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1.
Levillain J Thongo M'Bou A Deleporte P Saint-André L Jourdan C 《Annals of botany》2011,108(1):221-230
Background and Aims
Despite their importance for plant production, estimations of below-ground biomass and its distribution in the soil are still difficult and time consuming, and no single reliable methodology is available for different root types. To identify the best method for root biomass estimations, four different methods, with labour requirements, were tested at the same location.Methods
The four methods, applied in a 6-year-old Eucalyptus plantation in Congo, were based on different soil sampling volumes: auger (8 cm in diameter), monolith (25 × 25 cm quadrate), half Voronoi trench (1·5 m3) and a full Voronoi trench (3 m3), chosen as the reference method.Key Results
With the reference method (0–1m deep), fine-root biomass (FRB, diameter <2 mm) was estimated at 1·8 t ha−1, medium-root biomass (MRB diameter 2–10 mm) at 2·0 t ha−1, coarse-root biomass (CRB, diameter >10 mm) at 5·6 t ha−1 and stump biomass at 6·8 t ha−1. Total below-ground biomass was estimated at 16·2 t ha−1 (root : shoot ratio equal to 0·23) for this 800 tree ha−1 eucalypt plantation density. The density of FRB was very high (0·56 t ha−1) in the top soil horizon (0–3 cm layer) and decreased greatly (0·3 t ha−1) with depth (50–100 cm). Without labour requirement considerations, no significant differences were found between the four methods for FRB and MRB; however, CRB was better estimated by the half and full Voronoi trenches. When labour requirements were considered, the most effective method was auger coring for FRB, whereas the half and full Voronoi trenches were the most appropriate methods for MRB and CRB, respectively.Conclusions
As CRB combined with stumps amounted to 78 % of total below-ground biomass, a full Voronoi trench is strongly recommended when estimating total standing root biomass. Conversely, for FRB estimation, auger coring is recommended with a design pattern accounting for the spatial variability of fine-root distribution. 相似文献2.
Background and Aims
When root-zone O2 deficiency occurs together with salinity, regulation of shoot ion concentrations is compromised even more than under salinity alone. Tolerance was evaluated amongst 34 accessions of Hordeum marinum, a wild species in the Triticeae, to combined salinity and root-zone O2 deficiency. Interest in H. marinum arises from the potential to use it as a donor for abiotic stress tolerance into wheat.Methods
Two batches of 17 H. marinum accessions, from (1) the Nordic Gene Bank and (2) the wheat belt of Western Australia, were exposed to 0·2 or 200 mol m−3 NaCl in aerated or stagnant nutrient solution for 28–29 d. Wheat (Triticum aestivum) was included as a sensitive check species. Growth, root porosity, root radial O2 loss (ROL) and leaf ion (Na+, K+, Cl−) concentrations were determined.Key Results
Owing to space constraints, this report is focused mainly on the accessions from the Nordic Gene Bank. The 17 accessions varied in tolerance; relative growth rate was reduced by 2–38 % in stagnant solution, by 8–42 % in saline solution (aerated) and by 39–71 % in stagnant plus saline treatment. When in stagnant solution, porosity of adventitious roots was 24–33 %; salinity decreased the root porosity in some accessions, but had no effect in others. Roots grown in stagnant solution formed a barrier to ROL, but variation existed amongst accessions in apparent barrier ‘strength’. Leaf Na+ concentration was 142–692 µmol g−1 d. wt for plants in saline solution (aerated), and only increased to 247–748 µmol g−1 d. wt in the stagnant plus saline treatment. Leaf Cl− also showed only small effects of stagnant plus saline treatment, compared with saline alone. In comparison with H. marinum, wheat was more adversely affected by each stress alone, and particularly when combined; growth reductions were greater, adventitious root porosity was 21 %, it lacked a barrier to ROL, leaf K+ declined to lower levels, and leaf Na+ and Cl− concentrations were 3·1–9-fold and 2·8–6-fold higher, respectively, in wheat.Conclusions
Stagnant treatment plus salinity reduced growth more than salinity alone, or stagnant alone, but some accessions of H. marinum were still relatively tolerant of these combined stresses, maintaining Na+ and Cl− ‘exclusion’ even in an O2-deficient, saline rooting medium.Key words: Aerenchyma, combined salinity and waterlogging, leaf Cl−, leaf K+, leaf Na+, radial O2 loss, salt tolerance, salinity–waterlogging interaction, sea barleygrass, waterlogging tolerance, wheat, wild Triticeae 相似文献3.
