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1.
Photosynthetic carbon gain in plants using the C3 photosynthetic pathway is substantially inhibited by photorespiration in warm environments, particularly in atmospheres with low CO2 concentrations. Unlike C4 plants, C3 plants are thought to lack any mechanism to compensate for the loss of photosynthetic productivity caused by photorespiration. Here, for the first time, we demonstrate that the C3 plants rice and wheat employ a specific mechanism to trap and reassimilate photorespired CO2. A continuous layer of chloroplasts covering the portion of the mesophyll cell periphery that is exposed to the intercellular air space creates a diffusion barrier for CO2 exiting the cell. This facilitates the capture and reassimilation of photorespired CO2 in the chloroplast stroma. In both species, 24–38% of photorespired and respired CO2 were reassimilated within the cell, thereby boosting photosynthesis by 8–11% at ambient atmospheric CO2 concentration and 17–33% at a CO2 concentration of 200 µmol mol?1. Widespread use of this mechanism in tropical and subtropical C3 plants could explain why the diversity of the world's C3 flora, and dominance of terrestrial net primary productivity, was maintained during the Pleistocene, when atmospheric CO2 concentrations fell below 200 µmol mol?1.  相似文献   

2.
SAMISH  Y.; KOLLER  D. 《Annals of botany》1968,32(4):687-694
An estimate of photorespiration is obtained from the relationshipbetween the net exchange of CO2 of the leaf and the internalCO2 concentration, i.e. within the mesophyll intercellular spaces.The latter is obtained by calculation, taking into account thecombined epidermal and boundary-layer resistances between thebulk atmosphere and the mesophyll intercellular spaces. Thelinear part of this relationship (at low CO2 concentrations)is extrapolated to zero internal concentration, at which noneof the intercellular photorespired CO2 is available for reassimilation.The calculated output of CO2 under such conditions providesan estimate of photorespiration, but, by failing to take intoaccount intracellular reassimilation of photorespired CO2 underestimatesactual photorespiration. As the slope of this linear relationshiprepresents the mesophyll (intracellular) resistance to CO2 uptake,this procedure was used to recalculate published data on effectsof light intensity and of oxygen concentration on net photosynthesis.The analysis showed that increased oxygen concentration anddecreased light intensity reduced photosynthesis largely byincreasing mesophyll resistance to CO2 uptake. It is suggestedthat the CO2 compensation point () is a function of both photorespiration(L) and mesophyll resistance (rm): = L. rm.  相似文献   

3.
Photosynthetic and photorespiratory characteristics of flaveria species   总被引:2,自引:2,他引:0  
Ku MS  Wu J  Dai Z  Scott RA  Chu C  Edwards GE 《Plant physiology》1991,96(2):518-528
The genus Flaveria shows evidence of evolution in the mechanism of photosynthesis as its 21 species include C3, C3-C4, C4-like, and C4 plants. In this study, several physiological and biochemical parameters of photosynthesis and photorespiration were measured in 18 Flaveria species representing all the photosynthetic types. The 10 species classified as C3-C4 intermediates showed an inverse continuum in level of photorespiration and development of the C4 syndrome. This ranges from F. sonorensis with relatively high apparent photorespiration and lacking C4 photosynthesis to F. Among the intermediates, the photosynthetic CO2 compensation points at 30°C and 1150 micromoles quanta per square meter per second varied from 9 to 29 microbars. The values for the three C4-like species varied from 3 to 6 microbars, similar to those measured for the C4 species. The activities of the photorespiratory enzymes glycolate oxidase, hydroxypyruvate reductase, and serine hydroxymethyltransferase decreased progressively from C3 to C3-C4 to C4-like and C4 species. On the other hand, most intermediates had higher levels of phosphenolpyruvate carboxylase and NADP-malic enzyme than C3 species, but generally lower activities compared to C4-like and C4 species. The levels of these C4 enzymes are correlated with the degree of C4 photosynthesis, based on the initial products of photosynthesis. Another indication of development of the C4 syndrome in C3-C4 Flaveria species was their intermediate chlorophyll a/b ratios. The chlorophyll a/b ratios of the various Flaveria species are highly correlated with the degree of C4 photosynthesis suggesting that the photochemical machinery is progressively altered during evolution in order to meet the specific energy requirements for operating the C4 pathway. In the progression from C3 to C4 species in Flaveria, the CO2 compensation point decreased more rapidly than did the decrease in O2 inhibition of photosynthesis or the increase in the degree of C4 photosynthesis. These results suggest that the reduction in photorespiration during evolution occurred initially by refixation of photorespired CO2 and prior to substantive reduction in O2 inhibition and development of the C4 syndrome. However, further reduction in O2 inhibition in some intermediates and C4-like species is considered primarily due to the development of the C4 syndrome. Thus, the evolution of C3-C4 intermediate photosynthesis likely occurred in response to environmental conditions which limit the intercellular CO2 concentration first via refixation of photorespired CO2, followed by development of the C4 syndrome.  相似文献   

