thioredoxins (mostly f and m) and glutaredoxins; proteomics studies in Arabidopsis and C. reinhardtii | Michelet et al. (2013) |
Rubisco | Methylation, carbamylation, acetylation, N-terminal processing, oligomerization; classical studies in pea (Pisum sativum), spinach (Spinacia oleracea), and Arabidopsis | Houtz and Portis (2003); Houtz et al. (2008) | |
GAPDH/CP12/PRK supercomplex | Dynamic heterooligomerization through reversible S-S bond formation controlled by thioredoxins | Graciet et al. (2004); Michelet et al. (2013); López-Calcagno et al. (2014) | |
Glycolysis | Cytosolic PEPC | Phosphorylation (S, T), monoubiquitination | O’Leary et al. (2011) |
Photorespiration | Seven enzymes are phosphorylated | Phosphorylation from meta-analysis of public phosphoproteomics data for Arabidopsis; located in chloroplasts, peroxisomes, mitochondria | Hodges et al. (2013) |
Maize glycerate kinase | Redox-regulated S-S bond; thioredoxin f; studied extensively in chloroplasts of C4 maize | Bartsch et al. (2010) | |
Respiration (mitochondria) | Potentially many enzymes, but functional/biochemical consequences are relatively unexplored | Recent studies suggested PTMs for many tricarboxylic acid cycle enzymes, including Lys acetylation and thioredoxin-driven S-S formation; in particular, succinate dehydrogenase and fumarase are inactivated by thioredoxins | Lázaro et al. (2013); Schmidtmann et al. (2014); Daloso et al. (2015) |
PDH | Ser (de)phosphorylation by intrinsic kinase and phosphatase; ammonia and pyruvate control PDH kinase activity; see Figure 1B | Thelen et al. (2000); Tovar-Méndez et al. (2003) | |
C4 cycle (C3 and C4 homologs also involved in glycolysis and/or gluconeogenesis) | Pyruvate orthophosphate dikinase | Phosphorylation by pyruvate orthophosphate dikinase-RP, an S/T bifunctional kinase-phosphatase; in chloroplasts | Chastain et al. (2011); Chen et al. (2014) |
PEPC | Phosphorylation; allosteric regulation by malate and Glc-6-P; in cytosol in mesophyll cells in C4 species (e.g. Panicum maximum); see Figure 1A | Izui et al. (2004); Bailey et al. (2007) | |
PEPC kinase | Ubiquitination resulting in degradation (note also diurnal mRNA levels and linkage to activity level; very low protein level); in cytosol in mesophyll cells in C4 species (e.g. Flaveria spp. and maize) | Agetsuma et al. (2005) | |
PEPC kinase | Phosphorylation in cytosol in bundle sheath cells | Bailey et al. (2007) | |
Starch metabolism (chloroplasts) | ADP-Glc pyrophosphorylase | Redox-regulated disulfide bonds and dynamic oligomerization; thioredoxins; see Figure 1C | Geigenberger et al. (2005); Geigenberger (2011) |
Starch-branching enzyme II | Phosphorylation by Ca2+-dependent protein kinase; P-driven heterooligomerization | Grimaud et al. (2008); Tetlow and Emes (2014) | |
Suc metabolism (cytosol) | SPS (synthesis of Suc) | (De)phosphorylation; SPS kinase and SPS phosphatase; 14-3-3 proteins; cytosol (maize and others) | Huber (2007) |
Suc synthase (breakdown of Suc) | Phosphorylation; Ca2+-dependent protein kinase; correlations to activity, localization, and turnover | Duncan and Huber (2007); Fedosejevs et al. (2014) | |
Photosynthetic electron transport (chloroplast thylakoid membranes) | PSII core and light-harvesting complex proteins | (De)phosphorylation by state-transition kinases (STN7/8) and PP2C phosphatases (PBCP and PPH1/TAP38) | Pesaresi et al. (2011); Tikkanen et al. (2012); Rochaix (2014) |
Nitrogen assimilation | Nitrate reductase | (De)phosphorylation; 14-3-3 proteins | Lillo et al. (2004); Huber (2007) |
6.
