Alfalfa leaf senescence induced by drought stress: photosynthesis, hydrogen peroxide metabolism, lipid peroxidation and ethylene evolution

Exchange rates of CO₂ and H₂O and metabolism of hydrogen peroxide have been measured in leaves of alfalfa ev. Aragón) under drought stress. The inhibitory effect of drought upon photosynthesis depended on the severity of the stress treatment. Leaf water potential (Ψ_leaf) down to,-2.8 MPa reduced CO₂ availability due to stomatal closure and inhibited the rate of photosynthesis. Leaf water potential lower than,-2.8 MPa directly affected CO₂ fixation, although CO₂ was not limiting. Transpiration was more affected by stornatal closure than photosynthesis, which led to am apparent improvement in WUE (water use efficiency). Alfalfa leaves with Ψ_leaf lower than,-2.0 MPa had an increased quantum requirement, probably due to the severe stress effect on photoenergetic reactions.
Ethylene evolution from alfalfa leaves increased when they were subjected to Ψ_leaf of,- 1.6 MPa. Under more severe stress, the leaves showed low or almost no ethylene production. In parallel with the increase in ethyiene production, alfalfa leaves exhibited an increased membrane lipid peroxidation index (maloridialdehyde content) and an increased peroxide content. Superoxide disinutase activity (SOD; EC 1.15.1.1) was not affected by drought stress. Catalase (EC 1.11.1.6) was inhibited at slight stress, but significantly increased at a Ψ_leaf of -2.0 MPa. Peroxidase (EC 1.11.1.7) was progressively inhibited as drought stress developed. The possible implication of reactive O₂ intermediates in drought stress-induced senescence of alfalfa leaves is discussed in the light of the pattern of enzymatic scavenging systems.     

The effect of water stress on photosynthesis and related parameters in Pinus halepensis

Net photosynthesis, transpiration, dark respiration rates and stomatal and mesophyll resistances were studied in young potted seedlings of Pinus halepensis Mill. under gradually decreasing soil and leaf water potentials. Stomatal resistance under non-limiting xylem water potentials was 6–7 times higher than mesophyll resistance. Stomata started to close at threshold xylem water potentials of −0.8 MPa, whereas mesophyll resistance started to increase at about −1.4 MPa. Decreasing xylem water potentials increased the CO₂ compensation point and decreased the water use efficiency (expressed by the photosynthesis to transpiration ratio) and dark respiration rate. It is concluded that at least part of the drought resistance characteristics of P. halepensis are associated with a sensitive stomatal mechanism which enables an efficient control of water loss.     

Use of the response of photosynthesis to oxygen to estimate mesophyll conductance to carbon dioxide in water-stressed soybean leaves

Methods of estimating the mesophyll conductance (g_m) to the movement of CO₂ from the substomatal airspace to the site of fixation are expensive or rely upon numerous assumptions. It is proposed that, for C₃ species, measurement of the response of photosynthesis to [O₂] at limiting [CO₂], combined with a standard biochemical model of photosynthesis, can provide an estimate of g_m. This method was used to determine whether g_m changed with [CO₂] and with water stress in soybean leaves. The value of g_m estimated using the O₂ response method agreed with values obtained using other methods. The g_m was unchanged over the tested range of substomatal [CO₂]. Water stress, which decreased stomatal conductance (g_s) by about 80%, did not affect g_m, while the model parameter V_Cmax was reduced by about 25%. Leaves with g_s reduced by about 90% had g_m values reduced by about 50%, while V_Cmax was reduced by about 64%. It is concluded that g_m in C₃ species can be conveniently estimated using the response of photosynthesis to [O₂] at limiting [CO₂], and that g_m in soybean was much less sensitive to water stress than g_s, and was somewhat less sensitive to water stress than V_Cmax.     

Stomatal and non-stomatal limitations of photosynthesis in trees of a tropical seasonally flooded forest

Trees in the flooded forest of the Mapire River in Venezuela suffer a decrease in photosynthetic rate (A) when flood begins, which is reverted at maximum flood. Changes in A are accompanied by similar changes in stomatal conductance (g_s), and the possibility of changes in photosynthetic capacity is not ruled out. In order to understand how relative stomatal and non-stomatal limitations of photosynthesis are affected by flooding, we studied the seasonal changes in A and its response to intercellular CO₂ concentration in trees of Campsiandra laurifolia , Symmeria paniculata , Acosmium nitens and Eschweilera tenuifolia . Flooding caused in trees of C.   laurifolia and S.   paniculata a reduction in A, g_s, carboxylation efficiency and total soluble protein (TSP), whereas gas exchange in A.   nitens and E.   tenuifolia was more sensitive to drought. Under flooding, relative stomatal limitation (L_s) was on average half the highest, and relative non-stomatal limitation (L_ns) increased from the dry season to flooding. Under full flood, A, g_s and TSP regained high values. A was positively correlated to light-saturated electron transport rate, suggesting that part of the decrease in A under flooding was due to impairment of photosynthetic capacity. Under flooding, not only stomatal closure but also increased L_ns causes a reduction in photosynthesis of all four species, and a process of acclimation as flooding progresses allows gas exchange and related variables to regain high values.     

Stomatal behaviour, photosynthesis and transpiration under rising CO2

Definitions of the variables used and the units are given in Table 1

The literature reports enormous variation between species in the extent of stomatal responses to rising CO₂. This paper attempts to provide a framework within which some of this diversity can be explained. We describe the role of stomata in the short-term response of leaf gas exchange to increases in ambient CO₂ concentration by developing the recently proposed stomatal model of Jarvis & Davies (1998 ). In this model stomatal conductance is correlated with the functioning of the photosynthetic system so that the effects of increases in CO₂ on stomata are experienced through changes in the rate of photosynthesis in a simple and mechanistically transparent way. This model also allows us to consider the effects of evaporative demand and soil moisture availability on stomatal responses to photosynthesis and therefore provides a means of considering these additional sources of variation. We emphasize that the relationship between the rate of photosynthesis and the internal CO₂ concentration and also drought will have important effects on the relative gains to be achieved under rising CO₂.  