4.
Species in the Laxa group of Panicum have C3 or C3/C4 photosynthesis based on leaf anatomical and CO2 exchange characteristics. Hybrids were previously made between C3/C4 and C3 species in this group (RH Brown et al. 1985 Plant Physiol 77: 653-658). In this paper, CO2 exchange, morphological, and leaf anatomical characteristics of F2 or F5 progeny from colchicine-induced amphiploids of C3/C4 × C3 hybrids (Panicum milioides Nees ex Trin. [C3/C4] × Panicum laxum Mez [C3] and Panicum spathellosum Doell [C3/C4] × Panicum boliviense Hack. [C3]) were studied.

There were no differences found in morphology or physiology between the amphiploids and the F1 hybrids from which they were produced. In the segregating progeny, CO2 compensation concentration and photorespiration values typical of C3, but not of C3/C4 plants, were recovered. Progeny were found from both crosses which possessed O2 inhibition of apparent photosynthesis typical of the parents, and in the case of the P. milioides × P. laxum cross, leaf anatomy and overall plant morphology typical of the parents were observed in some progeny. The progeny were found to possess recombinations of various traits associated with reduced photorespiration, so that no correlation existed among O2 inhibition of apparent photosynthesis, CO2 compensation concentration, and leaf anatomical traits. One plant was especially noteworthy in possessing leaf anatomy typical of C3/C4 plants, but with CO2 exchange characteristics of C3 plants.

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5.
G. J. Collatz 《Planta》1977,134(2):127-132
The response of net photosynthesis and apparent light respiration to changes in [O2], light intensity, and drought stress was determined by analysis of net photosynthetic CO2 response curves. Low [O2] treatment resulted in a large reduction in the rate of photorespiratory CO2 evolution. Lightintensity levels influenced the maximum net photosynthetic rate at saturating [CO2]. These results indicate that [CO2], [O2] and light intensity affect the levels of substrates involved in the enzymatic reactions of photosynthesis and photorespiration. Intracellular resistance to CO2 uptake decreased in low [O2] and increased at low leaf water potentials. This response reflects changes in the efficiency with which photosynthetic and photorespiratory substrates are formed and utilized. Water stress had no effect on the CO2 compensation point or the [CO2] at which net photosynthesis began to saturate at high light intensity. The relationship between these data and recently published in-vitro kinetic measurements with ribulose-diphosphate carboxylase is discussed.Abbreviations C w intracellular CO2 concentration - F gross gross photosynthesis - F net net photosynthesis - I light intensity - R L light respiration rate - r c carboxylation resistance - r 8 leaf gas-phase resistance - r i intracellular resistance; to CO2 uptake - r t resistance to CO2 flux between the intercellular spaces and the carboxylation sites - T L leaf temperature - t leaf water potential - CO2 compensation point  相似文献   