Vincent Chochois John P. Vogel Gregory J. Rebetzke Michelle Watt 《Plant physiology》2015,168(3):953-967
Seedling roots enable plant establishment. Their small phenotypes are measured routinely. Adult root systems are relevant to yield and efficiency, but phenotyping is challenging. Root length exceeds the volume of most pots. Field studies measure partial adult root systems through coring or use seedling roots as adult surrogates. Here, we phenotyped 79 diverse lines of the small grass model Brachypodium distachyon to adults in 50-cm-long tubes of soil with irrigation; a subset of 16 lines was droughted. Variation was large (total biomass, ×8; total root length [TRL], ×10; and root mass ratio, ×6), repeatable, and attributable to genetic factors (heritabilities ranged from approximately 50% for root growth to 82% for partitioning phenotypes). Lines were dissected into seed-borne tissues (stem and primary seminal axile roots) and stem-borne tissues (tillers and coleoptile and leaf node axile roots) plus branch roots. All lines developed one seminal root that varied, with branch roots, from 31% to 90% of TRL in the well-watered condition. With drought, 100% of TRL was seminal, regardless of line because nodal roots were almost always inhibited in drying topsoil. Irrigation stimulated nodal roots depending on genotype. Shoot size and tillers correlated positively with roots with irrigation, but partitioning depended on genotype and was plastic with drought. Adult root systems of B. distachyon have genetic variation to exploit to increase cereal yields through genes associated with partitioning among roots and their responsiveness to irrigation. Whole-plant phenotypes could enhance gain for droughted environments because root and shoot traits are coselected.Adult plant root systems are relevant to the size and efficiency of seed yield. They supply water and nutrients for the plant to acquire biomass, which is positively correlated to the harvest index (allocation to seed grain), and the stages of flowering and grain development. Modeling in wheat (Triticum aestivum) suggested that an extra 10 mm of water absorbed by such adult root systems during grain filling resulted in an increase of approximately 500 kg grain ha−1 (Manschadi et al., 2006). This was 25% above the average annual yield of wheat in rain-fed environments of Australia. This number was remarkably close to experimental data obtained in the field in Australia (Kirkegaard et al., 2007). Together, these modeling and field experiments have shown that adult root systems are critical for water absorption and grain yield in cereals, such as wheat, emphasizing the importance of characterizing adult root systems to identify phenotypes for productivity improvements.Most root phenotypes, however, have been described for seedling roots. Seedling roots are essential for plant establishment, and hence, the plant’s potential to set seed. For technical reasons, seedlings are more often screened than adult plants because of the ease of handling smaller plants and the high throughput. Seedling-stage phenotyping may also improve overall reproducibility of results because often, growth media are soil free. Seedling soil-free root phenotyping conditions are well suited to dissecting fine and sensitive mechanisms, such as lateral root initiation (Casimiro et al., 2003; Péret et al., 2009a, 2009b). A number of genes underlying root processes have been identified or characterized using seedlings, notably with the dicotyledonous models Arabidopsis (Arabidopsis thaliana; Mouchel et al., 2004; Fitz Gerald et al., 2006; Yokawa et al., 2013) and Medicago truncatula (Laffont et al., 2010) and the cereals maize (Zea mays; Hochholdinger et al., 2001) and rice (Oryza sativa; Inukai et al., 2005; Kitomi et al., 2008).Extrapolation from seedling to adult root systems presents major questions (Hochholdinger and Zimmermann, 2008; Chochois et al., 2012; Rich and Watt, 2013). Are phenotypes in seedling roots present in adult roots given developmental events associated with aging? Is expression of phenotypes correlated in seedling and adult roots if time compounds effects of growth rates and growth conditions on roots? Watt et al. (2013) showed in wheat seedlings that root traits in the laboratory and field correlated positively but that neither correlated with adult root traits in the field. Factors between seedling and adult roots seemed to be differences in developmental stage and the time that growing roots experience the environment.Seedling and adult root differences may be larger in grasses than dicotyledons. Grass root systems have two developmental components: seed-borne (seminal) roots, of which a number emerge at germination and continue to grow and branch throughout the plant life, and stem-borne (nodal or adventitious) roots, which emerge from around the three-leaf stage and continue to emerge, grow, and branch throughout the plant life. Phenotypes and traits of adult root systems of grasses, which include the major cereal crops wheat, rice, and maize, are difficult to predict in seedling screens and ideally identified from adult root systems first (Gamuyao et al., 2012).Phenotyping of adult roots is possible in the field using trenches (Maeght et al., 2013) or coring (Wasson et al., 2014). A portion of the root system is captured with these methods. Alternatively, entire adult root systems can be contained within pots dug into the ground before sowing. These need to be large; field wheat roots, for example, can reach depths greater than 1.5 m depending on genotype and environment. This method prevents root-root interactions that occur under normal field sowing of a plant canopy and is also a compromise.A solution to the problem of phenotyping adult cereal root systems is a model for monocotyledon grasses: Brachypodium distachyon. B. distachyon is a small-stature grass with a small genome that is fully sequenced (Vogel et al., 2010). It has molecular tools equivalent to those available in Arabidopsis (Draper et al., 2001; Brkljacic et al., 2011; Mur et al., 2011). The root system of B. distachyon reference line Bd21 is more similar to wheat than other model and crop grasses (Watt et al., 2009). It has a seed-borne primary seminal root (PSR) that emerges from the embryo at seed germination and multiple stem-borne coleoptile node axile roots (CNRs) and leaf node axile roots (LNRs), also known as crown roots or adventitious roots, that emerge at about three leaves through to grain development. Branch roots emerge from all root types. There are no known anatomical differences between root types of wheat and B. distachyon (Watt et al., 2009). In a recent study, we report postflowering root growth in B. distachyon line Bd21-3, showing that this model can be used to answer questions relevant to the adult root systems of grasses (Chochois et al., 2012).In this study, we used B. distachyon to identify adult plant phenotypes related to the partitioning among seed-borne and stem-borne shoots and roots for the genetic improvement of well-watered and droughted cereals (Fig. 1; Krassovsky, 1926; Navara et al., 1994), nitrogen, phosphorus (Tennant, 1976; Brady et al., 1995), oxygen (Wiengweera and Greenway, 2004), soil hardness (Acuna et al., 2007), and microorganisms (Sivasithamparam et al., 1978). Of note is the study by Krassovsky (1926), which was the first, to our knowledge, to show differences in function related to water. Krassovsky (1926) showed that seminal roots of wheat absorbed almost 2 times the water as nodal roots per unit dry weight but that nodal roots absorbed a more diluted nutrient solution than seminal roots. Krassovsky (1926) also showed by removing seminal or nodal roots as they emerged that “seminal roots serve the main stem, while nodal roots serve the tillers” (Krassovsky, 1926). Volkmar (1997) showed, more recently, in wheat that nodal and seminal roots may sense and respond to drought differently. In millet (Pennisetum glaucum) and sorghum (Sorghum bicolor), Rostamza et al. (2013) found that millet was able to grow nodal roots in a dryer soil than sorghum, possibly because of shoot and root vigor.Open in a separate windowFigure 1.B. distachyon plant scanned at the fourth leaf stage, with the root and shoot phenotypes studied indicated. Supplemental Table S1.