  Table 1 . Abbreviations     

6.

Air pollution in the past recorded in width and stable carbon isotope composition of annual growth rings of Douglas-fir   总被引：4，自引：2，他引：2  

B. MARTIN  E. K. SUTHERLAND 《Plant, cell & environment》1990,13(8):839-844

Abstract. Tree-ring indices (TRIs) of annual growth rings in stems of Douglas-fir ( Pseudotsuga menziesii ) growing near a copper smelter showed reduced growth during two multi-year time periods in the past. These periods coincided with World Wars I and II, which are known to represent periods of particularly high SO₂ emissions from the smelter. Reduced growth was correlated with less negative stable carbon isotope composition (δ¹³C) in cellulose purified from wood formed in such years. Based on current models for ¹³C/¹²C in plants, these results indicate that exposure to air pollution resulted in reduced concentration of CO₂ in the intercellular air spaces of the needles. This is consistent with the hypothesis that stomatal closure resulted in impaired photosynthesis and reduced growth during past episodes of high air pollution. The pollution-related change in δ¹³C was superimposed on a change with time in δ¹³C, independent of growth, by - 1.4 per mil from 1902 to 1984.     

7.

Photosynthesis, photochemistry and antioxidative defence in response to two drought severities and with re-watering in Allocasuarina luehmannii     

S. Posch  & L. T. Bennett 《Plant biology (Stuttgart, Germany)》2009,11(S1):83-93

Gas exchange, chlorophyll fluorescence and water potentials, together with ascorbate and glutathione concentrations, were studied during moderate and severe drought stress and in response to re-watering in Allocasuarina luehmannii seedlings. Moderate drought stress (MS) decreased stomatal conductance (g_s) and net CO₂ assimilation rates (A) to ∼40% and ∼60% of control values, respectively, and caused decreases in internal CO₂ concentration (C_i) and maximum light use efficiency of light-acclimated photosystem II (PSII) centres (Fv'/Fm'). Severe drought stress (SS) decreased g_s and A to ∼5% and ∼15% of the control values, respectively, and caused increases in C_i and PSII excitation pressure (1 − qP), as well as decreases in water potentials, effective quantum yield of PSII (ΦPSII), maximum efficiency of PSII (Fv/Fm) and Fv'/Fm'. Ascorbate and glutathione concentrations remained unaffected by drought treatments, but ascorbate became more oxidised under severe stress. MS seedlings recovered within 1 day (C_i, Fv'/Fm') to 1 week (A, g_s) of re-watering. In comparison, SS seedlings had longer-lasting after-stress effects, with recovery of many variables (g_s, water potentials, Fv/Fm, ΦPSII, Fv'/Fm') taking between 1 and 3 weeks from re-watering. We found no indication that interaction with antioxidants played a significant role in recovery. In conclusion, A. luehmannii seedlings appear to function normally under moderate drought, but do not seem to have particular metabolic tolerance mechanisms to endure severe drought, which may have implications for its persistence under climate change at the drier margins of its distribution.     

8.

Low carbon dioxide concentrations can reverse stomatal closure during water stress     

James A. Bunce 《Physiologia plantarum》2007,130(4):552-559

Leaf water potentials below threshold values result in reduced stomatal conductance (g_s). Stomatal closure at low leaf water potentials may serve to protect against cavitation of xylem. Possible control of g_s by leaf water potential or hydraulic conductance was tested by drying the rooting medium in four herbaceous annual species until g_s was reduced and then lowering the [CO₂] to determine whether g_s and transpiration rate could be increased and leaf water potential decreased and whether hydraulic conductance was reduced at the resulting lower leaf water potential. In all species, low [CO₂] could reverse the stomatal closure because of drying despite further reductions in leaf water potential, and the resulting lower leaf water potentials did not result in reductions in hydraulic conductance. The relative sensitivity of g_s to internal [CO₂] in the leaves of dry plants of each species averaged three to four times higher than in leaves of wet plants. Two species in which g_s was reputed to be insensitive to [CO₂] were examined to determine whether high leaf to air water vapor pressure differences (D) resulted in increased stomatal sensitivity to [CO₂]. In both species, stomatal sensitivity to [CO₂] was indeed negligible at low D, but increased with D, and low [CO₂] partly or fully reversed closure caused by high D. In no case did low leaf water potential or low hydraulic conductance during drying of the air or the rooting medium prevent low [CO₂] from increasing g_s and transpiration rate.     

9.

Exchange of oxygen and its role in energy dissipation during drought stress in tomato plants   总被引：10，自引：0，他引：10  

Silke Haupt-Herting  Heinrich P. F_ock 《Physiologia plantarum》2000,110(4):489-495

To elucidate how excess light energy is dissipated during water deficit, net photosynthesis (P_N), stomatal conductance (g_s), intercellular CO₂ concentration (c_i) and Chl a fluorescence were investigated in control and drought-stressed tomato plants ( Lycopersicon esculentum ). Gross O₂ evolution (E_o) and gross O₂ uptake (U_o) were determined by a mass spectrometric ¹⁶O/¹⁸O₂ isotope technique. Under drought stress P_N, g_s, c_i and U_o decline. While photochemical fluorescence quenching decreases under water deficit, non-photochemical quenching rises. The maximal efficiency of PSII measured in the dark is not affected by drought; however, in the light, E_o decreases under water deficit. The ratio P_N/E_o falls under stress while the ratio U_o/E_o increases. We conclude that tomato plants follow a double strategy to avoid photodamage under drought stress conditions: (1) a substantial portion of light energy is emitted as heat and PSII activity is downregulated. This results in a decrease in E_o as well as P_N and U_o. Despite reduced charge separation at PSII, the decline of CO₂ assimilation because of lowered stomatal conductance and metabolic changes results in the need of degrading excessive photosynthetic electrons. (2) Oxygen is used as an alternative electron acceptor in photorespiration or Mehler reaction and U_o rises relative to E_o.     

10.