6.
Increasing night-time temperatures are a major threat to sustaining global rice (Oryza sativa L.) production. A simultaneous increase in [CO2] will lead to an inevitable interaction between elevated [CO2] (e[CO2]) and high night temperature (HNT) under current and future climates. Here, we conducted field experiments to identify [CO2] responsiveness from a diverse indica panel comprising 194 genotypes under different planting geometries in 2016. Twenty-three different genotypes were tested under different planting geometries and e[CO2] using a free-air [CO2] enrichment facility in 2017. The most promising genotypes and positive and negative controls were tested under HNT and e[CO2] + HNT in 2018. [CO2] responsiveness, measured as a composite response index on different yield components, grain yield, and photosynthesis, revealed a strong relationship (R2 = 0.71) between low planting density and e[CO2]. The most promising genotypes revealed significantly lower (P < 0.001) impact of HNT in high [CO2] responsive (HCR) genotypes compared to the least [CO2] responsive genotype. [CO2] responsiveness was the major driver determining grain yield and related components in HCR genotypes with a negligible yield loss under HNT. A systematic investigation highlighted that active selection and breeding for [CO2] responsiveness can lead to maintained carbon balance and compensate for HNT-induced yield losses in rice and potentially other C3 crops under current and future warmer climates.

Active selection for carbon dioxide responsiveness in rice and other C3 crops can mitigate yield loss induced by high night temperature.  相似文献   

7.
Maize is one of the major cultivated crops of China, having a central role in ensuring the food security of the country. There has been a significant increase in studies of maize under interactive effects of elevated CO2 concentration ([CO2]) and other factors, yet the interactive effects of elevated [CO2] and increasing precipitation on maize has remained unclear. In this study, a manipulative experiment in Jinzhou, Liaoning province, Northeast China was performed so as to obtain reliable results concerning the later effects. The Open Top Chambers (OTCs) experiment was designed to control contrasting [CO2] i.e., 390, 450 and 550 µmol·mol−1, and the experiment with 15% increasing precipitation levels was also set based on the average monthly precipitation of 5–9 month from 1981 to 2010 and controlled by irrigation. Thus, six treatments, i.e. C550W+15%, C550W0, C450W+15%, C450W0, C390W+15% and C390W0 were included in this study. The results showed that the irrigation under elevated [CO2] levels increased the leaf net photosynthetic rate (P n) and intercellular CO2 concentration (C i) of maize. Similarly, the stomatal conductance (G s) and transpiration rate (T r) decreased with elevated [CO2], but irrigation have a positive effect on increased of them at each [CO2] level, resulting in the water use efficiency (WUE) higher in natural precipitation treatment than irrigation treatment at elevated [CO2] levels. Irradiance-response parameters, e.g., maximum net photosynthetic rate (P nmax) and light saturation points (LSP) were increased under elevated [CO2] and irrigation, and dark respiration (R d) was increased as well. The growth characteristics, e.g., plant height, leaf area and aboveground biomass were enhanced, resulting in an improved of yield and ear characteristics except axle diameter. The study concluded by reporting that, future elevated [CO2] may favor to maize when coupled with increasing amount of precipitation in Northeast China.  相似文献   

8.
A practical guide to calculating the mannitol (MAN) amendment required to achieve the desired water potential (Ψ) of polyethylene glycol/dextran (PEG/DEX) aqueous two-phase systems for protoplast purification is presented. The empirically generated equation Ψ = 305[PEG′]2[MAN] + 0.74[PEG′][MAN]T − 103[PEG′][MAN] + 5.6[PEG′]2T − 623[PEG′]2 − 0.25[PEG′]T + 12.7[PEG′] − 0.078[MAN]T − 22.75[MAN]accurately predicts experimental Ψ (in bars). [PEG′] indicates the presence of DEX where [DEX] = [PEG]/(0.6−0.4[PEG]). The equation is applicable for these ranges: [PEG′] from 0.047 to 0.13 gram per gram H2O; [MAN] from 0 to 0.7 molal; T from 4.5 to 40°C. Actual Ψ should differ from derived Ψ by no more than 8% for the least negative values to 4% for the most negative values. The Ψ for solutions of MAN, of PEG, and of DEX were also determined. Equations to fit data for each were generated. Analyses indicated a significant synergistic effect on Ψ when MAN is added to PEG/DEX and, at certain concentrations, between PEG and DEX.  相似文献   