Open in a separate windowThe third reason for dissecting the different root types in this study was that they seem to have independent genetic regulation through major genes. Genes affecting specifically nodal root growth have been identified in maize (Hetz et al., 1996; Hochholdinger and Feix, 1998) and rice (Inukai et al., 2001, 2005; Liu et al., 2005, 2009; Zhao et al., 2009; Coudert et al., 2010; Gamuyao et al., 2012). Here, we also dissect branch (lateral) development on the seminal or nodal roots. Genes specific to branch roots have been identified in Arabidopsis (Casimiro et al., 2003; Péret et al., 2009a), rice (Hao and Ichii, 1999; Wang et al., 2006; Zheng et al., 2013), and maize (Hochholdinger and Feix, 1998; Hochholdinger et al., 2001; Woll et al., 2005).This study explored the hypothesis that adult root systems of B. distachyon contain genotypic variation that can be exploited through phenotyping and genotyping to increase cereal yields. A selection of 79 wild lines of B. distachyon from various parts of the Middle East (Fig. 2 shows the geographic origins of the lines) was phenotyped. They were selected for maximum genotypic diversity from 187 diploid lines analyzed with 43 simple sequence repeat markers (Vogel et al., 2009). We phenotyped shoots and mature root systems concurrently because B. distachyon is small enough to complete its life cycle in relatively small pots of soil with minimal influence of pot size compared with crops, such as wheat. We further phenotyped a subset of this population under irrigation (well watered) and drought to assess genotype response to water supply. By conducting whole-plant studies, we aimed to identify phenotypes that described partitioning among shoot and root components and within seed-borne and stem-borne roots. Phenotypes that have the potential to be beneficial to shoot and root components may speed up genetic gain in future.Open in a separate windowFigure 2.B. distachyon lines phenotyped in this study and their geographical origin. Capital letters in parentheses indicate the country of origin: Turkey (T), Spain (S), and Iraq (I; Vogel et al., 2009). a, Adi3, Adi7, Adi10, Adi12, Adi13, and Adi15; b, Bd21 and Bd21-3 are the reference lines of this study. Bd21 was the first sequenced line (Vogel et al., 2010) and root system (described in detail in Watt et al., 2009), and Bd21-3 is the most easily transformed line (Vogel and Hill, 2008) and parent of a T-DNA mutant population (Bragg et al., 2012); c, Gaz1, Gaz4, and Gaz7; d, Kah1, Kah2, and Kah3. e, Koz1, Koz3, and Koz5; f, Tek1 and Tek6; g, exact GPS coordinates are unknown for lines Men2 (S), Mur2 (S), Bd2.3 (I), Bd3-1 (I), and Abr1 (T). 相似文献
Phenotype | Abbreviation | Unit | Range of Variation | |
---|---|---|---|---|
All Experiments (79 Lines and 582 Plants) | Experiment 6 (36 Lines) | |||
Whole plant | ||||
TDW | TDW | Milligrams | 88.6–773.8 (×8.7) | 285.6–438 (×1.5) |
Shoot | ||||
SDW | SDW | Milligrams | 56.4–442.5 (×7.8) | 78.2–442.5 (×5.7) |
No. of tillers | TillerN | Count | 2.8–20.3 (×7.4) | 10–20.3 (×2) |
Total root system | ||||
TRL | TRL | Centimeters | 1,050–10,770 (×10.3) | 2,090–5,140 (×2.5) |
RDW | RDW | Milligrams | 28.9–312.17 (×10.8) | 62.2–179.1 (×2.9) |
Rootpc | Rootpc | Percentage (of TDW) | 20.5–60.6 (×3) | 20.5–44.3 (×2.2) |
R/S | R/S | Unitless ratio | 0.26–1.54 (×6) | 0.26–0.80 (×3.1) |
PSRs | ||||
Length (including branch roots) | PSRL | Centimeters | 549.1–4,024.6 (×7.3) | 716–2,984 (×4.2) |
PSRpc | PSRpc | Percentage (of TRL) | 14.9–94.1 (×6.3) | 31.3–72.3 (×2.3) |
No. of axile roots | PSRcount | Count | 1 | 1 |
Length of axile root | PSRsum | Centimeters | 17.45–52 (×3) | 17.45–30.3 (×1.7) |
Branch roots | PSRbranch | Centimeters · (centimeters of axile root)−1 | 19.9–109.3 (×5.5) | 29.3–104.3 (×3.6) |
CNRs | ||||
Length (including branch roots) | CNRL | Centimeters | 0–3,856.7 | 0–2,266.5 |
CNRpc | CNRpc | Percentage (of TRL) | 0–57.1 | 0–49.8 |
No. of axile roots | CNRcount | Count | 0–2 | 0–2 |
Cumulated length of axile roots | CNRsum | Centimeters | 0–113.9 | 0–47.87 |
Branch roots | CNRbranch | Centimeters · (centimeters of axile root)−1 | 0–77.8 | 0–77.8 |
LNRs | ||||