Responses of individual stomata in Ipomoea pes-caprae to various CO2 concentrations     

Kamakura M  Furukawa A 《Physiologia plantarum》2008,132(3):255-261

The responses of individual stomata to CO₂ concentrations ranging from 0 to 900 μmol mol⁻¹ air were analysed in Ipomoea pes-caprae L. Sweet (Convolvulaceae). The stomata were directly observed using a measurement system that permitted continuous observation of stomatal movement under controlled light and CO₂ conditions. A CO₂ concentration of 350 μmol mol⁻¹ or higher induced stomatal closure, whereas concentrations below 350 μmol mol⁻¹ did not. The time lag before stomatal closure decreased with increasing CO₂ concentration, as did the steady-state aperture of the stomata after a change in CO₂ concentration. However, the rate of stomatal closure increased with increasing CO₂ concentration. Therefore, not only the stomatal closure rate but also the time from the CO₂ concentration change to the beginning of stomatal closure changed with increasing CO₂ concentration. These results suggest that atmospheric CO₂ may be the stimulus for the closure of guard cells. No significant differences were observed between adaxial and abaxial stomata in terms of their responses to CO₂. However, heterogeneous responses were detected between neighbouring stomata on each leaf surface.     

11.

Genetic variation in photosynthetic capacity, carbon isotope discrimination and mesophyll conductance in provenances of Castanea sativa adapted to different environments   总被引：10，自引：0，他引：10  

M. LAUTERI  A. SCARTAZZA  M. C. GUIDO  & E. BRUGNOLI 《Functional ecology》1997,11(6):675-683

1. Provenances of Castanea sativa from populations adapted to different climatic areas of Turkey were grown in a field trial in Italy. Carbon isotope discrimination (Δ) in leaf dry matter and in leaf soluble sugar, were measured, along with photosynthesis, stomatal conductance and mesophyll conductance, to study the variability of primary productivity and its ecological significance in European Chestnut.
2. Genetic variations were found in RuBP carboxylase, chlorophyll, leaf soluble protein and leaf thickness.
3. Carbon isotope discrimination (Δ) in leaf dry matter was greater in drought-adapted than in wet-adapted provenances. A similar variation of Δ was observed in leaf soluble carbohydrates either under watered or drought conditions. Possible environmental effects of variables such as vapour pressure difference, on the relationship between transpiration efficiency and carbon isotope discrimination are discussed, on the basis of short-term and long-term results.
4. Generally low values of Δ encountered among provenances were explained not only by low values of intercellular CO₂ partial pressure but also by consistently low values of mesophyll conductance leading to reduced chloroplastic CO₂ partial pressure. A decrease in mesophyll conductance was induced by water shortage. Co-ordination was found between stomatal and mesophyll conductance, with the drought-adapted provenances showing much higher mesophyll conductance than the wet-adapted provenances. Variations in mesophyll conductance were related to differences in leaf protein content.
5. Possible ecophysiological adaptive mechanisms are discussed taking into account stomatal sensitivity, modulation of photosynthetic capacity and water-use efficiency under drought conditions.     

12.

Stomatal responses to CO₂ during a diel Crassulacean acid metabolism cycle in Kalanchoe daigremontiana and Kalanchoe pinnata     

SUSANNE VON CAEMMERER  & HOWARD GRIFFITHS 《Plant, cell & environment》2009,32(5):567-576

To investigate the diurnal variation of stomatal sensitivity to CO₂, stomatal response to a 30 min pulse of low CO₂ was measured four times during a 24 h time-course in two Crassulacean acid metabolism (CAM) species Kalanchoe daigremontiana and Kalanchoe pinnata , which vary in the degree of succulence, and hence, expression and commitment to CAM. In both species, stomata opened in response to a reduction in p CO₂ in the dark and in the latter half of the light period, and thus in CAM species, chloroplast photosynthesis is not required for the stomatal response to low p CO₂. Stomata did not respond to a decreased p CO₂ in K. daigremontiana in the light when stomata were closed, even when the supply of internal CO₂ was experimentally reduced. We conclude that stomatal closure during phase III is not solely mediated by high internal p CO₂, and suggest that in CAM species the diurnal variability in the responsiveness of stomata to p CO₂ could be explained by hypothesizing the existence of a single CO₂ sensor which interacts with other signalling pathways. When not perturbed by low p CO₂, CO₂ assimilation rate and stomatal conductance were correlated both in the light and in the dark in both species.     

13.

Investigation of the limitations to photosynthesis induced by leaf water deficit in field-grown sunflower (Helianthus annuus L.)   总被引：1，自引：1，他引：0  

R. R. WISE  J. R. FREDERICK  D. M. ALM  †  D. M. KRAMER  J. D. HESKETH  A. R. CROFTS  D. R. ORT 《Plant, cell & environment》1990,13(9):923-931

Abstract. The diurnal cycling of leaf water potential (Ψ_leaf) in field-grown sunflower ( Helianthus annuus ) was used to investigate the cause of water deficitinduced limitation of net photosynthesis. Daily midafternoon decreases in Ψ_leaf of up to 1.5 MPa and in net photosynthesis of up to 50% were typical for irrigated sunflower during seed filling. These midafternoon values were lowered an additional 0.6 to 0.8 MPa by prolonged drought treatment. There was a nearly linear relationship between the decline in net photosynthesis and reductions in leaf conductance over the course of the day. Thus, it was unexpected to find that the low, midafternoon rates of photosynthesis were associated with the highest intercellular CO₂ concentrations. These and other observations suggest that the daily decline in photosynthesis represents a 'down regulation' of the biochemical demand for CO₂ that is coordinated with the diurnally developing need to conserve water, thus establishing a balanced limitation of photosynthesis involving both stomatal and non-stomatal factors. There were no indications that either short term (i.e. diurnal declines in Ψ_leaf) or long term (i.e. drought treatment) water deficits caused any damage or malfunctioning of photosynthesis. Rather, both the daily declines in photosynthesis and the nearly 25% decrease in leaf area induced by prolonged drought appeared to be well-controlled adaptive responses by field-grown sunflower plants to limited water availability.     

14.

