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1.
Wild-type and antisense rbcS tobacco (Nicotiana tabacum) plants were grown in a glasshouse in midsummer in Portugal with an irradiance of 1500–2000 μmol m−2s−1 and daytime temperatures of 30–35 °C. The Rubisco content of the transformants was lower by 35, 80 and over 90% than that of the wild-type. Gas exchange was measured over three separate days. There was a near-linear relation between Rubisco content and photosynthetic rate during the period of high irradiance, allowing a flux control coefficient of 0.83–0.89 to be estimated. The relation deviated slightly from linearity, because the internal CO2 concentration (c;) was higher in the transformants than in the wild-type (190 and 275 μmol mol−1 in plants with 35 and 80% less Rubisco, respectively, compared with 175 μmol mol−1 for wild-type), compensating to some extent for the decreased Rubisco content. This increase in ci occurred because the stomatal conductance (g) remained unaltered or was even higher in plants with decreased Rubisco, despite the lower rate of CO2 assimilation. As a consequence, water use efficiency declined. The decreased rate of photosynthesis was not accompanied by a stoichiometric decrease in apparent growth rate. These results are discussed in relation to earlier studies of the plant set in growth cabinets. It is concluded that tobacco can adjust over a wide range of growth conditions to avoid a onesided limitation by Rubisco, but that in extreme environmental conditions this capacity to adapt is exhausted.  相似文献   

2.
Control coefficients were used to describe the degree to which ribulose bisphosphate carboxylase/oxygenase (Rubisco) limits the steady-state rate of CO2 assimilation in sunflower leaves from plants grown at high (800 μmol mol−1) and low (350 μmol mol−1) CO2. The magnitude of a control coefficient is approximately the percentage change in the flux that would result from a 1% rise in enzyme active site concentration. In plants grown at low CO2, leaves of different ages varied considerably in their photosynthetic capacities. In a saturating light flux and an ambient CO2 concentration of 350 μmol mol−1, the Rubisco control coefficient was about 0.7 in all leaves, indicating that Rubisco activity largely limited the assimilation flux. The Rubisco control coefficient for leaves grown at 350 μmol mol−1 CO2 dropped to about zero when the ambient CO2 concentration was raised to 800 μmol mol−1. In relatively young, fully expanded leaves of plants grown at high CO2, the Rubisco control coefficient was also about 0.7 at a saturating light flux and at the CO2 concentration at which the plants were grown (800 μmol mol−1). This apparently resulted from a decrease in the concentration of Rubisco active sites. In older leaves, however, the control coefficient was about 0.2. Because, on the whole, Rubisco activity still largely limits the assimilation flux in plants grown at high CO2, the kinetics of this enzyme can still be used to model photosynthesis under these conditions. The relatively high Rubisco control coefficient under enhanced CO2 indicates that the young sunflower leaves have the capacity to acclimate their photosynthetic biochemistry in a way consistent with an optimal use of protein resources.  相似文献   

3.
Tobacco (Nicotiana tabacum L.) plants transformed with antisense rbcS to decrease the expression of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) have been used to investigate the contribution of Rubisco to the control of photosynthesis in plants growing at different irradiances. Tobacco plants were grown in controlled-climate chambers under ambient CO2 at 20°C at 100, 300 and 750 mol·m–2·s–1 irradiance, and at 28°C at 100, 300 and 1000 mol·m–2·s–1 irradiance. (i) Measurement of photosynthesis under ambient conditions showed that the flux control coefficient of Rubisco (C infRubisco supA ) was very low (0.01–0.03) at low growth irradiance, and still fairly low (0.24–0.27) at higher irradiance. (ii) Short-term changes in the irradiance used to measure photosynthesis showed that C infRubisco supA increases as incident irradiance rises, (iii) When low-light (100 mol·m–2·s–1)-grown plants are exposed to high (750–1000 mol·m–2·s–1) irradiance, Rubisco is almost totally limiting for photosynthesis in wild types. However, when high-light-grown leaves (750–1000 mol·m–2·s–1) are suddenly exposed to high and saturating irradiance (1500–2000 mol·m–2·s–1), C infRubisco supA remained relatively low (0.23–0.33), showing that in saturating light Rubisco only exerts partial control over the light-saturated rate of photosynthesis in sun leaves; apparently additional factors are co-limiting photosynthetic performance, (iv) Growth of plants at high irradiance led to a small decrease in the percentage of total protein found in the insoluble (thylakoid fraction), and a decrease of chlorophyll, relative to protein or structural leaf dry weight. As a consequence of this change, high-irradiance-grown leaves illuminated at growth irradiance avoided an inbalance between the light reactions and Rubisco; this was shown by the low value of C infRubisco supA (see above) and by measurements showing that non-photochemical quenching was low, photochemical quenching high, and NADP-malate dehydrogenase activation was low at the growth irradiance. In contrast, when a leaf adapted to low irradiance was illuminated at a higher irradiance, Rubisco exerted more control, non-photochemical quenching was higher, photochemical quenching was lower, and NADP-malate dehydrogenase activation was higher than in a leaf which had grown at that irradiance. We conclude that changes in leaf composition allow the leaf to avoid a one-sided limitation by Rubisco and, hence, overexcitation and overreduction of the thylakoids in high-irradiance growth conditions, (v) Antisense plants with less Rubisco contained a higher content of insoluble (thylakoid) protein and chlorophyll, compared to total protein or structural leaf dry weight. They also showed a higher rate of photosynthesis than the wild type, when measured at an irradiance below that at which the plant had grown. We propose that N-allocation in low light is not optimal in tobacco and that genetic manipulation to decrease Rubisco may, in some circumstances, increase photosynthetic performance in low light.Abbreviations A rate of photosynthesis - C infRubisco supA flux control coefficient of Rubisco for photosynthesis - ci internal CO2 concentration - qE energy-dependent quenching of chlorophyll fluorescense - qQ photochemical quenching of chlorophyll fluorescence - NADP-MDH NADP-dependent malate dehydrogenase - Rubisco ribulose-1,5-bisphosphate carboxylase-oxygenase - RuBP ribulose-1,5-bisphosphate This work was supported by the Deutsche Forschungsgemeinschaft (SFB 137).  相似文献   