Background and Aims
Formation of cluster roots is one of the most specific root adaptations to nutrient deficiency. In white lupin (Lupinus albus), cluster roots can be induced by phosphorus (P) or iron (Fe) deficiency. The aim of the present work was to investigate the potential shared signalling pathway in P- and Fe-deficiency-induced cluster root formation.Methods
Measurements were made of the internal concentration of nutrients, levels of nitric oxide (NO), citrate exudation and expression of some specific genes under four P × Fe combinations, namely (1) 50 µm P and 10 µm Fe (+P + Fe); (2) 0 P and 10 µm Fe (–P + Fe); (3) 50 µm P and 0 Fe (+P–Fe); and (4) 0 P and 0 Fe (–P–Fe), and these were examined in relation to the formation of cluster roots.Key Results
The deficiency of P, Fe or both increased the cluster root number and cluster zones. It also enhanced NO accumulation in pericycle cells and rootlet primordia at various stages of cluster root development. The formation of cluster roots and rootlet primordia, together with the expression of LaSCR1 and LaSCR2 which is crucial in cluster root formation, were induced by the exogenous NO donor S-nitrosoglutathione (GSNO) under the +P + Fe condition, but were inhibited by the NO-specific endogenous scavenger 2-(4-carboxyphenyl)-4, 4, 5, 5-tetramethylimidazoline-1-oxyl- 3-oxide (cPTIO) under –P + Fe, +P–Fe and –P–Fe conditions. However, cluster roots induced by an exogenous supply of the NO donor did not secrete citrate, unlike those formed under –P or –Fe conditions.Conclusions
NO plays an important role in the shared signalling pathway of the P- and Fe-deficiency-induced formation of cluster roots in white lupin. 相似文献4.
Background and Aims
Haberlea rhodopensis is a perennial, herbaceous, saxicolous, poikilohydric flowering plant that is able to survive desiccation to air-dried state under irradiance below 30 µmol m−2 s−1. However, desiccation at irradiance of 350 µmol m−2 s−1 induced irreversible changes in the photosynthetic apparatus, and mature leaves did not recover after rehydration. The aim here was to establish the causes and mechanisms of irreversible damage of the photosynthetic apparatus due to dehydration at high irradiance, and to elucidate the mechanisms determining recovery.Methods
Changes in chloroplast structure, CO2 assimilation, chlorophyll fluorescence parameters, fluorescence imaging and the polypeptide patterns during desiccation of Haberlea under medium (100 µmol m−2 s−1; ML) irradiance were compared with those under low (30 µmol m−2 s−1; LL) irradiance.Key Results
Well-watered plants (control) at 100 µmol m−2 s−1 were not damaged. Plants desiccated at LL or ML had similar rates of water loss. Dehydration at ML decreased the quantum efficiency of photosystem II photochemistry, and particularly the CO2 assimilation rate, more rapidly than at LL. Dehydration induced accumulation of stress proteins in leaves under both LL and ML. Photosynthetic activity and polypeptide composition were completely restored in LL plants after 1 week of rehydration, but changes persisted under ML conditions. Electron microscopy of structural changes in the chloroplast showed that the thylakoid lumen is filled with an electron-dense substance (dense luminal substance, DLS), while the thylakoid membranes are lightly stained. Upon dehydration and rehydration the DLS thinned and disappeared, the time course largely depending on the illumination: whereas DLS persisted during desiccation and started to disappear during late recovery under LL, it disappeared from the onset of dehydration and later was completely lost under ML.Conclusions
Accumulation of DLS (possibly phenolics) in the thylakoid lumen is demonstrated and is proposed as a mechanism protecting the thylakoid membranes of H. rhodopensis during desiccation and recovery under LL. Disappearance of DLS during desiccation in ML could leave the thylakoid membranes without protection, allowing oxidative damage during dehydration and the initial rehydration, thus preventing recovery of photosynthesis.Key words: Haberlea rhodopensis, resurrection plant, electron microscopy, blue–green fluorescence, chlorophyll fluorescence 相似文献5.
Background and Aims
Soil salinity is often heterogeneous, yet the physiology of halophytes has typically been studied with uniform salinity treatments. An evaluation was made of the growth, net photosynthesis, water use, water relations and tissue ions in the halophytic shrub Atriplex nummularia in response to non-uniform NaCl concentrations in a split-root system.Methods
Atriplex nummularia was grown in a split-root system for 21 d, with either the same or two different NaCl concentrations (ranging from 10 to 670 mm), in aerated nutrient solution bathing each root half.Key Results
Non-uniform salinity, with high NaCl in one root half (up to 670 mm) and 10 mm in the other half, had no effect on shoot ethanol-insoluble dry mass, net photosynthesis or shoot pre-dawn water potential. In contrast, a modest effect occurred for leaf osmotic potential (up to 30 % more solutes compared with uniform 10 mm NaCl treatment). With non-uniform NaCl concentrations (10/670 mm), 90 % of water was absorbed from the low salinity side, and the reduction in water use from the high salinity side caused whole-plant water use to decrease by about 30 %; there was no compensatory water uptake from the low salinity side. Leaf Na+ and Cl− concentrations were 1·9- to 2·3-fold higher in the uniform 670 mm treatment than in the 10/670 mm treatment, whereas leaf K+ concentrations were 1·2- to 2·0-fold higher in the non-uniform treatment.Conclusions
Atriplex nummularia with one root half in 10 mm NaCl maintained net photosynthesis, shoot growth and shoot water potential even when the other root half was exposed to 670 mm NaCl, a concentration that inhibits growth by 65 % when uniform in the root zone. Given the likelihood of non-uniform salinity in many field situations, this situation would presumably benefit halophyte growth and physiology in saline environments.Key words: Split-root system, salinity heterogeneity, root zone heterogeneity, water potential, water use, stomatal conductance, saltbush, leaf ions, photosynthesis, NaCl 相似文献6.