Modelling environmental controls on ecosystem photosynthesis and the carbon isotope composition of ecosystem-respired CO2 in a coastal Douglas-fir forest     

Cai T  Flanagan LB  Jassal RS  Black TA 《Plant, cell & environment》2008,31(4):435-453

We developed and applied an ecosystem-scale model that calculated leaf CO₂ assimilation, stomatal conductance, chloroplast CO₂ concentration and the carbon isotope composition of carbohydrate formed during photosynthesis separately for sunlit and shaded leaves within multiple canopy layers. The ecosystem photosynthesis model was validated by comparison to leaf-level gas exchange measurements and estimates of ecosystem-scale photosynthesis from eddy covariance measurements made in a coastal Douglas-fir forest on Vancouver Island. A good agreement was also observed between modelled and measured δ ¹³C values of ecosystem-respired CO₂ ( δ _R). The modelled δ _R values showed strong responses to variation in photosynthetic photon flux density (PPFD), air temperature, vapour pressure deficit (VPD) and available soil moisture in a manner consistent with leaf-level studies of photosynthetic ¹³C discrimination. Sensitivity tests were conducted to evaluate the effect of (1) changes in the lag between the time of CO₂ fixation and the conversion of organic matter back to CO₂; (2) shifts in the proportion of autotrophic and heterotrophic respiration; (3) isotope fractionation during respiration; and (4) environmentally induced changes in mesophyll conductance, on modelled δ _R values. Our results indicated that δ _R is a good proxy for canopy-level C _c/ C _a and ¹³C discrimination during photosynthetic gas exchange, and therefore has several applications in ecosystem physiology.     

15.

Diurnal variations of photosynthesis and dew absorption by leaves in two evergreen shrubs growing in Mediterranean field conditions   总被引：15，自引：0，他引：15  

SERGI MUNNÉ-BOSCH  SALVADOR NOGUÉS  & LEONOR ALEGRE 《The New phytologist》1999,144(1):109-119

The effects of summer drought, dew deposition on leaves and autumn rainfall on plant water relations and diurnal variations of photosynthesis were measured in two evergreen shrubs, rosemary ( Rosmarinus officinalis ) and lavender ( Lavandula stoechas ), grown in Mediterranean field conditions. Withholding water for 40 d caused a similar decrease in predawn shoot water potential (ψ_pd) from c. −0.4 to c. −1.3 MPa in both species, but a 50% decrease in the relative leaf water content in L. stoechas compared with 22% in R. officinalis . A similar decrease in CO₂ assimilation rates by c. 75% was observed in water-stressed plants of both species, although L. stoechas showed smaller photosynthesis: stomatal conductance ratio than R. officinalis (35 vs 45 μmol CO₂:mol H₂O). The relative quantum efficiency of photosystem II photochemistry also decreased by c. 45% at midday in water- stressed plants of both species. Nevertheless, neither L. stoechas nor R. officinalis suffered drought-induced damage to photosystem II, as indicated by the maintenance of the ratio F _v: F _m throughout the experiment, associated with an increase in the carotenoid content per unit of chlorophyll by c. 62% and c. 30%, respectively, in water-stressed plants. Only L. stoechas absorbed dew by leaves. In this species the occurrence of 6 d of dew over a 15-d period improved relative leaf water content by c. 72% and shoot water potential by c. 0.5 MPa throughout the day in water-stressed plants, although the photosynthetic capacity was not recovered until the occurrence of autumn rainfall. The ability of leaves to absorb dew allowed L. stoechas to restore plant water status, which is especially relevant in plants exposed to prolonged drought.     

16.

Distinct light responses of the adaxial and abaxial stomata in intact leaves of Helianthus annuus L     

Wang Y  Noguchi K  Terashima I 《Plant, cell & environment》2008,31(9):1307-1316

Using a laboratory-constructed system that can measure the gas exchange rates of two leaf surfaces separately, the light responses of the adaxial and abaxial stomata in intact leaves of sunflower ( Helianthus annuus L.) were investigated, keeping the intercellular CO₂ concentration ( C _i) at 300  µ L L⁻¹. When evenly illuminating both sides of the leaf, the stomatal conductance ( g _s) of the abaxial surface was higher than that of the adaxial surface at any light intensity. When each surface of the leaf was illuminated separately, both the adaxial and abaxial stomata were more sensitive to the light transmitted through the leaf (self-transmitted light) than to direct illumination. Relationships between the whole leaf photosynthetic rate ( A _n) and the g _s for each side highlighted a strong dependence of stomatal opening on mesophyll photosynthesis. Light transmitted through another leaf was more effective than the direct white light for the abaxial stomata, but not for the adaxial stomata. Moreover, green monochromatic light induced an opening of the abaxial stomata, but not of the adaxial stomata. As the proportion of blue light in the transmitted light is less than that in the white light, there may be some uncharacterized light responses, which are responsible for the opening of the abaxial stomata by the transmitted, green light.     

17.

Stomatal sensing of the environment   总被引：1，自引：0，他引：1  

C. M. WILLMER 《Biological journal of the Linnean Society. Linnean Society of London》1988,34(3):205-217

The effects of environmental factors on stomatal behaviour are reviewed and the questions of whether photosynthesis and transpiration eontrol stomata or whether stomata themselves control the rates of these processes is addressed. Light affects stomata directly and indirectly. Light can act directly as an energy source resulting in ATP formation within guard cells via photophosphorylation, or as a stimulus as in the case of the blue light effects which cause guard cell H⁺ extrusion. Light also acts indirectly on stomata by affecting photosynthesis which influences the intercellular leaf CO₂ concentration ( C _i). Carbon dioxide concentrations in contact with the plasma membrane of the guard cell or within the guard cell acts directly on cell processes responsible for stomatal movements. The mechanism by which CO₂ exerts its effect is not fully understood but, at least in part, it is concerned with changing the properties of guard cell plasma membranes which influence ion transport processes. The C _i may remain fairly constant for much of the day for many species which is the result of parallel responses of stomata and photosynthesis to light. Leaf water potential also influences stomatal behaviour. Since leaf water potential is a resultant of water uptake and storage by the plant and transpirational water loss, any factor which affects these processes, such as soil water availability, temperature, atmospheric humidity and air movement, may indirectly affect stomata. Some of these factors, such as temperature and possibly humidity, may affect stomata directly. These direct and indirect effects of environmental factors interact to give a net opening response upon which is superimposed a direct effect of stomatal circadian rhythmic activity.     