Length (including branch roots) | LNRL | Centimeters | 99.5–5,806.5 (×58.5) | 216.1–2,532.4 (×11.7) |
LNRpc | LNRpc | Percentage (of TRL) | 4.2–72.7 (×17.5) | 6–64.8 (×10.9) |
LNRcount | LNRcount | Count | 2–22.2 (×11.1) | 3.3–15.3 (×4.6) |
LNRsum | LNRsum | Centimeters | 25.9–485.5 | 48–232 (×4.8) |
Branch roots | LNRbranch | Centimeters · (centimeters of axile root)−1 | 2.1–25.4 (×12.1) | 3.2–15.9 (×5) |
7.
Nina I. Lukhovitskaya Graham H. Cowan Ramesh R. Vetukuri Jens Tilsner Lesley Torrance Eugene I. Savenkov 《Plant physiology》2015,167(3):738-752
Recently, it has become evident that nucleolar passage of movement proteins occurs commonly in a number of plant RNA viruses that replicate in the cytoplasm. Systemic movement of Potato mop-top virus (PMTV) involves two viral transport forms represented by a complex of viral RNA and TRIPLE GENE BLOCK1 (TGB1) movement protein and by polar virions that contain the minor coat protein and TGB1 attached to one extremity. The integrity of polar virions ensures the efficient movement of RNA-CP, which encodes the virus coat protein. Here, we report the involvement of nuclear transport receptors belonging to the importin-α family in nucleolar accumulation of the PMTV TGB1 protein and, subsequently, in the systemic movement of the virus. Virus-induced gene silencing of two importin-α paralogs in Nicotiana benthamiana resulted in significant reduction of TGB1 accumulation in the nucleus, decreasing the accumulation of the virus progeny in upper leaves and the loss of systemic movement of RNA-CP. PMTV TGB1 interacted with importin-α in N. benthamiana, which was detected by bimolecular fluorescence complementation in the nucleoplasm and nucleolus. The interaction was mediated by two nucleolar localization signals identified by bioinformatics and mutagenesis in the TGB1 amino-terminal domain. Our results showed that while TGB1 self-interaction is needed for cell-to-cell movement, importin-α-mediated nucleolar targeting of TGB1 is an essential step in establishing the efficient systemic infection of the entire plant. These results enabled the identification of two separate domains in TGB1: an internal domain required for TGB1 self-interaction and cell-to-cell movement and the amino-terminal domain required for importin-α interaction in plants, nucleolar targeting, and long-distance movement.Pomoviruses are causal agents of important diseases affecting potato (Solanum tuberosum), sugar beet (Beta vulgaris), and bean (Phaseolus vulgaris). Potato mop-top virus (PMTV), the type member of the genus Pomovirus, causes an economically important disease of potato called spraing, inducing brown lines and arcs internally and on the surface of tubers. PMTV is transmitted by the root- and tuber-infecting plasmodiophorid Spongospora subterranea (Jones and Harrison, 1969; Arif et al., 1995).The pomovirus genome is divided into three single-stranded RNA (ssRNA) segments of positive polarity. RNA-Rep encodes the putative RNA-dependent RNA polymerase, the replicase of the virus (Savenkov et al., 1999). RNA-CP encodes a coat protein (CP) and another protein called CP-RT or minor CP, which is produced by translational read-through of the CP stop codon (Sandgren et al., 2001). Whereas CP is the major structural protein of the virions, CP-RT is incorporated in one of the termini of the virus particles and a domain within the read-through region of the protein is needed for transmission of the virus by its vector (Reavy et al., 1998). Moreover, CP-RT, but not CP, interacts with the major movement protein TRIPLE GENE BLOCK1 (TGB1; Torrance et al., 2009), which is encoded by RNA-TGB. Besides encoding a triple gene block of movement proteins, TGB1, TGB2, and TGB3 (Zamyatnin et al., 2004), RNA-TGB also encodes a viral suppressor of RNA silencing, the 8K protein (Lukhovitskaya et al., 2013b).To establish a successful infection in the entire plant, viruses must be able to replicate and to move their genomic components between cells, tissues, and organs. Recently, it has become evident that PMTV utilizes a sophisticated mode of cell-to-cell and long-distance movement that involves two virus transport forms, one represented by the viral nucleoprotein complexes (vRNPs) consisting