4.
Nuphar lutea is an amphibious plant with submerged and aerial foliage, which raises the question how do both leaf types perform photosynthetically in two different environments. We found that the aerial leaves function like terrestrial sun-leaves in that their photosynthetic capability was high and saturated under high irradiance (ca. 1,500 μmol photons m−2 s−1). We show that stomatal opening and Rubisco activity in these leaves co-limited photosynthesis at saturating irradiance fluctuating in a daily rhythm. In the morning, sunlight stimulated stomatal opening, Rubisco synthesis, and the neutralization of a night-accumulated Rubisco inhibitor. Consequently, the light-saturated quantum efficiency and rate of photosynthesis increased 10-fold by midday. During the afternoon, gradual closure of the stomata and a decrease in Rubisco content reduced the light-saturated photosynthetic rate. However, at limited irradiance, stomatal behavior and Rubisco content had only a marginal effect on the photosynthetic rate, which did not change during the day. In contrast to the aerial leaves, the photosynthesis rate of the submerged leaves, adapted to a shaded environment, was saturated under lower irradiance. The light-saturated quantum efficiency of these leaves was much lower and did not change during the day. Due to their low photosynthetic affinity for CO2 (35 μM) and inability to utilize other inorganic carbon species, their photosynthetic rate at air-equilibrated water was CO2-limited. These results reveal differences in the photosynthetic performance of the two types of Nuphar leaves and unravel how photosynthetic daily rhythm in the aerial leaves is controlled.  相似文献   

5.
Following an increase in photon flux density (PFD), ribulose bisphosphate carboxylase/oxygenase (Rubisco) undergoes a slow activation which substantially limits the rate of photosynthesis. This activation process is mediated in part by Rubisco activase. Antisense DNA plants of tobacco were used to quantify the degree to which activase limits Rubisco activation. Reductions in leaf activase content caused proportional reductions in the rate of Rubisco activation following a PFD increase from 110 to 1200 micromol m(-2) sec(-1). This was the case for activase levels up to and slightly beyond normal wild-type activase levels. Activase therefore has a flux control coefficient of unity with respect to the Rubisco activation flux. Such a high control coefficient has rarely been measured for any metabolic system, and this is the highest control coefficient measured for an important photosynthetic flux. In contrast, the rate of Rubisco inactivation in leaves following a drop in PFD of 1200 to 110 micromol m(-2) sec(-1) was unchanged by a 60% reduction in activase levels. Despite the high degree of control that activase exerts over the rate of activation, and thus non-steady-state photosynthesis, it was shown that steady-state photosynthesis was largely unaffected by activase concentration until it was reduced below approximately 15% of the wild-type level. The significance of these results and their implications for published models of Rubisco activation are discussed.  相似文献   