18.

The role of the mesophyll in stomatal responses to light and CO2   总被引：1，自引：0，他引：1  

Mott KA  Sibbernsen ED  Shope JC 《Plant, cell & environment》2008,31(9):1299-1306

Stomatal responses to light and CO₂ were investigated using isolated epidermes of Tradescantia pallida , Vicia faba and Pisum sativum . Stomata in leaves of T. pallida and P. sativum responded to light and CO₂, but those from V. faba did not. Stomata in isolated epidermes of all three species could be opened on KCl solutions, but they showed no response to light or CO₂. However, when isolated epidermes of T. pallida and P. sativum were placed on an exposed mesophyll from a leaf of the same species or a different species, they regained responsiveness to light and CO₂. Stomatal responses in these epidermes were similar to those in leaves in that they responded rapidly and reversibly to changes in light and CO₂. Epidermes from V. faba did not respond to light or CO₂ when placed on mesophyll from any of the three species. Experiments with single optic fibres suggest that stomata were being regulated via signals from the mesophyll produced in response to light and CO₂ rather than being sensitized to light and CO₂ by the mesophyll. The data suggest that most of the stomatal response to CO₂ and light occurs in response to a signal generated by the mesophyll.     

19.

Direct and indirect effects of light on stomata II. In Commelina communis L.   总被引：2，自引：2，他引：0  

J. I. L.  MORISON  P. G. JARVIS 《Plant, cell & environment》1983,6(2):103-109

Abstract. Two experiments are described which test the normal correlations that arise between stomatal conductance, net CO₂ assimilation rate, and intercellular CO₂ concentration (C_i), using whole shoots of Commelina communis L. In the first, conductance increased with decreasing C_i, at four different quantum flux densities, such that there was no unique relationship between conductance and quantum flux density or C_i, In the second, conductance increased hyperbolically with increasing quantum flux density while C_i was held constant at 466, 302, and 46 μmiolmol⁻¹, and the response differed at each C_i. In neither experiment was conductance consistently related to net CO₂ assimilation rate in the mesophyll. In both experiments high C_i suppressed the response of conductance to light, while there was a large response of conductance to light at low C_i, indicating an interaction between the effects of light and CO₂ on stomata. The results show that the parallel responses of assimilation and conductance to light result in constant intercellular CO₂ concentrations, and not that stomata maintain a 'constant C_i'.     

20.

Photorespiration in C4 grasses remains slow under drought conditions     

Carmo-Silva AE  Powers SJ  Keys AJ  Arrabaça MC  Parry MA 《Plant, cell & environment》2008,31(7):925-940

The CO₂-concentrating mechanism present in C₄ plants decreases the oxygenase activity of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) and, consequently, photorespiratory rates in air. Under drought conditions, the intercellular CO₂ concentration may decrease and cause photorespiration to increase. The C₄ grasses Paspalum dilatatum Poiret, Cynodon dactylon (L.) Pers. and Zoysia japonica Steudel were grown in soil and drought was imposed by ceasing to provide water. Net CO₂ assimilation ( A ) and stomatal conductance to water vapour decreased with leaf dehydration. Decreased carbon and increased oxygen isotope composition were also observed under drought. The response of A to CO₂ suggested that the compensation point was zero in all species irrespective of the extent of drought stress. A slight decrease of A as O₂ concentration increased above 10% provided evidence for slow photorespiratory gas exchanges. Analysis of amino acids contained in the leaves, particularly the decrease of glycine after 30 s in darkness, supported the presence of slow photorespiration rates, but these were slightly faster in Cynodon dactylon than in Paspalum dilatatum and Zoysia japonica . Although the contents of glycine and serine increased with dehydration and mechanistic modelling of C₄ photosynthesis suggested slightly increased photorespiration rates in proportion to photosynthesis, the results provide evidence that photorespiration remained slow under drought conditions.     

Air pollution in the past recorded in width and stable carbon isotope composition of annual growth rings of Douglas-fir

Abstract. Tree-ring indices (TRIs) of annual growth rings in stems of Douglas-fir ( Pseudotsuga menziesii ) growing near a copper smelter showed reduced growth during two multi-year time periods in the past. These periods coincided with World Wars I and II, which are known to represent periods of particularly high SO₂ emissions from the smelter. Reduced growth was correlated with less negative stable carbon isotope composition (δ¹³C) in cellulose purified from wood formed in such years. Based on current models for ¹³C/¹²C in plants, these results indicate that exposure to air pollution resulted in reduced concentration of CO₂ in the intercellular air spaces of the needles. This is consistent with the hypothesis that stomatal closure resulted in impaired photosynthesis and reduced growth during past episodes of high air pollution. The pollution-related change in δ¹³C was superimposed on a change with time in δ¹³C, independent of growth, by - 1.4 per mil from 1902 to 1984.     