9.
The submersed angiosperms Myriophyllum spicatum L. and Hydrilla verticillata (L.f.) Royal exhibited different photosynthetic pulse-chase labeling patterns. In Hydrilla, over 50% of the 14C was initially in malate and aspartate, but the fate of the malate depended upon the photorespiratory state of the plant. In low photorespiration Hydrilla, malate label decreased rapidly during an unlabeled chase, whereas labeling of sucrose and starch increased. In contrast, for high photorespiration Hydrilla, malate labeling continued to increase during a 2-hour chase. Thus, malate formation occurs in both photorespiratory states, but reduced photorespiration results when this malate is utilized in the light. Unlike Hydrilla, in low photorespiration Myriophyllum, 14C incorporation was via the Calvin cycle, and less than 10% was in C4 acids.

Ethoxyzolamide, a carbonic anhydrase inhibitor and a repressor of the low photorespiratory state, increased the label in glycolate, glycine, and serine of Myriophyllum. Isonicotinic acid hydrazide increased glycine labeling of low photorespiration Myriophyllum from 14 to 25%, and from 12 to 48% with high photorespiration plants. Similar trends were observed with Hydrilla. Increasing O2 increased the per cent [14C]glycine and the O2 inhibition of photosynthesis in Myriophyllum. In low photorespiration Myriophyllum, glycine labeling and O2 inhibition of photosynthesis were independent of the CO2 level, but in high photorespiration plants the O2 inhibition was competitively decreased by CO2. Thus, in low but not high photorespiration plants, glycine labeling and O2 inhibition appeared to be uncoupled from the external [O2]/[CO2] ratio.

These data indicate that the low photorespiratory states of Hydrilla and Myriophyllum are mediated by different mechanisms, the former being C4-like, while the latter resembles that of low CO2-grown algae. Both may require carbonic anhydrase to enhance the use of inorganic carbon for reducing photorespiration.

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10.
Mass spectrometric techniques were used to trace the incorporation of [18O]oxygen into metabolites of the photorespiratory pathway. Glycolate, glycine, and serine extracted from leaves of the C3 plants, Spinacia oleracea L., Atriplex hastata, and Helianthus annuus which had been exposed to [18O]oxygen at the CO2 compensation point were heavily labeled with 18O. In each case one, and only one of the carboxyl oxygens was labeled. The abundance of 18O in this oxygen of glycolate reached 50 to 70% of that of the oxygen provided after only 5 to 10 seconds exposure to [18O]oxygen. Glycine and serine attained the same final enrichment after 40 and 180 seconds, respectively. This confirms that glycine and serine are synthesized from glycolate.

The labeling of photorespiratory intermediates in intact leaves reached a mean of 59% of that of the oxygen provided in the feedings. This indicates that at least 59% of the glycolate photorespired is synthesized with the fixation of molecular oxygen. This estimate is certainly conservative owing to the dilution of labeled oxygen at the site of glycolate synthesis by photosynthetic oxygen. We examined the yield of 18O in glycolate synthesized in vitro by isolated intact spinach chloroplasts in a system which permitted direct sampling of the isotopic composition of the oxygen at the site of synthesis. The isotopic enrichment of glycolate from such experiments was 90 to 95% of that of the oxygen present during the incubation.