Linking carbon supply to root cell-wall chemistry and mechanics at high altitudes in Abies georgei 总被引:3,自引:0,他引:3
Background and Aims
The mobile carbon supply to different compartments of a tree is affected by climate, but its impact on cell-wall chemistry and mechanics remains unknown. To understand better the variability in root growth and biomechanics in mountain forests subjected to substrate mass movement, we investigated root chemical and mechanical properties of mature Abies georgei var. smithii (Smith fir) growing at different elevations on the Tibet–Qinghai Plateau.Methods
Thin and fine roots (0·1–4·0 mm in diameter) were sampled at three different elevations (3480, 3900 and 4330 m, the last corresponding to the treeline). Tensile resistance of roots of different diameter classes was measured along with holocellulose and non-structural carbon (NSC) content.Key Results
The mean force necessary to break roots in tension decreased significantly with increasing altitude and was attributed to a decrease in holocellulose content. Holocellulose was significantly lower in roots at the treeline (29·5 ± 1·3 %) compared with those at 3480 m (39·1 ± 1·0 %). Roots also differed significantly in NSC, with 35·6 ± 4·1 mg g−1 dry mass of mean total soluble sugars in roots at 3480 m and 18·8 ± 2·1 mg g−1 dry mass in roots at the treeline.Conclusions
Root mechanical resistance, holocellulose and NSC content all decreased with increasing altitude. Holocellulose is made up principally of cellulose, the biosynthesis of which depends largely on NSC supply. Plants synthesize cellulose when conditions are optimal and NSC is not limiting. Thus, cellulose synthesis in the thin and fine roots measured in our study is probably not a priority in mature trees growing at very high altitudes, where climatic factors will be limiting for growth. Root NSC stocks at the treeline may be depleted through over-demand for carbon supply due to increased fine root production or winter root growth. 相似文献7.
Background and Aims
Molecular experiments suggest that the regulation of the biosynthesis of condensed tannin (CT) is sensitive to the presence of plant enemies. The enemy-specific response of CT concentrations to simulated attacks by pathogenic fungi, bacteria or herbivores was studied in Onobrychis viciifolia grown at four levels of nutrient availability. It was hypothesized that CT concentrations increase in response to an attack, and that constitutive and induced levels of CT are higher at low than at high nutrient availability. Investment in CT was also predicted to be negatively related to plant growth.Methods
Recently discovered substances by which plants recognize their opponents (i.e. elicitors) were used to simulate attacks to Onobrychis viciifolia grown at 0·0027, 0·075, 0·67 or 2 mm phosphorus in the nutrient solution.Key Results
Relative growth rate and final biomass (P < 0·001) were highest at 0·67 mm of phosphorus. CT concentrations decreased with increasing phosphorus availability, from 94·9 to 69·0 mg g−1 leaf dry weight (P < 0·001). Compared with unscathed plants, sterile mere mechanical wounding reduced tannin concentrations from 83·8 to 69·3 mg g−1 leaf dry weight (P < 0·01). Local CT concentrations were higher when wounded leaves were additionally treated with fungal (+15·9 %), bacterial (+19·6 %) or insect (+31·0 %) elicitors (each elicitor; P < 0·05); however, only the insect elicitor (saliva of the lepidopteron Spodoptera littoralis) induced CT concentrations higher than those of unscathed leaves.Conclusions
CT concentrations were inducible in the vicinity of the wound but the level of induction was unrelated to the nutrient status of the plant. There was no evidence of a growth-defence trade-off. The inverse relathionship between CT concentrations and nutrient availability appears to reflect passive growth dilution at high nutrient availability, rather than surplus CT production at low nutrient availability.Key words: Onobrychis viciifolia, condensed tannin, elicitor, plant–herbivore interaction, plant–pathogen interaction, growth–defence trade-off, Spodoptera littoralis, volicitin, Pen, chitin, elf18, flg22 相似文献8.
Background and Aims
Ptilotus polystachyus (green mulla mulla; ptilotus) is a short-lived perennial herb that occurs widely in Australia in arid and semi-arid regions with nutrient poor soils. As this species shows potential for domestication, its response to addition of phosphorus (P) and nitrogen (N) was compared to a variety of the domesticated exotic perennial pasture herb Cichorium intybus (chicory), ‘Puna’.Methods
Pots were filled with 3 kg of an extremely nutrient-deficient sterilized field soil that contained 3 mg kg−1 mineral N and 2 mg kg−1 bicarbonate-extractable P. The growth and P and N accumulation of ptilotus and chicory in response to seven rates of readily available phosphorus (0–300 mg P pot−1) and nitrogen (N) (0–270 mg N pot−1) was examined.Key Results
Ptilotus grew extremely well under low P conditions: shoot dry weights were 23, 6 and 1·7 times greater than for chicory at the three lowest levels of P addition, 0, 15 and 30 mg P pot−1, respectively. Ptilotus could not downregulate P uptake. Concentrations of P in shoots approached 4 % of dry weight and cryo-scanning electron microscopy and X-ray microanalysis showed 35–196 mm of P in cell vacuoles in a range of tissues from young leaves. Ptilotus had a remarkable tolerance of high P concentrations in shoots. While chicory exhibited symptoms of P toxicity at the highest rate of P addition (300 mg P pot−1), no symptoms were present for ptilotus. The two species responded in a similar manner to addition of N.Conclusions
In comparison to chicory, ptilotus demonstrated an impressive ability to grow well under conditions of low and high P availability. Further study of the mechanisms of P uptake and tolerance in ptilotus is warranted.Key words: Phosphorus, nitrogen, hyperaccumulation, X-ray microanalysis, cell vacuole, Australian native plant, toxicity, domestication, phytoremediation, Ptilotus polystachyus, Cichorium intybus 相似文献9.