Photosynthesis, photochemistry and antioxidative defence in response to two drought severities and with re-watering in Allocasuarina luehmannii

Gas exchange, chlorophyll fluorescence and water potentials, together with ascorbate and glutathione concentrations, were studied during moderate and severe drought stress and in response to re-watering in Allocasuarina luehmannii seedlings. Moderate drought stress (MS) decreased stomatal conductance (g_s) and net CO₂ assimilation rates (A) to ∼40% and ∼60% of control values, respectively, and caused decreases in internal CO₂ concentration (C_i) and maximum light use efficiency of light-acclimated photosystem II (PSII) centres (Fv'/Fm'). Severe drought stress (SS) decreased g_s and A to ∼5% and ∼15% of the control values, respectively, and caused increases in C_i and PSII excitation pressure (1 − qP), as well as decreases in water potentials, effective quantum yield of PSII (ΦPSII), maximum efficiency of PSII (Fv/Fm) and Fv'/Fm'. Ascorbate and glutathione concentrations remained unaffected by drought treatments, but ascorbate became more oxidised under severe stress. MS seedlings recovered within 1 day (C_i, Fv'/Fm') to 1 week (A, g_s) of re-watering. In comparison, SS seedlings had longer-lasting after-stress effects, with recovery of many variables (g_s, water potentials, Fv/Fm, ΦPSII, Fv'/Fm') taking between 1 and 3 weeks from re-watering. We found no indication that interaction with antioxidants played a significant role in recovery. In conclusion, A. luehmannii seedlings appear to function normally under moderate drought, but do not seem to have particular metabolic tolerance mechanisms to endure severe drought, which may have implications for its persistence under climate change at the drier margins of its distribution.     

Low carbon dioxide concentrations can reverse stomatal closure during water stress

Leaf water potentials below threshold values result in reduced stomatal conductance (g_s). Stomatal closure at low leaf water potentials may serve to protect against cavitation of xylem. Possible control of g_s by leaf water potential or hydraulic conductance was tested by drying the rooting medium in four herbaceous annual species until g_s was reduced and then lowering the [CO₂] to determine whether g_s and transpiration rate could be increased and leaf water potential decreased and whether hydraulic conductance was reduced at the resulting lower leaf water potential. In all species, low [CO₂] could reverse the stomatal closure because of drying despite further reductions in leaf water potential, and the resulting lower leaf water potentials did not result in reductions in hydraulic conductance. The relative sensitivity of g_s to internal [CO₂] in the leaves of dry plants of each species averaged three to four times higher than in leaves of wet plants. Two species in which g_s was reputed to be insensitive to [CO₂] were examined to determine whether high leaf to air water vapor pressure differences (D) resulted in increased stomatal sensitivity to [CO₂]. In both species, stomatal sensitivity to [CO₂] was indeed negligible at low D, but increased with D, and low [CO₂] partly or fully reversed closure caused by high D. In no case did low leaf water potential or low hydraulic conductance during drying of the air or the rooting medium prevent low [CO₂] from increasing g_s and transpiration rate.     

Exchange of oxygen and its role in energy dissipation during drought stress in tomato plants

To elucidate how excess light energy is dissipated during water deficit, net photosynthesis (P_N), stomatal conductance (g_s), intercellular CO₂ concentration (c_i) and Chl a fluorescence were investigated in control and drought-stressed tomato plants ( Lycopersicon esculentum ). Gross O₂ evolution (E_o) and gross O₂ uptake (U_o) were determined by a mass spectrometric ¹⁶O/¹⁸O₂ isotope technique. Under drought stress P_N, g_s, c_i and U_o decline. While photochemical fluorescence quenching decreases under water deficit, non-photochemical quenching rises. The maximal efficiency of PSII measured in the dark is not affected by drought; however, in the light, E_o decreases under water deficit. The ratio P_N/E_o falls under stress while the ratio U_o/E_o increases. We conclude that tomato plants follow a double strategy to avoid photodamage under drought stress conditions: (1) a substantial portion of light energy is emitted as heat and PSII activity is downregulated. This results in a decrease in E_o as well as P_N and U_o. Despite reduced charge separation at PSII, the decline of CO₂ assimilation because of lowered stomatal conductance and metabolic changes results in the need of degrading excessive photosynthetic electrons. (2) Oxygen is used as an alternative electron acceptor in photorespiration or Mehler reaction and U_o rises relative to E_o.     

Responses of individual stomata in Ipomoea pes-caprae to various CO2 concentrations

The responses of individual stomata to CO₂ concentrations ranging from 0 to 900 μmol mol⁻¹ air were analysed in Ipomoea pes-caprae L. Sweet (Convolvulaceae). The stomata were directly observed using a measurement system that permitted continuous observation of stomatal movement under controlled light and CO₂ conditions. A CO₂ concentration of 350 μmol mol⁻¹ or higher induced stomatal closure, whereas concentrations below 350 μmol mol⁻¹ did not. The time lag before stomatal closure decreased with increasing CO₂ concentration, as did the steady-state aperture of the stomata after a change in CO₂ concentration. However, the rate of stomatal closure increased with increasing CO₂ concentration. Therefore, not only the stomatal closure rate but also the time from the CO₂ concentration change to the beginning of stomatal closure changed with increasing CO₂ concentration. These results suggest that atmospheric CO₂ may be the stimulus for the closure of guard cells. No significant differences were observed between adaxial and abaxial stomata in terms of their responses to CO₂. However, heterogeneous responses were detected between neighbouring stomata on each leaf surface.     

Genetic variation in photosynthetic capacity, carbon isotope discrimination and mesophyll conductance in provenances of Castanea sativa adapted to different environments

1. Provenances of Castanea sativa from populations adapted to different climatic areas of Turkey were grown in a field trial in Italy. Carbon isotope discrimination (Δ) in leaf dry matter and in leaf soluble sugar, were measured, along with photosynthesis, stomatal conductance and mesophyll conductance, to study the variability of primary productivity and its ecological significance in European Chestnut.
2. Genetic variations were found in RuBP carboxylase, chlorophyll, leaf soluble protein and leaf thickness.
3. Carbon isotope discrimination (Δ) in leaf dry matter was greater in drought-adapted than in wet-adapted provenances. A similar variation of Δ was observed in leaf soluble carbohydrates either under watered or drought conditions. Possible environmental effects of variables such as vapour pressure difference, on the relationship between transpiration efficiency and carbon isotope discrimination are discussed, on the basis of short-term and long-term results.
4. Generally low values of Δ encountered among provenances were explained not only by low values of intercellular CO₂ partial pressure but also by consistently low values of mesophyll conductance leading to reduced chloroplastic CO₂ partial pressure. A decrease in mesophyll conductance was induced by water shortage. Co-ordination was found between stomatal and mesophyll conductance, with the drought-adapted provenances showing much higher mesophyll conductance than the wet-adapted provenances. Variations in mesophyll conductance were related to differences in leaf protein content.
5. Possible ecophysiological adaptive mechanisms are discussed taking into account stomatal sensitivity, modulation of photosynthetic capacity and water-use efficiency under drought conditions.     