The carboxyl oxygens of 3-phosphoglycerate also became labeled with 18O in 20- and 40-minute feedings with [18O]oxygen to intact leaves at the CO2 compensation point. Control experiments indicated that this label was probably due to direct synthesis of 3-phosphoglycerate from glycolate during photorespiration. The mean enrichment of 3-phosphoglycerate was 14 ± 4% of that of glycine or serine, its precursors of the photorespiratory pathway, in 10 separate feeding experiments. It is argued that this constant dilution of label indicates a constant stoichiometric balance between photorespiratory and photosynthetic sources of 3-phosphoglycerate at the CO2 compensation point.

Oxygen uptake sufficient to account for about half of the rate of 18O fixation into glycine in the intact leaves was observed with intact spinach chloroplasts. Oxygen uptake and production by intact leaves at the CO2 compensation point indicate about 1.9 oxygen exchanged per glycolate photorespired. The fixation of molecular oxygen into glycolate plus the peroxisomal oxidation of glycolate to glyoxylate and the mitochondrial conversion of glycine to serine can account for up to 1.75 oxygen taken up per glycolate.

These studies provide new evidence which supports the current formulation of the pathway of photorespiration and its relation to photosynthetic metabolism. The experiments described also suggest new approaches using stable isotope techniques to study the rate of photorespiration and the balance between photorespiration and photosynthesis in vivo.

  相似文献   

11.
Lauer MJ  Boyer JS 《Plant physiology》1992,98(4):1310-1316
Observations of nonuniform photosynthesis across leaves cast doubt on internal CO2 partial pressures (pi) calculated on the assumption of uniformity and can lead to incorrect conclusions about the stomatal control of photosynthesis. The problem can be avoided by measuring pi directly because the assumptions of uniformity are not necessary. We therefore developed a method that allowed pi to be measured continuously in situ for days at a time under growth conditions and used it to investigate intact leaves of sunflower (Helianthus annuus L.), soybean (Glycine max L. Merr.), and bush bean (Phaseolus vulgaris L.) subjected to high or low leaf water potentials (ψw) or high concentrations of abscisic acid (ABA). The leaves maintained a relatively constant differential (Δp) between ambient CO2 and measured pi throughout the light period when water was supplied. When water was withheld, ψw decreased and the stomata began to close, but measured pi increased until the leaf reached a ψw of −1.76 (bush bean), −2.12 (sunflower) or −3.10 (soybean) megapascals, at which point Δp = 0. The increasing pi indicated that stomata did not inhibit CO2 uptake and a Δp of zero indicated that CO2 uptake became zero despite the high availability of CO2 inside the leaf. In contrast, when sunflower leaves at high ψw were treated with ABA, pi did not increase and instead decreased rapidly and steadily for up to 8 hours even as ψw increased, as expected if ABA treatment primarily affected stomatal conductance. The accumulating CO2 at low ψw and contrasting response to ABA indicates that photosynthetic biochemistry limited photosynthesis at low ψw but not at high ABA.  相似文献   

12.
Although climate scenarios have predicted an increase in [CO2] and temperature conditions, to date few experiments have focused on the interaction of [CO2] and temperature effects in wheat development. Recent evidence suggests that photosynthetic acclimation is linked to the photorespiration and N assimilation inhibition of plants exposed to elevated CO2. The main goal of this study was to analyze the effect of interacting [CO2] and temperature on leaf photorespiration, C/N metabolism and N transport in wheat plants exposed to elevated [CO2] and temperature conditions. For this purpose, wheat plants were exposed to elevated [CO2] (400 vs 700 µmol mol?1) and temperature (ambient vs ambient + 4°C) in CO2 gradient greenhouses during the entire life cycle. Although at the agronomic level, elevated temperature had no effect on plant biomass, physiological analyses revealed that combined elevated [CO2] and temperature negatively affected photosynthetic performance. The limited energy levels resulting from the reduced respiratory and photorespiration rates of such plants were apparently inadequate to sustain nitrate reductase activity. Inhibited N assimilation was associated with a strong reduction in amino acid content, conditioned leaf soluble protein content and constrained leaf N status. Therefore, the plant response to elevated [CO2] and elevated temperature resulted in photosynthetic acclimation. The reduction in transpiration rates induced limitations in nutrient transport in leaves of plants exposed to elevated [CO2] and temperature, led to mineral depletion and therefore contributed to the inhibition of photosynthetic activity.  相似文献   