of virus RNA and the TGB1 protein and another represented by the polar virions containing CP-RT and TGB1 proteins attached to one extremity of virus particles (Torrance et al., 2009; for review, see Solovyev and Savenkov, 2014). Proteins implicated in PMTV cell-to-cell movement include TGB1, TGB2, and TGB3 (Zamyatnin et al., 2004; Haupt et al., 2005a). Indirect evidence suggests that CP-RT is required for the efficient systemic movement of intact virions through its interaction with TGB1 (Torrance et al., 2009).Early in infection, the vRNP is transported on the endoplasmic reticulum actomyosin network and targeted to plasmodesmata by TGB2 and TGB3. Later in infection, fluorescently labeled TGB1 is seen in the nucleus and accumulates in the nucleolus. Nucleolar TGB1 association has been shown to be necessary for long-distance movement (Wright et al., 2010).Two structurally distinct subdomains have been identified in the N terminus of TGB1 proteins of hordeiviruses and pomoviruses (Makarov et al., 2009), an N-terminal domain (NTD) comprising approximately 125 amino acids in PMTV (ssRNA in noncooperative and cooperative manners, respectively. The C-terminal half of TGB1 contains a nucleoside triphosphatase/helicase domain that displays cooperative RNA binding. Previously, Wright et al. (2010) reported that TGB1 expressed from a 35S promoter localizes in the cytoplasm and accumulates in the nucleus and nucleolus with occasional labeling of microtubules (MTs). The MT labeling was apparent behind the leading edge of infection when yellow fluorescent protein (YFP)-TGB1 was expressed from an infectious clone. Deletion of 84 amino acids from the N terminus of TGB1 (representing most of the NTD) resulted in the absence of MTs, and nucleolar labeling and fusion of these 84 N-terminal amino acids to GFP resulted in nucleolar enrichment of GFP but no labeling of MTs. Deletion of the 5′ proximal part of the TGB1 open reading frame (ORF), encoding this N-terminal 84 amino acids, in the virus clone abolished systemic but not cell-to-cell movement. However, such deletion had no effect on TGB1 interactions with the CP-RT or self-interaction (Wright et al., 2010).
Open in a separate windowTo better understand the function of TGB1 in PMTV infection, including cell-to-cell movement and targeting the nucleolus, which, in turn, is required for efficient systemic movement, we mapped the TGB1 domains needed for virus cell-to-cell movement, identified nucleolar localization signals (NoLSs) within the NTD, and, using bimolecular fluorescence complementation (BiFC), found that TGB1 was associated with importin-α in the nucleus and nucleolus. TGB1 accumulation in the nucleus, virus accumulation in upper leaves, and virus systemic movement were reduced in Nicotiana benthamiana plants silenced for importin-α. Together, these results suggest that the importin-α-dependent nucleolar association of TGB1 is required for efficient infection by PMTV. 相似文献
Table I.
Structural features of the PMTV TGB1 proteinPositively charged amino acids are set in boldface type and underscored. NoD, Nucleolar localization sequence detector; NS, not shown.TGB1 Sequence | Sequence Location | Predicted Features | Algorithm |
---|---|---|---|
NS | 1 to 125 | Unstructured/disordered domain (NTD) | PDISORDER, IUPred, RONN |
HRVKKD | 11 to 16 | NoLSA | NoD |
FRTNNNKKTQNWKPRS | 37 to 52 | NoLSB | NoD |
NS | 126 to 180 | Ordered domain (internal domain) | PDISORDER, Phyre 2 |
AEFFKSSGLLEKFDFYLSSR | 161 to 180 | α-Helix | PSS Finder, Phyre 2 |
NS | 211 to 436 | Viral superfamily 1 RNA helicases | National Center for Biotechnology Information database |
NS | 211 to 229 | P-loop-containing nucleoside triphosphatase | National Center for Biotechnology Information database |
8.
Laura E. Bartley Matthew L. Peck Sung-Ryul Kim Berit Ebert Chithra Manisseri Dawn M. Chiniquy Robert Sykes Lingfang Gao Carsten Rautengarten Miguel E. Vega-Sánchez Peter I. Benke Patrick E. Canlas Peijian Cao Susan Brewer Fan Lin Whitney L. Smith Xiaohan Zhang Jay D. Keasling Rolf E. Jentoff Steven B. Foster Jizhong Zhou Angela Ziebell Gynheung An Henrik V. Scheller Pamela C. Ronald 《Plant physiology》2013,161(4):1615-1633
9.