Stomatal responses to CO2 during a diel Crassulacean acid metabolism cycle in Kalanchoe daigremontiana and Kalanchoe pinnata

To investigate the diurnal variation of stomatal sensitivity to CO₂, stomatal response to a 30 min pulse of low CO₂ was measured four times during a 24 h time-course in two Crassulacean acid metabolism (CAM) species Kalanchoe daigremontiana and Kalanchoe pinnata , which vary in the degree of succulence, and hence, expression and commitment to CAM. In both species, stomata opened in response to a reduction in p CO₂ in the dark and in the latter half of the light period, and thus in CAM species, chloroplast photosynthesis is not required for the stomatal response to low p CO₂. Stomata did not respond to a decreased p CO₂ in K. daigremontiana in the light when stomata were closed, even when the supply of internal CO₂ was experimentally reduced. We conclude that stomatal closure during phase III is not solely mediated by high internal p CO₂, and suggest that in CAM species the diurnal variability in the responsiveness of stomata to p CO₂ could be explained by hypothesizing the existence of a single CO₂ sensor which interacts with other signalling pathways. When not perturbed by low p CO₂, CO₂ assimilation rate and stomatal conductance were correlated both in the light and in the dark in both species.     

Investigation of the limitations to photosynthesis induced by leaf water deficit in field-grown sunflower (Helianthus annuus L.)

Abstract. The diurnal cycling of leaf water potential (Ψ_leaf) in field-grown sunflower ( Helianthus annuus ) was used to investigate the cause of water deficitinduced limitation of net photosynthesis. Daily midafternoon decreases in Ψ_leaf of up to 1.5 MPa and in net photosynthesis of up to 50% were typical for irrigated sunflower during seed filling. These midafternoon values were lowered an additional 0.6 to 0.8 MPa by prolonged drought treatment. There was a nearly linear relationship between the decline in net photosynthesis and reductions in leaf conductance over the course of the day. Thus, it was unexpected to find that the low, midafternoon rates of photosynthesis were associated with the highest intercellular CO₂ concentrations. These and other observations suggest that the daily decline in photosynthesis represents a 'down regulation' of the biochemical demand for CO₂ that is coordinated with the diurnally developing need to conserve water, thus establishing a balanced limitation of photosynthesis involving both stomatal and non-stomatal factors. There were no indications that either short term (i.e. diurnal declines in Ψ_leaf) or long term (i.e. drought treatment) water deficits caused any damage or malfunctioning of photosynthesis. Rather, both the daily declines in photosynthesis and the nearly 25% decrease in leaf area induced by prolonged drought appeared to be well-controlled adaptive responses by field-grown sunflower plants to limited water availability.     

Modelling environmental controls on ecosystem photosynthesis and the carbon isotope composition of ecosystem-respired CO2 in a coastal Douglas-fir forest

We developed and applied an ecosystem-scale model that calculated leaf CO₂ assimilation, stomatal conductance, chloroplast CO₂ concentration and the carbon isotope composition of carbohydrate formed during photosynthesis separately for sunlit and shaded leaves within multiple canopy layers. The ecosystem photosynthesis model was validated by comparison to leaf-level gas exchange measurements and estimates of ecosystem-scale photosynthesis from eddy covariance measurements made in a coastal Douglas-fir forest on Vancouver Island. A good agreement was also observed between modelled and measured δ ¹³C values of ecosystem-respired CO₂ ( δ _R). The modelled δ _R values showed strong responses to variation in photosynthetic photon flux density (PPFD), air temperature, vapour pressure deficit (VPD) and available soil moisture in a manner consistent with leaf-level studies of photosynthetic ¹³C discrimination. Sensitivity tests were conducted to evaluate the effect of (1) changes in the lag between the time of CO₂ fixation and the conversion of organic matter back to CO₂; (2) shifts in the proportion of autotrophic and heterotrophic respiration; (3) isotope fractionation during respiration; and (4) environmentally induced changes in mesophyll conductance, on modelled δ _R values. Our results indicated that δ _R is a good proxy for canopy-level C _c/ C _a and ¹³C discrimination during photosynthetic gas exchange, and therefore has several applications in ecosystem physiology.     

Diurnal variations of photosynthesis and dew absorption by leaves in two evergreen shrubs growing in Mediterranean field conditions

The effects of summer drought, dew deposition on leaves and autumn rainfall on plant water relations and diurnal variations of photosynthesis were measured in two evergreen shrubs, rosemary ( Rosmarinus officinalis ) and lavender ( Lavandula stoechas ), grown in Mediterranean field conditions. Withholding water for 40 d caused a similar decrease in predawn shoot water potential (ψ_pd) from c. −0.4 to c. −1.3 MPa in both species, but a 50% decrease in the relative leaf water content in L. stoechas compared with 22% in R. officinalis . A similar decrease in CO₂ assimilation rates by c. 75% was observed in water-stressed plants of both species, although L. stoechas showed smaller photosynthesis: stomatal conductance ratio than R. officinalis (35 vs 45 μmol CO₂:mol H₂O). The relative quantum efficiency of photosystem II photochemistry also decreased by c. 45% at midday in water- stressed plants of both species. Nevertheless, neither L. stoechas nor R. officinalis suffered drought-induced damage to photosystem II, as indicated by the maintenance of the ratio F _v: F _m throughout the experiment, associated with an increase in the carotenoid content per unit of chlorophyll by c. 62% and c. 30%, respectively, in water-stressed plants. Only L. stoechas absorbed dew by leaves. In this species the occurrence of 6 d of dew over a 15-d period improved relative leaf water content by c. 72% and shoot water potential by c. 0.5 MPa throughout the day in water-stressed plants, although the photosynthetic capacity was not recovered until the occurrence of autumn rainfall. The ability of leaves to absorb dew allowed L. stoechas to restore plant water status, which is especially relevant in plants exposed to prolonged drought.     