13.
A transient CO2 burst is exhibited by irradiated leaves of the C3 plant geranium (Pelargonium X hortorum, Bailey) after the irradiance is quickly lowered. The light CO2 burst appears to be related to photorespiration because of its irradiance dependency and its sensitivity to other environmental components such as CO2 and O2 concentration. The term post-lower-irradiance CO2 burst or PLIB is used to describe the phenomenon. The PLIB appears to be a quantitative measurement of photorespiration with intact geranium leaves. The PLIB has been observed with intact leaves of other C3 plants but not with C4 leaves. Therefore, it is proposed that, after maximizing intact leaf photosynthetic rates and leaf chamber gas measuring conditions, photorespiration can be measured with intact C3 leaves such as geranium as a transient post-lower-irradiance CO2 burst.  相似文献   

14.
Brown RH  Byrd GT  Black CC 《Plant physiology》1992,100(2):947-950
Hybrids have been made between species of Flaveria exhibiting varying levels of C4 photosynthesis. The degree of C4 photosynthesis expressed in four interspecific hybrids (Flaveria trinervia [C4] × F. linearis [C3-C4], F. brownii [C4-like] × F. linearis, and two three-species hybrids from F. trinervia × [F. brownii × F. linearis]) was estimated by inhibiting phosphoenolpyruvate carboxylase in vivo with 3,3-dichloro-2-dihydroxyphosphinoylmethyl-2-propenoate (DCDP). The inhibitor was fed to detached leaves at a concentration of 4 mm, and apparent photosynthesis was measured at atmospheric levels of CO2 and at 20 and 210 mL L−1 of O2. Photosynthesis at 210 mL L−1 of O2 was inhibited 32% by DCDP in F. linearis, by 60% in F. brownii, and by 87% in F. trinervia. Inhibition in the hybrids ranged from 38 to 52%. The inhibition of photosynthesis by 210 mL L−1 of O2 was increased when DCDP was used, except in the C4 species, F. trinervia, in which photosynthesis was insensitive to O2. Except for F. trinervia, control plants with less O2 sensitivity (more C4-like) exhibited a progressively greater change in O2 inhibition of photosynthesis when treated with DCDP. This increased O2 inhibition probably resulted from decreased CO2 concentrations in bundle sheath cells due to inhibition of phosphoenolpyruvate carboxylase. The inhibition of photosynthesis by DCDP is concluded to underestimate the degree of C4 photosynthesis in the interspecific hybrids because increased direct assimilation of atmospheric CO2 by ribulose bisphosphate carboxylase may compensate for inhibition of phosphoenolpyruvate carboxylase.  相似文献   

15.
Respiration in the light (RL) releases CO2 in photosynthesizing leaves and is a phenomenon that occurs independently from photorespiration. Since RL lowers net carbon fixation, understanding RL could help improve plant carbon-use efficiency and models of crop photosynthesis. Although RL was identified more than 75 years ago, its biochemical mechanisms remain unclear. To identify reactions contributing to RL, we mapped metabolic fluxes in photosynthesizing source leaves of the oilseed crop and model plant camelina (Camelina sativa). We performed a flux analysis using isotopic labeling patterns of central metabolites during 13CO2 labeling time course, gas exchange, and carbohydrate production rate experiments. To quantify the contributions of multiple potential CO2 sources with statistical and biological confidence, we increased the number of metabolites measured and reduced biological and technical heterogeneity by using single mature source leaves and quickly quenching metabolism by directly injecting liquid N2; we then compared the goodness-of-fit between these data and data from models with alternative metabolic network structures and constraints. Our analysis predicted that RL releases 5.2 μmol CO2 g−1 FW h−1 of CO2, which is relatively consistent with a value of 9.3 μmol CO2 g−1 FW h−1 measured by CO2 gas exchange. The results indicated that ≤10% of RL results from TCA cycle reactions, which are widely considered to dominate RL. Further analysis of the results indicated that oxidation of glucose-6-phosphate to pentose phosphate via 6-phosphogluconate (the G6P/OPP shunt) can account for >93% of CO2 released by RL.  相似文献   