Stomata control gaseous fluxes between the internal leaf air spaces and the external atmosphere and, therefore, play a pivotal role in regulating CO2 uptake for photosynthesis as well as water loss through transpiration. Guard cells, which flank the stomata, undergo adjustments in volume, resulting in changes in pore aperture. Stomatal opening is mediated by the complex regulation of ion transport and solute biosynthesis. Ion transport is exceptionally well understood, whereas our knowledge of guard cell metabolism remains limited, despite several decades of research. In this review, we evaluate the current literature on metabolism in guard cells, particularly the roles of starch, sucrose, and malate. We explore the possible origins of sucrose, including guard cell photosynthesis, and discuss new evidence that points to multiple processes and plasticity in guard cell metabolism that enable these cells to function effectively to maintain optimal stomatal aperture. We also discuss the new tools, techniques, and approaches available for further exploring and potentially manipulating guard cell metabolism to improve plant water use and productivity.Stomata are microscopic, adjustable pores on the leaf surface. The evolution of stomata more than 400 million years ago (Edwards et al., 1986, 1992, 1998) helped facilitate the adaptation of plants to a terrestrial environment, where water is typically a limiting resource. Each stoma is composed of two kidney- or dumbbell-shaped guard cells, whose volume changes to adjust pore aperture, allowing plants to simultaneously regulate CO2 uptake and water loss. This facilitation of gas exchange by stomatal opening is one of the most essential processes in plant photosynthesis and transpiration, affecting plant water use efficiency and agricultural crop yields (Lawson and Blatt, 2014).Plant physiologists have a long history of investigating the behavior of these fascinating structures, reaching back more than a century to the pioneering work of Sir Francis Darwin (Darwin, 1916) and the American botanist Francis Ernest Lloyd (Lloyd, 1908). Major contributions to stomatal research arose from inventing and improving equipment and methods for quantitatively measuring the effects of environmental factors on stomatal pore aperture. After Darwin’s work, it became clear that the stomatal aperture actively responds to changes in the environment and regulates leaf transpiration rates (Meidner, 1987). Over the past century, much has been learned about their structure, development, and physiology.Despite the anatomical simplicity of the stomatal valve, the surrounding guard cells are highly specialized. Guard cells are morphologically distinct from general epidermal cells and possess complex signal transduction networks, elevated membrane ion transport capacity, and modified metabolic pathways. These features allow rapid modulations in guard cell turgor in response to endogenous and environmental signals, promoting the opening and closure of the stomatal pore in time scales of seconds to hours (Assmann and Wang, 2001). A variety of osmotically active solutes contribute to the buildup of stomatal turgor. Potassium (K+) and chloride (Cl−) act as the main inorganic ions, and malate2− and sucrose (Suc) function as the main organic solutes. Whereas K+ and Cl− are taken up from the apoplast, Suc and malate2− can be imported or synthesized internally using carbon skeletons deriving from starch degradation and/or CO2 fixation in the guard cell chloroplast (Roelfsema and Hedrich, 2005; Vavasseur and Raghavendra, 2005; Lawson, 2009; Kollist et al., 2014). The accumulation of these osmotica lowers the water potential, promoting the inflow of water, the swelling of guard cells, and the opening of the stomatal pore. Most of the ions taken up, or synthesized by guard cells, are sequestered into the vacuole (Barbier-Brygoo et al., 2011). As a result, the guard cell vacuoles undergo dynamic changes in volume and structure, which are crucial for achieving the full amplitude of stomatal movements (Gao et al., 2005; Tanaka et al., 2007; Andrés et al., 2014). During stomatal closure, guard cells reduce their volume through the release of ions into the cell wall and the consequent efflux of water.The transport of osmolytes across the plasma and tonoplast guard cell membranes is energized by H+-ATPase activity, which generates a proton motive force by translocating H+ ions against their concentration gradient (Blatt, 1987a, 1987b; Thiel et al., 1992; Roelfsema and Hedrich, 2005; Gaxiola et al., 2007). After the pioneering work of Fischer demonstrated the importance of K+ uptake in stomatal opening (Fischer, 1968; Fischer and Hsiao, 1968), K+ transport became of central interest and has long been considered the essence of stomatal movement regulation. The development of the voltage clamp technique, along with the relative easy acquisition of