6.
Factors that contribute to interspecific variation in photosynthetic nitrogen-use efficiency (PNUE, the ratio of CO2 assimilation rate to leaf organic nitrogen content) were investigated, comparing ten dicotyledonous species that differ inherently in specific leaf area (SLA, leaf area:leaf dry mass). Plants were grown hydroponically in controlled environment cabinets at two irradiances (200 and 1000 μmol m–2 s–1). CO2 and irradiance response curves of photosynthesis were measured followed by analysis of the chlorophyll, Rubisco, nitrate and total nitrogen contents of the leaves. At both irradiances, SLA ranged more than twofold across species. High-SLA species had higher in situ rates of photosynthesis per unit leaf mass, but similar rates on an area basis. The organic N content per unit leaf area was lower for the high-SLA species and consequently PNUE at ambient light conditions (PNUEamb) was higher in those plants. Differences were somewhat smaller, but still present, when PNUE was determined at saturating irradiances (PNUEmax). An assessment was made of the relative importance of the various factors that underlay interspecific variation in PNUE. For plants grown under low irradiance, PNUEamb of high-SLA species was higher primarily due to their lower N content per unit leaf area. Low-SLA species clearly had an overinvestment in photosynthetic N under these conditions. In addition, high SLA-species allocated a larger fraction of organic nitrogen to thylakoids and Rubisco, which further increased PNUEamb. High-SLA species grown under high irradiance showed higher PNUEamb mainly due to a higher Rubisco specific activity. Other factors that contributed were again their lower contents of Norg per unit leaf area and a higher fraction of photosynthetic N in electron transport and Rubisco. For PNUEmax, differences between species in organic leaf nitrogen content per se were no longer important and higher PNUEmax of the high SLA species was due to a higher fraction of N in␣photosynthetic compounds (for low-light plants) and a higher Rubisco specific activity (for high-light grown plants). Received: 11 October 1997 / Accepted: 9 April 1998  相似文献   

7.
The effect of nitrogen supply during growth on the contribution of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco; EC 4.1.1.39) to the control of photosynthesis was examined in tobacco (Nicotiana tabacum L.). Transgenic plants transformed with antisense rbcS to produce a series of plants with a progressive decrease in the amount of Rubisco were used to allow the calculation of the flux-control coefficient of Rubisco for photosynthesis (CR). Several points emerged from the data: (i) The strength of Rubisco control of photosynthesis, as measured by CR, was altered by changes in the short-term environmental conditions. Generally, CR was increased in conditions of increased irradiance or decreased CO2. (ii) The amount of Rubisco in wild-type plants was reduced as the nitrogen supply during growth was reduced and this was associated with an increase in CR. This implied that there was a specific reduction in the amount of Rubisco compared with other components of the photosynthetic machinery. (iii) Plants grown with low nitrogen and which had genetically reduced levels of Rubisco had a higher chlorophyll content and a lower chlorophyll a/b ratio than wild-type plants. This indicated that the nitrogen made available by genetically reducing the amount of Rubisco had been re-allocated to other cellular components including light-harvesting and electron-transport proteins. It is argued that there is a luxury additional investment of nitrogen into Rubisco in tobacco plants grown in high nitrogen, and that Rubisco can also be considered a nitrogen-store, all be it one where the opportunity cost of the nitrogen storage is higher than in a non-functional storage protein (i.e. it allows for a slightly higher water-use efficiency and for photosynthesis to respond to temporarily high irradiance).Abbreviations CR flux control coefficient of Rubisco for photosynthesis - rbcS gene for the Rubisco small subunit - Rubisco ribulose-1,5-bisphosphate carboxylase-oxygenase W.P. Quick is grateful to Professor D.T. Clarkson (Department of Agricultural Sciences, University of Bristol, Long Ashton, UK) for pointing out the connection between stomatal conductance and nutrient availability. This work was supported by the Deutsche Forschungsgemeinschaft.  相似文献   

8.
Peanut (Arachis hypogaea L. cv. Florunner) was grown from seed sowing to plant maturity under two daytime CO2 concentrations ([CO2]) of 360 μmol mol−1 (ambient) and 720 μmol mol−1 (elevated) and at two temperatures of 1.5 and 6.0 °C above ambient temperature. The objectives were to characterize peanut leaf photosynthesis responses to long-term elevated growth [CO2] and temperature, and to assess whether elevated [CO2] regulated peanut leaf photosynthetic capacity, in terms of activity and protein content of ribulose bisphosphate carboxylase-oxygenase (Rubisco), Rubisco photosynthetic efficiency, and carbohydrate metabolism. At both growth temperatures, leaves of plants grown under elevated [CO2] had higher midday photosynthetic CO2 exchange rate (CER), lower transpiration and stomatal conductance and higher water-use efficiency, compared to those of plants grown at ambient [CO2]. Both activity and protein content of Rubisco, expressed on a leaf area basis, were reduced at elevated growth [CO2]. Declines in Rubisco under elevated growth [CO2] were 27–30% for initial activity, 5–12% for total activity, and 9–20% for protein content. Although Rubisco protein content and activity were down-regulated by elevated [CO2], Rubisco photosynthetic efficiency, the ratio of midday light-saturated CER to Rubisco initial or total activity, of the elevated-[CO2] plants was 1.3- to 1.9-fold greater than that of the ambient-[CO2] plants at both growth temperatures. Leaf soluble sugars and starch of plants grown at elevated [CO2] were 1.3- and 2-fold higher, respectively, than those of plants grown at ambient [CO2]. Under elevated [CO2], leaf soluble sugars and starch, however, were not affected by high growth temperature. In contrast, high temperature reduced leaf soluble sugars and starch of the ambient-[CO2] plants. Activity of sucrose-P synthase, but not adenosine 5′-diphosphoglucose pyrophosphorylase, was up-regulated under elevated growth [CO2]. Thus, in the absence of other environmental stresses, peanut leaf photosynthesis would perform well under rising atmospheric [CO2] and temperature as predicted for this century.  相似文献   