10.
Background and Aims
Previous work has shown that the entire photosynthetic light response curve, based on both Mitscherlich and Michaelis–Menten functions, could be predicted in an interspecific context through allometric relations linking the parameters of these functions to two static leaf traits: leaf nitrogen (N) content and leaf mass per area (LMA). This paper describes to what extent these allometric relations are robust to changes in soil fertility and the growth irradiance of the plants.Methods
Plants of 25 herbaceous species were grown under controlled conditions in factorial combinations of low/high soil fertility and low/high growth irradiance. Net photosynthetic rates per unit dry mass were measured at light intensities ranging from 0 to 700 µmol m−2 s−1 photosynthetically active radiation (PAR).Key Results
The differing growth environments induced large changes in N, LMA and in each of the parameter estimates of the Mitscherlich and Michaelis–Menten functions. However, the differing growth environments induced only small (although significant) changes in the allometric relationships linking N and LMA to the parameters of the two functions. As a result, 88 % (Mitcherlich) and 89 % (Michaelis–Menten) of the observed net photosynthetic rates over the full range of light intensities (0–700 µmol m−2 s−1 PAR) and across all four growth environments could be predicted using only N and LMA using the same allometric relations.Conclusions
These results suggest the possibility of predicting net photosynthetic rates in nature across species over the full range of light intensities using readily available data. 相似文献11.
Change in uptake, transport and accumulation of ions in Nerium oleander (rosebay) as affected by different nitrogen sources and salinity 总被引:1,自引:0,他引:1
Background and Aims
The source of nitrogen plays an important role in salt tolerance of plants. In this study, the effects of NaCl on net uptake, accumulation and transport of ions were investigated in Nerium oleander with ammonium or nitrate as the nitrogen source in order to analyse differences in uptake and cycling of ions within plants.Methods
Plants were grown in a greenhouse in hydroponics under different salt treatments (control vs. 100 mm NaCl) with ammonium or nitrate as the nitrogen source, and changes in ion concentration in plants, xylem sap exuded from roots and stems, and phloem sap were determined.Key Results
Plant weight, leaf area and photosynthetic rate showed a higher salt tolerance of nitrate-fed plants compared with that of ammonium-fed plants. The total amount of Na+ transported in the xylem in roots, accumulated in the shoot and retranslocated in the phloem of ammonium-fed plants under salt treatment was 1·8, 1·9 and 2·7 times more, respectively, than that of nitrate-treated plants. However, the amount of Na+ accumulated in roots in nitrate-fed plants was about 1·5 times higher than that in ammonium-fed plants. Similarly, Cl− transport via the xylem to the shoot and its retranslocation via the phloem (Cl− cycling) were far greater with ammonium treatment than with nitrate treatment under conditions of salinity. The uptake and accumulation of K+ in shoots decreased more due to salinity in ammonium-fed plants compared with nitrate-fed plants. In contrast, K+ cycling in shoots increased due to salinity, with higher rates in the ammonium-treated plants.Conclusions
The faster growth of nitrate-fed plants under conditions of salinity was associated with a lower transport and accumulation of Na+ and Cl− in the shoot, whereas in ammonium-fed plants accumulation and cycling of Na+ and Cl− in shoots probably caused harmful effects and reduced growth of plants.Key words: Mineral cycling, Nerium oleander, nitrogen source, salinity, xylem and phloem transport 相似文献12.