16.
Three allelic mutants of Arabidopsis thaliana which lack mitochondrial serine transhydroxymethylase activity due to a recessive nuclear mutation have been characterized. The mutants were shown to be deficient both in glycine decarboxylation and in the conversion of glycine to serine. Glycine accumulated as an end product of photosynthesis in the mutants, largely at the expense of serine, starch, and sucrose formation. The mutants photorespired CO2 at low rates in the light, but this evolution of photorespiratory CO2 was abolished by provision of exogenous NH3. Exogenous NH3 was required by the mutants for continued synthesis of glycine under photorespiratory conditions. These and related results with wild-type Arabidopsis suggested that glycine decarboxylation is the sole site of photorespiratory CO2 release in wild-type plants but that depletion of the amino donors required for glyoxylate amination may lead to CO2 release from direct decarboxylation of glyoxylate. Photosynthetic CO2 fixation was inhibited in the mutants under atmospheric conditions which promote photorespiration but could be partially restored by exogenous NH3. The magnitude of the NH3 stimulation of photosynthesis indicated that the increase was due to the suppression of glyoxylate decarboxylation. The normal growth of the mutants under nonphotorespiratory atmospheric conditions indicates that mitochondrial serine transhydroxymethylase is not required in C3 plants for any function unrelated to photorespiration.  相似文献   

17.
Global climate change is expected to affect how plants respond to their physical and biological environments. In this study, we examined the effects of elevated CO2 ([CO2]) and low soil moisture on the physiological responses of mountain maple (Acer spicatum L.) seedlings to light availability. The seedlings were grown at ambient (392 µmol mol−1) and elevated (784 µmol mol−1) [CO2], low and high soil moisture (M) regimes, at high light (100%) and low light (30%) in the greenhouse for one growing season. We measured net photosynthesis (A), stomatal conductance (g s), instantaneous water use efficiency (IWUE), maximum rate of carboxylation (V cmax), rate of photosynthetic electron transport (J), triose phosphate utilization (TPU)), leaf respiration (R d), light compensation point (LCP) and mid-day shoot water potential (Ψx). A and g s did not show significant responses to light treatment in seedlings grown at low soil moisture treatment, but the high light significantly decreased the C i/C a in those seedlings. IWUE was significantly higher in the elevated compared with the ambient [CO2], and the effect was greater at high than the low light treatment. LCP did not respond to the soil moisture treatments when seedlings were grown in high light under both [CO2]. The low soil moisture significantly reduced Ψx but had no significant effect on the responses of other physiological traits to light or [CO2]. These results suggest that as the atmospheric [CO2] rises, the physiological performance of mountain maple seedlings in high light environments may be enhanced, particularly when soil moisture conditions are favourable.  相似文献   