9.
Transgenic tobacco (Nicotiana tabacum L.) plants transformed with antisense rbcS to produce a series of plants with a progressive decrease in the amount of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) have been used to investigate the contribution of Rubsico to the control of photosynthesis at different irradiance, CO2 concentrations and vapour-pressure deficits. Assimilation rates, transpiration, the internal CO2 concentration and chlorophyll fluorescence were measured in each plant. (i) The flux-control coefficient of Rubisco was estimated from the slope of the plot of Rubisco content versus assimilation rate. The flux-control coefficient had a value of 0.8 or more in high irradiance, (1050 mol·m–2·s–1), low-vapour pressure deficit (4 mbar) and ambient CO2 (350 bar). Control was marginal in enhanced CO2 (450 bar) or low light (310 mol·m–2·s–1) and was also decreased at high vapour-pressure deficit (17 mbar). No control was exerted in 5% CO2. (ii) The flux-control coefficients of Rubisco were compared with the fractional demand placed on the calculated available Rubisco capacity. Only a marginal control on photosynthetic flux is exerted by Rubisco until over 50% of the available capacity is being used. Control increases as utilisation rises to 80%, and approaches unity (i.e. strict limitation) when more than 80% of the available capacity is being used. (iii) In low light, plants with reduced Rubisco have very high energy-dependent quenching of chlorophyll fluorescence (qE) and a decreased apparent quantum yield. It is argued that Rubisco still exerts marginal control in these conditions because decreased Rubisco leads to increased thylakoid energisation and high-energy dependent dissipation of light energy, and lower light-harvesting efficiency. (iv) The flux-control coefficient of stomata for photosynthesis was calculated from the flux-control coefficient of Rubisco and the internal CO2 concentration, by applying the connectivity theorem. Control by the stomata varies between zero and about 0.25. It is increased by increased irradiance, decreased CO2 or decreased vapour-pressure deficit. (v) Photosynthetic oscillations in saturating irradiance and CO2 are suppressed in decreased-activity transformants before the steady-state rate of photosynthesis is affected. This provides direct evidence that these oscillations reveal the presence of excess Rubisco. (vi) Comparison of the flux-control coefficients of Rubisco with mechanistic models of photosynthesis provides direct support for the reliability of these models in conditions where Rubisco has a flux-control coefficient approach unity (i.e. limits photosynthesis), but also indicates that these models are less useful in conditions where control is shared between Rubisco and other components of the photosynthetic apparatus.Abbreviations A assimilation rate - Ci intercellular CO2 concentration in the leaf - CR flux-control coefficient of Rubisco for photosynthesis - qE high-energy-state-dependent quenching of chlorophyll fluorescence - QA primary acceptor of PSII - rbc S gene for the nuclear-encoded small subunit of Rubisco - Rubisco ribulose-1,5-bisphosphate carboxylase-oxygenase - Ru1,5bisP ribulose-1,5-bisphosphate - VPD vapour-pressure deficit  相似文献   

10.
Photosynthesis and growth to maturity of antisense ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activase Arabidopsis thaliana with reduced concentrations of activase relative to wild-type (Wt) plants were measured under low (200 mumol m-2 s-1) and high (600 mumol m-2 s-1) photosynthetic photon flux density growing conditions. Both growth and photosynthesis were significantly reduced in an Arabidopsis clone (R100) with 30 to 40% Wt activase, an effect that was more pronounced in high light. The aboveground biomass of the antisense clone R100 reached 80% of Wt under low light and 65% of Wt under high light. Decreased growth in the antisense plants was attributed to reduced relative rates of growth and leaf area expansion early in development; all plants attained similar values of relative rates of growth and leaf elongation by 21 d after planting. Reductions in photosynthesis were attributed to decreased Rubisco activation in the antisense plants. Rubisco constituted about 40% of total soluble protein in both Wt and clone R100 under both light regimes. Activase content was 5% and 1.4% of total soluble protein in Wt and clone R100, respectively, and also was unaffected by growth irradiance. The stoichiometry of Rubisco to activase was estimated at 20 Rubisco active sites per activase tetramer in Wt Arabidopsis and 60 to 80 in the transgenic clone R100. We conclude that Wt Arabidopsis does not contain Rubisco activase in great excess of the amount required for optimal growth.  相似文献   

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