Background
TRPV6 ion channels are key mediators of regulated transepithelial absorption of Ca2+ within the small intestine. Trpv6 -/- mice were reported to have lower bone density than wild-type littermates and significant disturbances in calcium homeostasis that suggested a role for TRPV6 in osteoblasts during bone formation and mineralization. TRPV6 and molecules related to transepithelial Ca2+ transport have been reported to be expressed at high levels in human and mouse osteoblasts.Results
Transmembrane ion currents in whole cell patch clamped SaOS-2 osteoblasts did not show sensitivity to ruthenium red, an inhibitor of TRPV5/6 ion channels, and 45Ca uptake was not significantly affected by ruthenium red in either SaOS-2 (P = 0.77) or TE-85 (P = 0.69) osteoblastic cells. In contrast, ion currents and 45Ca uptake were both significantly affected in a human bronchial epithelial cell line known to express TRPV6. TRPV6 was expressed at lower levels in osteoblastic cells than has been reported in some literature. In SaOS-2 TRPV6 mRNA was below the assay detection limit; in TE-85 TRPV6 mRNA was detected at 6.90±1.9 × 10−5 relative to B2M. In contrast, TRPV6 was detected at 7.7±3.0 × 10−2 and 2.38±0.28 × 10−4 the level of B2M in human carcinoma-derived cell lines LNCaP and CaCO-2 respectively. In murine primary calvarial osteoblasts TRPV6 was detected at 3.80±0.24 × 10−5 relative to GAPDH, in contrast with 4.3±1.5 × 10−2 relative to GAPDH in murine duodenum. By immunohistochemistry, TRPV6 was expressed mainly in myleocytic cells of the murine bone marrow and was observed only at low levels in murine osteoblasts, osteocytes or growth plate cartilage.Conclusions
TRPV6 is expressed only at low levels in osteoblasts and plays little functional role in osteoblastic calcium uptake. 相似文献13.
Background and Aims
Aluminium (Al) toxicity is one of the most severe limitations to crop production in acid soils. Inhibition of root elongation is the primary symptom of Al toxicity. However, the underlying basis of the process is unclear. Considering the multiple physiological and biochemical functions of pectin in plants, possible involvement of homogalacturonan (HG), one of the pectic polysaccharide domains, was examined in connection with root growth inhibition induced by Al.Methods
An immunolabelling technique with antibodies specific to HG epitopes (JIM5, unesterified residues flanked by methylesterifed residues; JIM7, methyl-esterified residues flanked by unesterified residues) was used to visualize the distribution of different types of HG in cell walls of root apices of two maize cultivars differing in Al resistance.Key Results
In the absence of Al, the JIM5 epitope was present around the cell wall with higher fluorescence intensity at cell corners lining the intercellular spaces, and the JIM7 epitope was present throughout the cell wall. However, treatment with 50 µm Al for 3 h produced 10 % root growth inhibition in both cultivars and caused the disappearance of fluorescence in the middle lamella of both epitopes. Prolonged Al treatment (24 h) with 50 % root growth inhibition in ‘B73’, an Al-sensitive cultivar, resulted in faint and irregular distribution of both epitopes. In ‘Nongda3138’, an Al-resistant cultivar, the distribution of HG epitopes was also restricted to the lining of intercellular spaces when a 50 % inhibition to root growth was induced by Al (100 µm Al, 9 h). Altered distribution of both epitopes was also observed when of roots were exposed to 50 µm LaCl3 for 24 h, resulting in 40 % inhibition of root growth.Conclusions
Changes in HG distribution and root growth inhibition were highly correlated, indicating that Al-induced perturbed distribution of HG epitopes is possibly involved in Al-induced inhibition of root growth in maize.Key words: Al toxicity, cell wall, homogalacturnonan, immunofluorescence, methylesterification, pectin 相似文献14.
Stefania Danko Takashi Daiho Kazuo Yamasaki Xiaoyu Liu Hiroshi Suzuki 《The Journal of biological chemistry》2009,284(34):22722-22735
As a stable analog for ADP-sensitive phosphorylated intermediate of sarcoplasmic reticulum Ca2+-ATPase E1PCa2·Mg, a complex of E1Ca2·BeFx, was successfully developed by addition of beryllium fluoride and Mg2+ to the Ca2+-bound state, E1Ca2. In E1Ca2·BeFx, most probably E1Ca2·BeF3−, two Ca2+ are occluded at high affinity transport sites, its formation required Mg2+ binding at the catalytic site, and ADP decomposed it to E1Ca2, as in E1PCa2·Mg. Organization of cytoplasmic domains in E1Ca2·BeFx was revealed to be intermediate between those in E1Ca2·AlF4− ADP (transition state of E1PCa2 formation) and E2·BeF3−·(ADP-insensitive phosphorylated intermediate E2P·Mg). Trinitrophenyl-AMP (TNP-AMP) formed a very fluorescent (superfluorescent) complex with E1Ca2·BeFx in contrast to no superfluorescence of TNP-AMP bound to E1Ca2·AlFx. E1Ca2·BeFx with bound TNP-AMP slowly decayed to E1Ca2, being distinct from the superfluorescent complex of TNP-AMP with E2·BeF3−, which was stable. Tryptophan fluorescence revealed that the transmembrane structure of E1Ca2·BeFx mimics E1PCa2·Mg, and between those of E1Ca2·AlF4−·ADP and E2·BeF3−. E1Ca2·BeFx at low 50–100 μm Ca2+ was converted slowly to E2·BeF3− releasing Ca2+, mimicking E1PCa2·Mg → E2P·Mg + 2Ca2+. Ca2+ replacement of Mg2+ at the