knockout mutants and transgenics in the model plant Arabidopsis (Arabidopsis thaliana), helped to uncover the precise mechanism and function of K+ fluxes in guard cells. It is well established that changes in membrane potential in response to several stimuli (e.g. light/darkness, CO2, and abscisic acid [ABA]) alter the direction of K+ transport (Thiel et al., 1992; Blatt, 2000; Roelfsema et al., 2001, 2002, 2004). During stomatal opening, the activation of the proton pump generates a sufficiently negative electric potential to cause the uptake of K+ through the inward-rectifying K+ channels (K+in; Fig. 1). During stomatal closure, K+ outflow from outward-rectifying K+ channels (K+out) results from membrane depolarization (Fig. 2; Blatt, 1988; Schroeder, 1988; Anderson et al., 1992; Sentenac et al., 1992). Besides being gated by opposing changes in voltage, the activation of (K+out) channels is dependent on the extracellular K+ concentration, while that of K+in is not (Blatt, 1988, 1992; Roelfsema and Prins, 1997; Dreyer and Blatt, 2009). There is also strong evidence for H+-coupled K+ symport in guard cells, which could account for up to 50% of total K+ uptake during stomatal opening (Blatt and Clint, 1989; Clint and Blatt, 1989; Hills et al., 2012). At least for K+in, the loss of a single-channel gene in Arabidopsis has little or no impact on stomatal movement (Szyroki et al., 2001), showing the redundancy among the different K+in isoforms and of K+ transport in general.Open in a separate windowFigure 1.Integration of guard cell carbohydrate metabolism with membrane ion transport during stomatal opening. Sugars in guard cells can be imported from the apoplast, derive from starch breakdown, or be synthesized in the Calvin cycle. These sugars then can be stored as osmotically active solutes in the vacuole or metabolized in the cytosol to yield energy, reducing equivalents, and phosphoenolpyruvate (PEP). PEP can be further metabolized to pyruvate in the mitochondrial tricarboxylic acid (CAC) cycle or used as carbon skeletons for the biosynthesis of malate via PEP carboxylase (PEPC) and NAD-dependent malate dehydrogenase (NAD-MDH). Malate (which also can be imported from the apoplast) and the inorganic ions K+ and Cl− accumulate in the vacuole, lowering the guard cell osmotic potential, thereby promoting stomatal opening. ABCB14, ATP-binding cassette transporter B14; AcetylCoA, acetyl-CoA; ALMT, aluminum-activated malate transporter; ATP-PFK, ATP-dependent phosphofructokinase; AttDT, dicarboxylate transporter; cINV, cytosolic invertase; cwINV, cell wall invertase; Fru6P, Fru-6-P; Fru1,6P2, fructose 1,6-bisphosphate; Gl6P, Glc-6-P; G3P, glyceraldehyde 3-phosphate; iPGAM, phosphoglycerate mutase isoforms; NRGA1, negative regulator of guard cell ABA signaling1; OAA, oxaloacetate; 2-PGA, 2-phosphoglycerate; 3-PGA, 3-phosphoglycerate; PPi-PFK, PPi-dependent Fru-6-P phosphotransferase; STP, monosaccharide/H+ cotransporter; SUC, Suc/H+ cotransporter; SuSy, Suc synthase; TPT, triose phosphate/phosphate translocator. Compartments are not to scale. The dotted line indicates multiple metabolic steps.Open in a separate windowFigure 2.Proposed pathways of osmolyte dissipation during stomatal closure. While the removal of Cl− and K+ is well described in the literature, the fate of Suc and malate during stomatal closure is unclear. Suc can be cleaved by cytosolic invertase (cINV), and the resulting hexoses can be imported into the chloroplast in the form of Glc-6-P (Glc6P). Glc6P is used subsequently for starch biosynthesis. Malate can be removed from the cell via decarboxylation to pyruvate by malic enzyme (ME) and the subsequent complete oxidation in the mitochondrial tricarboxylic acid (CAC) cycle. Alternatively, malate can be converted to PEP via NAD+-dependent malate dehydrogenase (NAD-MDH) and PEP carboxykinase (PEPCK). Gluconeogenic conversion of PEP to Glc6P establishes a possible link between malate removal and starch synthesis. Compartments are not to scale. PEP, Phosphoenolpyruvate; OAA; oxaloacetate; STP, monosaccharide/H+ cotransporter; SUC, Suc/H+ cotransporter; SuSy, Suc synthase; cINV, cytosolic invertase; NRGA1, negative regulator of guard cell ABA signaling1; ALMT, aluminum-activated malate transporter; GPT, Glc-6-P/Pi translocator; cwINV, cell wall invertase; HK, hexokinase; QUAC1, quickly activating anion channel1.Despite the undisputed importance of K+ uptake in stomatal opening, the accumulation of K+ ions alone cannot account for the increase in osmotic pressure necessary to explain stomatal aperture. Studies from the 1980s by MacRobbie and Fischer demonstrated that Vicia faba guard cells take up approximately 2 pmol of K+ during stomatal opening. Assuming that K+ uptake is balanced by the accumulation of similar amounts of counter ions (Cl− and/or malate2−), the expected increase in stomatal turgor to approximately 3 MPa is less than the 