Distinct light responses of the adaxial and abaxial stomata in intact leaves of Helianthus annuus L

Using a laboratory-constructed system that can measure the gas exchange rates of two leaf surfaces separately, the light responses of the adaxial and abaxial stomata in intact leaves of sunflower ( Helianthus annuus L.) were investigated, keeping the intercellular CO₂ concentration ( C _i) at 300  µ L L⁻¹. When evenly illuminating both sides of the leaf, the stomatal conductance ( g _s) of the abaxial surface was higher than that of the adaxial surface at any light intensity. When each surface of the leaf was illuminated separately, both the adaxial and abaxial stomata were more sensitive to the light transmitted through the leaf (self-transmitted light) than to direct illumination. Relationships between the whole leaf photosynthetic rate ( A _n) and the g _s for each side highlighted a strong dependence of stomatal opening on mesophyll photosynthesis. Light transmitted through another leaf was more effective than the direct white light for the abaxial stomata, but not for the adaxial stomata. Moreover, green monochromatic light induced an opening of the abaxial stomata, but not of the adaxial stomata. As the proportion of blue light in the transmitted light is less than that in the white light, there may be some uncharacterized light responses, which are responsible for the opening of the abaxial stomata by the transmitted, green light.     

Stomatal sensing of the environment

The effects of environmental factors on stomatal behaviour are reviewed and the questions of whether photosynthesis and transpiration eontrol stomata or whether stomata themselves control the rates of these processes is addressed. Light affects stomata directly and indirectly. Light can act directly as an energy source resulting in ATP formation within guard cells via photophosphorylation, or as a stimulus as in the case of the blue light effects which cause guard cell H⁺ extrusion. Light also acts indirectly on stomata by affecting photosynthesis which influences the intercellular leaf CO₂ concentration ( C _i). Carbon dioxide concentrations in contact with the plasma membrane of the guard cell or within the guard cell acts directly on cell processes responsible for stomatal movements. The mechanism by which CO₂ exerts its effect is not fully understood but, at least in part, it is concerned with changing the properties of guard cell plasma membranes which influence ion transport processes. The C _i may remain fairly constant for much of the day for many species which is the result of parallel responses of stomata and photosynthesis to light. Leaf water potential also influences stomatal behaviour. Since leaf water potential is a resultant of water uptake and storage by the plant and transpirational water loss, any factor which affects these processes, such as soil water availability, temperature, atmospheric humidity and air movement, may indirectly affect stomata. Some of these factors, such as temperature and possibly humidity, may affect stomata directly. These direct and indirect effects of environmental factors interact to give a net opening response upon which is superimposed a direct effect of stomatal circadian rhythmic activity.     

The role of the mesophyll in stomatal responses to light and CO2

Stomatal responses to light and CO₂ were investigated using isolated epidermes of Tradescantia pallida , Vicia faba and Pisum sativum . Stomata in leaves of T. pallida and P. sativum responded to light and CO₂, but those from V. faba did not. Stomata in isolated epidermes of all three species could be opened on KCl solutions, but they showed no response to light or CO₂. However, when isolated epidermes of T. pallida and P. sativum were placed on an exposed mesophyll from a leaf of the same species or a different species, they regained responsiveness to light and CO₂. Stomatal responses in these epidermes were similar to those in leaves in that they responded rapidly and reversibly to changes in light and CO₂. Epidermes from V. faba did not respond to light or CO₂ when placed on mesophyll from any of the three species. Experiments with single optic fibres suggest that stomata were being regulated via signals from the mesophyll produced in response to light and CO₂ rather than being sensitized to light and CO₂ by the mesophyll. The data suggest that most of the stomatal response to CO₂ and light occurs in response to a signal generated by the mesophyll.     

Direct and indirect effects of light on stomata II. In Commelina communis L.

Abstract. Two experiments are described which test the normal correlations that arise between stomatal conductance, net CO₂ assimilation rate, and intercellular CO₂ concentration (C_i), using whole shoots of Commelina communis L. In the first, conductance increased with decreasing C_i, at four different quantum flux densities, such that there was no unique relationship between conductance and quantum flux density or C_i, In the second, conductance increased hyperbolically with increasing quantum flux density while C_i was held constant at 466, 302, and 46 μmiolmol⁻¹, and the response differed at each C_i. In neither experiment was conductance consistently related to net CO₂ assimilation rate in the mesophyll. In both experiments high C_i suppressed the response of conductance to light, while there was a large response of conductance to light at low C_i, indicating an interaction between the effects of light and CO₂ on stomata. The results show that the parallel responses of assimilation and conductance to light result in constant intercellular CO₂ concentrations, and not that stomata maintain a 'constant C_i'.     

Photorespiration in C4 grasses remains slow under drought conditions

The CO₂-concentrating mechanism present in C₄ plants decreases the oxygenase activity of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) and, consequently, photorespiratory rates in air. Under drought conditions, the intercellular CO₂ concentration may decrease and cause photorespiration to increase. The C₄ grasses Paspalum dilatatum Poiret, Cynodon dactylon (L.) Pers. and Zoysia japonica Steudel were grown in soil and drought was imposed by ceasing to provide water. Net CO₂ assimilation ( A ) and stomatal conductance to water vapour decreased with leaf dehydration. Decreased carbon and increased oxygen isotope composition were also observed under drought. The response of A to CO₂ suggested that the compensation point was zero in all species irrespective of the extent of drought stress. A slight decrease of A as O₂ concentration increased above 10% provided evidence for slow photorespiratory gas exchanges. Analysis of amino acids contained in the leaves, particularly the decrease of glycine after 30 s in darkness, supported the presence of slow photorespiration rates, but these were slightly faster in Cynodon dactylon than in Paspalum dilatatum and Zoysia japonica . Although the contents of glycine and serine increased with dehydration and mechanistic modelling of C₄ photosynthesis suggested slightly increased photorespiration rates in proportion to photosynthesis, the results provide evidence that photorespiration remained slow under drought conditions.