catalytic site at approximately millimolar high Ca2+ decomposed E1Ca2·BeFx to E1Ca2. Notably, E1Ca2·BeFx was perfectly stabilized for at least 12 days by 0.7 mm lumenal Ca2+ with 15 mm Mg2+. Also, stable E1Ca2·BeFx was produced from E2·BeF3− at 0.7 mm lumenal Ca2+ by binding two Ca2+ to lumenally oriented low affinity transport sites, as mimicking the reverse conversion E2P· Mg + 2Ca2+ → E1PCa2·Mg.Sarcoplasmic reticulum Ca2+-ATPase (SERCA1a),2 a representative member of the P-type ion transporting ATPases, catalyze Ca2+ transport coupled with ATP hydrolysis (Fig. 1) (1–9). The enzyme forms phosphorylated intermediates from ATP or Pi in the presence of Mg2+ (10–13). In the transport cycle, the enzyme is first activated by cooperative binding of two Ca2+ ions at high affinity transport sites (E2 to E1Ca2, steps 1–2) (14) and autophosphorylated at Asp351 with MgATP to form the ADP-sensitive phosphoenzyme (E1P, step 3), which reacts with ADP to regenerate ATP in the reverse reaction. Upon this E1P formation, the two bound Ca2+ are occluded in the transport sites (E1PCa2). Subsequent isomeric transition to the ADP-insensitive form (E2PCa2), i.e. loss of ADP sensitivity at the catalytic site, results in rearrangement of the Ca2+ binding sites to deocclude Ca2+, reduce the affinity, and open the lumenal gate, thus releasing Ca2+ into the lumen (E2P, steps 4–5). Finally Asp351-acylphosphate in E2P is hydrolyzed to form the Ca2+-unbound inactive E2 state (steps 6 and 7). Mg2+ bound at the catalytic site is required as a physiological catalytic cofactor in phosphorylation and dephosphorylation and thus for the transport cycle. The cycle is totally reversible, e.g. E2P can be formed from Pi in the presence of Mg2+ and absence of Ca2+, and subsequent Ca2+ binding at lumenally oriented low affinity transport sites of E2P reverses the Ca2+-releasing step and produces E1PCa2, which is then decomposed to E1Ca2 by ADP.Open in a separate windowFIGURE 1.Ca2+ transport cycle of Ca2+-ATPase.Various intermediate structural states in the transport cycle were fixed as their structural analogs produced by appropriate ligands such as AMP-PCP (non-hydrolyzable ATP analog) or metal fluoride compounds (phosphate analogs), and their crystal structures were solved at the atomic level (15–22). The three cytoplasmic domains, N, P, and A, largely move and change their organization state during the transport cycle, and the changes are coupled with changes in the transport sites. Most remarkably, in the change from E1Ca2·AlF4−·ADP (the transition state for E1PCa2 formation, E1PCa2·ADP·Mg‡) to E2·BeF3− (the ground state E2P·Mg) (23–25), the A domain largely rotates by more than 90° approximately parallel to the membrane plane and associates with the P domain, thereby destroying the Ca2+ binding sites, and opening the lumenal gate, thus releasing Ca2+ into the lumen (see Fig. 2). E1PCa2·Ca·AMP-PN formed by CaAMP-PNP without Mg2+ is nearly the same as E1Ca2·AlF4−·ADP and E1Ca2·CaAMP-PCP in their crystal structures (17, 18, 22).Open in a separate windowFIGURE 2.Structure of SERCA1a and its change during processing of phosphorylated intermediate. E1Ca2·AlF4−·ADP (the transition state analog for phosphorylation E1PCa2·ADP·Mg‡) and E2·BeF3− (the ground state E2P analog (25)) were obtained from the Protein Data Bank (PDB accession code 1T5T (17) and 2ZBE (21), respectively). Cytoplasmic domains N (nucleotide binding), P (phosphorylation), and A (actuator), and 10 transmembrane helices (M1–M10) are indicated. The arrows on the domains, M1′ and M2 (Tyr122) in E1Ca2·AlF4−·ADP, indicate their approximate motions predicted for E1PCa2·ADP·Mg‡ → E2P·Mg. The phosphorylation site Asp351, TGES184 of the A domain, Arg198 (tryptic T2 site) on the Val200 loop (DPR198AV200NQD) of the A domain, and Thr242 (proteinase K site) on the A/M3-linker are shown. Seven hydrophobic residues gather in the E2P state to form the Tyr122-hydrophobic cluster (Y122-HC); Tyr122/Leu119 on the top part of M2, Ile179/Leu180/Ile232 of the A domain, and Val705/Val726 of the P domain. The overall structure of E1Ca2·AlF4−·ADP is virtually the same as those of E1Ca2·CaAMP-PCP and E1PCa2·Ca·AMP-PN (17, 18, 22).Despite these atomic structures, yet unsolved is the structure of E1PCa2·Mg, the genuine physiological intermediate E1PCa2 with bound Mg2+ at the catalytic site without the nucleotide. Its stable structural analog has yet to be developed. E1PCa2·Mg is the major intermediate accumulating almost exclusively at steady state under physiological conditions. Its rate-limiting isomerization results in Ca2+ deocclusion/release producing E2P·Mg as a key event for Ca2+ transport. In E1Ca2·CaAMP-PCP, E1Ca2·AlF4−·ADP, and E1PCa2·Ca·AMP-PN, the N and P domains are cross-linked and strongly stabilized by the bound nucleotide and/or Ca2+ at the catalytic site, thus they are crystallized (17, 18, 22). Kinetically, E1PCa2·Ca formed with CaATP is markedly stabilized due to Ca2+ binding at the catalytic Mg2+ site, and its isomerization to E2P is strongly retarded in contrast to E1PCa2·Mg (26, 27). Thus, the bound Ca2+ at the catalytic Mg2+ site likely produces a significantly different structural state from that with bound Mg2+.Therefore, it is now essential to develop a genuine E1PCa2·Mg analog without bound nucleotide and thereby gain