4.5 MPa expected for fully open stomata (Fischer, 1972; MacRobbie and Lettau, 1980a, 1980b; Chen et al., 2012). The realization that other solutes must accumulate in addition to K+ salts was one of the major paradigm shifts in stomatal physiology research in the last decades, equal to the discovery of ion channels. Suc was put forward as the most likely candidate for the additional osmoticum to support stomatal opening (MacRobbie, 1987; Tallman and Zeiger, 1988; Talbott and Zeiger, 1993, 1998). Nonetheless, this research area subsequently failed to attract notice commensurate with its importance.In the last few years, the metabolism of starch, sugars and, organic acids in guard cells has seen a rebirth, making this the perfect time to review the developments in this field. In this review, we focus on photosynthetic carbon assimilation and respiratory metabolism in guard cells and provide a historical overview of the subject that highlights the most up-to-date and novel discoveries in guard cell research. We describe the various metabolic pathways separately, but as metabolism is an integrated network, we also discuss their reciprocal and beneficial interactions. Finally, we highlight their connection with the metabolism in the subjacent mesophyll cells and how they integrate with guard cell signal transduction networks and membrane ion transport to regulate stomatal movements. The enzymes and transporters discussed in this review are listed in Arabidopsis Genome Initiative Code Gene Protein Function Malate transport AT1G28010 ABCB14 ATP-binding cassette transporter B14 Import of apoplastic malate AT5G47560 tDT Dicarboxylate transporter Transport of carboxylates into the vacuole AT3G18440 ALMT9 Aluminum-activated malate transporter9 Transport of Cl−/malate2− into the vacuole AT2G17470 ALMT6 Aluminum-activated malate transporter6 Transport of malate2− into the vacuole AT4G17970 ALMT12/QUAC1 Aluminum-activated malate transporter12 Export of cytosolic Cl−/malate2− to the apoplast Malate metabolism – PEPC Phosphoenolpyruvate carboxylase β-Carboxylation of PEP to OAA – NAD-MDH NAD+-dependent malate dehydrogenase Reduction of OAA to malate – ME Malic enzyme Oxidative decarboxylation of malate to pyruvate AT4G37870 PEPCK1 PEP carboxykinase1 Conversion of OAA to PEP – PPDK Pyruvate, orthophosphate dikinase Conversion of pyruvate to PEP Other carboxylates – TPT Triose phosphate/phosphate translocator Export of triose phosphate from the chloroplast to the cytosol AT4G05590 NRGA1 Negative regulator of guard cell ABA signaling1 Putative mitochondrial pyruvate carrier – SDH2 Succinate dehydrogenase2 Oxidation of succinate to fumarate AT2G47510 FUM1 Fumarase1 Hydration of fumarate to malate – iPGAM Phosphoglycerate mutase Interconversion of 3-PGA to 2-PGA – PPi-PFK PPi-dependent Fru-6-P phosphotransferase Phosphorylation of Fru-6-P to Fru-1,6-bisphosphate – ATP-PFK ATP-dependent phosphofructokinase Phosphorylation of Fru-6-P to Fru-1,6-bisphosphate Calvin cycle – Rubisco Rubisco Carboxylation of ribulose 1,5-bisphosphate AT3G55800 SBPase Sedoheptulose-bisphosphatase Dephosphorylation of sedoheptulose-1,7-bisphosphate to sedoheptulose-7-phosphate Sugar metabolism AT4G29130 HK1 Hexokinase1 Phosphorylation of Glc to Glc-6-P AT4G02280 SuSy Suc synthase3 Interconversion of Suc to Fru and UDP-Glc – cINV Cytosolic invertase Hydrolysis of Suc to Fru and Glc – cwINV Cell wall invertase Hydrolysis of Suc to Fru and Glc Sugar transport AT1G11260 STP1 Monosaccharide/H+ cotransporter1 Import of apoplastic hexose sugars AT3G19930 STP4 Monosaccharide/H+ cotransporter4 Import of apoplastic hexose sugars AT1G71880 SUC1 Suc/H+ cotransporter1 Import of apoplastic Suc AT2G02860 SUC3 Suc/H+ cotransporter3 Import of apoplastic Suc Starch degradation AT3G23920 BAM1 β-Amylase1 Hydrolysis of α-1,4 external glucoside linkages in starch AT1G69830 AMY3 α-Amylase3 Hydrolysis of α-1,4 internal glucoside linkages in starch Starch synthesis – GPT Glc-6-P/Pi translocator Uptake of cytosolic Glc-6-P into the chloroplast AT4G24620 PGI Phosphoglucose isomerase Conversion of Fru-6-P to Glc-6-P AT5G51820 PGM1 Phosphoglucomutase1 Conversion of Glc-6-P to Glc-1-P AT5G48300 APS1 ADPGlc pyrophosphorylase small subunit Conversion of Glc-1-P to ADPGlc, catalytic subunit – APL ADPGlc pyrophosphorylase large subunit Conversion of Glc-1-P to ADPGlc, regulatory subunit Various AT3G45780 PHOT1 Phototropin1 Blue light photoreceptor AT5G58140 PHOT2 Phototropin2 Blue light photoreceptor AT4G14480 BLUS1 Blue light signaling1 Protein kinase, regulator of blue light-induced stomatal opening – PP1 Protein phosphatase1 Regulator of blue light-induced stomatal opening AT3G01500 CA1 Carbonic anhydrase1 Interconversion of CO2 and water into H2CO3 AT1G70410 CA4 Carbonic anhydrase4 Interconversion of CO2 and water into H2CO3 AT1G62400 HT1 High leaf temperature1 Protein kinase, regulator of CO2-induced stomatal closure