further insight into the structural mechanism in the Ca2+ transport process. It is also crucial to further clarify the structural importance of Mg2+ as the physiological catalytic cation. In this study, we successfully developed the complex E1Ca2·BeFx, most probably E1Ca2·BeF3−, as the E1PCa2·Mg analog by adding beryllium fluoride (BeFx) to the E1Ca2 state without any nucleotides. For its formation, Mg2+ binding at the catalytic site was required and Ca2+ substitution for Mg2+ was absolutely unfavorable, revealing a likely structural reason for its preference as the physiological cofactor. In E1Ca2·BeF3−, two Ca2+ ions bound at the high affinity transport sites are occluded. It was also produced from E2·BeF3− by lumenal Ca2+ binding at the lumenally oriented low affinity transport sites, mimicking E2P·Mg + 2Ca2+ → E1PCa2·Mg. All properties of the newly developed E1Ca2·BeF3− fulfilled the requirements as the E1PCa2·Mg analog, and hence we were able to uncover the hitherto unknown nature of E1PCa2·Mg as well as structural events occurring in the phosphorylation and isomerization processes. Also, we successfully found the conditions that perfectly stabilize the E1Ca2·BeF3− complex. 相似文献
15.
Background and Aims
A common response of wetland plants to flooding is the formation of aquatic adventitious roots. Observations of aquatic root growth are widespread; however, controlled studies of aquatic roots of terrestrial herbaceous species are scarce. Submergence tolerance and aquatic root growth and physiology were evaluated in two herbaceous, perennial wetland species Cotula coronopifolia and Meionectes brownii.Methods
Plants were raised in large pots with ‘sediment’ roots in nutrient solution and then placed into individual tanks and shoots were left in air or submerged (completely or partially). The effects on growth of aquatic root removal, and of light availability to submerged plant organs, were evaluated. Responses of aquatic root porosity, chlorophyll and underwater photosynthesis, were studied.Key Results
Both species tolerated 4 weeks of complete or partial submergence. Extensive, photosynthetically active, aquatic adventitious roots grew from submerged stems and contributed up to 90 % of the total root dry mass. When aquatic roots were pruned, completely submerged plants grew less and had lower stem and leaf chlorophyll a, as compared with controls with intact roots. Roots exposed to the lowest PAR (daily mean 4·7 ± 2·4 µmol m−2 s−1) under water contained less chlorophyll, but there was no difference in aquatic root biomass after 4 weeks, regardless of light availability in the water column (high PAR was available to all emergent shoots).Conclusions
Both M. brownii and C. coronopifolia responded to submergence with growth of aquatic adventitious roots, which essentially replaced the existing sediment root system. These aquatic roots contained chlorophyll and were photosynthetically active. Removal of aquatic roots had negative effects on plant growth during partial and complete submergence. 相似文献16.
Background and Aims
Vascular epiphytes have to acquire nutrients from atmospheric wash out, stem-flow, canopy soils and trapped litter. Physiological studies on the adaptations to nutrient acquisition and plant utilization of nutrients have focused on phosphorus and nitrogen; potassium, as a third highly abundant nutrient element, has received minor attention. In the present study, potassium uptake kinetics by leaves, within-plant distribution and nutrient accumulation were analysed to gain an improved understanding of physiological adaptations to non-terrestrial nutrient supply of plants.Methods
Radioactively labelled 86RbCl was used as an analogue to study uptake kinetics of potassium absorbed from tanks of epiphytes, its plant distribution and the correlation between uptake efficiency and abundance of trichomes, functioning as uptake organs of leaves. Potassium in leaves was additionally analysed by atomic absorption spectroscopy to assess plant responses to potassium deficiency.Key Results
Labelled rubidium was taken up from tanks over a wide range of concentrations, 0·01–90 mm, which was achieved by two uptake systems. In four tank epiphytes, the high-affinity transporters had average Km values of 41·2 µm, and the low-affinity transporters average Km values of 44·8 mm. Further analysis in Vriesea splenriet showed that high-affinity uptake of rubidium was an ATP-dependent process, while low-affinity uptake was mediated by a K+-channel. The kinetic properties of both types of transporters are comparable with those of potassium transporters in roots of terrestrial plants. Specific differences in uptake velocities of epiphytes are correlated with the abundance of trichomes on their leaf surfaces. The main sinks for potassium were fully grown leaves. These leaves thus function as internal potassium sources, which allow growth to be maintained during periods of low external potassium availability.Conclusions
Vascular epiphytes possess effective mechanisms to take up potassium from both highly diluted and highly concentrated solutions, enabling the plant to incorporate this nutrient element quickly and almost quantitatively from tank solutions. A surplus not needed for current metabolism is stored, i.e. plants show luxury consumption. 相似文献17.
Background and Aims
Myxospermy is a term which describes the ability of a seed to produce mucilage upon hydration. The mucilage is mainly comprised of plant cell-wall polysaccharides which are deposited during development of those cells that comprise the seed coat (testa). Myxospermy is more prevalent among those plant species adapted to surviving on arid sandy soils, though its significance in determining the ecological fitness of plants is unclear. In this study, the first mathematical model of myxospermous seed mucilage expansion is presented based on seeds of the model plant species Capsella bursa-pastoris (shepherd''s purse).Methods
The structures underpinning the expansion process were described using light, electron and time-lapse confocal micrographs. The data and experimental observations were used to create a mathematical model of myxospermous seed mucilage expansion based on diffusion equations.Key Results
The mucilage expansion was rapid, taking 5 s, during which the cell mucilage volume increased 75-fold. At the level of the seed, this represented a 6-fold increase in seed volume and a 2·5-fold increase in seed surface area. These increases were shown to be a function of water uptake (16 g water g−1 mucilage dry weight), and relaxation of the polymers which comprised the mucilage. In addition, the osmotic pressure of the seed mucilage, estimated by assessing the mucilage expansion of seeds hydrated in solutions of varying osmotic pressure, was –0·54 MPa (equivalent to 0·11 m or 6·6 g L−1 NaCl).Conclusions
The results showed that the mucilage may be characterized as hydrogel and seed-mucilage expansion may be modelled using the diffusion equation described. The potential of myxospermous seeds to affect the ecological services provided by soil is discussed briefly. 相似文献18.
Proctor MC 《Annals of botany》2012,109(5):1019-1026
Background and Aims
Hymenophyllaceae (filmy ferns) are typically plants of shady, constantly moist habitats. They attain greatest species diversity and biomass in humid tropical montane forests and temperate hyperoceanic climates. This paper presents ecophysiological data bearing on their worldwide ecological niche space and its limits.Methods
Chlorophyll fluorescence was used to monitor recovery in desiccation experiments, and for measurements of 95 % saturating irradiance [photosynthetic photon flux density (PPFD95 %)] of photosynthetic electron flow and other parameters, in the New Zealand Hymenophyllum sanguinolentum, and three species each of Hymenophyllum and Trichomanes from forests in Trinidad and Venezuela.Key Results
Hymenophyllum sanguinolentum was comparable in desiccation tolerance and light responses with the European species. The more common species in the two tropical forests showed PPFD95 % >100 µmol m−2 s−1, and withstood moderate desiccation (–40 MPa) for several days. The four most shade-adapted species had PPFD95 % ≤51 µmol m−2 s−1, and were sensitive to even mild and brief desiccation (–22 MPa for 3 d).Conclusions
Light and desiccation responses of filmy ferns can be seen as an integrated package. At low light and windspeed in humid forests, net radiation and saturation deficit are low, and diffusion resistance high. Water loss is slow and can be supported by modest conduction from the sub-stratum. With higher irradiance, selection pressure for desiccation tolerance increases progressively. With low light and high humidity, the filmy fern pattern of adaptation is probably optimal, and the vascular plant leaf with mesophyll and stomata offers no advantage in light capture, water economy or CO2 uptake. Trade-offs between light adaptation and desiccation tolerance, and between stem conduction and water absorption through the leaf surface, underlie adaptive radiation and niche differentiation of species within the family. Hymenophyllaceae are a rare example of an evolutionary shift of adaptive strategy from typical vascular plant adaptation to the poikilohydry most typical of bryophytes. 相似文献19.
Bustos D Lascano R Villasuso AL Machado E Senn ME Córdoba A Taleisnik E 《Annals of botany》2008,102(4):551-559
Background and Aims
Experimental evidence in the literature suggests that O2•− produced in the elongation zone of roots and leaves by plasma membrane NADPH oxidase activity is required for growth. This study explores whether growth changes along the root tip induced by hyperosmotic treatments in Zea mays are associated with the distribution of apoplastic O2•−.Methods
Stress treatments were imposed using 150 mm NaCl or 300 mm sorbitol. Root elongation rates and the spatial distribution of growth rates in the root tip were measured. Apoplastic O2•− was determined using nitro blue tetrazolium, and H2O2 was determined using 2′, 7′-dichlorofluorescin.Key Results
In non-stressed plants, the distribution of accelerating growth and highest O2•− levels coincided along the root tip. Salt and osmotic stress of the same intensity had similar inhibitory effects on root elongation, but O2•− levels increased in sorbitol-treated roots and decreased in NaCl-treated roots.Conclusions
The lack of association between apoplastic O2•− levels and root growth inhibition under hyper-osmotic stress leads us to hypothesize that under those conditions the role of apoplastic O2•− may be to participate in signalling processes, that convey information on the nature of the substrate that the growing root is exploring.Key words: Root tip growth, Zea mays, salt stress, reactive oxygen species, ROS 相似文献20.