18.
Abstract. The photosynthetic responses to temperature in C3, C3-C4 intermediate, and C4 species in the genus Flaveria were examined in an effort to identify whether the reduced photorespiration rates characteristic of C3-C4 intermediate photosynthesis result in adaptive advantages at warm leaf temperatures. Reduced photorespiration rates were reflected in lower CO2 compensation points at all temperatures examined in the C3-C4 intermediate, Flaveria floridana, compared to the C3 species, F. cronquistii. The C3-C4 intermediate, F. floridana, exhibited a C3-like photosynthetic temperature dependence, except for relatively higher photosynthesis rates at warm leaf temperatures compared to the C3 species, F. cronquistii. Using models of C3 and C3-C4 intermediate photosynthesis, it was predicted that by recycling photorespired CO2 in bundle-sheath cells, as occurs in many C3-C4 intermediates, photosynthesis rates at 35°C could be increased by 28%, compared to a C3 plant. Without recycling photorespired CO2, it was calculated that in order to improve photosynthesis rates at 35°C by this amount in C3 plants, (1) intercellular CO2 partial pressures would have to be increased from 25 to 31 Pa, resulting in a 57% decrease in water-use efficiency, or (2) the activity of RuBP carboxylase would have to be increased by 32%, resulting in a 22% decrease in nitrogen-use efficiency. In addition to the recycling of photorespired CO2, leaves of F. floridana appear to effectively concentrate CO2 at the active site of RuBP carboxylase, increasing the apparent carboxylation efficiency per unit of in vitro RuBP carboxylase activity. The CO2-concentrating activity also appears to reduce the temperature sensitivity of the carboxylation efficiency in F. floridana compared to F. cronquistii. The carboxylation efficiency per unit of RuBP carboxylase activity decreased by only 38% in F. floridana, compared to 50% in F. cronquistii, as leaf temperature was raised from 25 to 35°C. The C3-C4 intermediate, F. ramosissima, exhibited a photosynthetic temperature temperature response curve that was more similar to the C4 species, F. trinervia, than the C3 species, F. cronquistii. The C4-like pattern is probably related to the advanced nature of C4-like biochemical traits in F. ramosissima The results demonstrate that reductions in photorespiration rates in C3-C4 intermediate plants create photosynthetic advantages at warm leaf temperatures that in C3 plants could only be achieved through substantial costs to water-use efficiency and/or nitrogen-use efficiency.  相似文献   

19.
The postillumination transient of CO2 exchange and its relation to photorespiration has been examined in leaf discs from tobacco (Nicotiana tabacum) and maize (Zea mays). Studies of the transients observed by infrared gas analysis at 1, 21, and 43% O2 in an open system were extended using the nonsteady state model described previously (Peterson and Ferrandino 1984 Plant Physiol 76: 976-978). Cumulative CO2 exchange equivalents (i.e. nanomoles CO2) versus time were derived from the analyzer responses of individual transients. In tobacco (C3), subtraction of the time course of cumulative CO2 exchange under photorespiratory conditions (21 or 43% O2) from that obtained under nonphotorespiratory conditions (1% O2) revealed the presence of an O2-dependent and CO2-reversible component within the first 60 seconds following darkening. This component was absent in maize (C4) and at low external O2:CO2 ratios (i.e. <100) in tobacco. The size of the component in tobacco increased with net photosynthesis as irradiance was increased and was positively associated with inhibition of net photosynthesis by O2. This relatively simple and rapid method of analysis of the transient is introduced to eliminate some uncertainties associated with estimation of photorespiration based on the maximal rate of postillumination CO2 evolution. This method also provides a useful and complementary tool for detecting variation in photorespiration.  相似文献   

20.
Under CO2-limited conditions such as during stomatal closure, photorespiration is suggested to act as a sink for excess light energy and protect photosystem I (PSI) by oxidizing its reaction center chlorophyll P700. In this study, this issue was directly examined with rice (Oryza sativa L.) plants via genetic manipulation of the amount of Rubisco, which can be a limiting factor for photorespiration. At low [CO2] of 5 Pa that mimicked stomatal closure condition, the activity of photorespiration in transgenic plants with decreased Rubisco content (RBCS-antisense plants) markedly decreased, whereas the activity in transgenic plants with overproduction of Rubisco (RBCS-sense plants) was similar to that in wild-type plants. Oxidation of P700 was enhanced at [CO2] of 5 Pa in wild-type and RBCS-sense plants. PSI was not damaged by excess light stress induced by repetitive saturated pulse-light (rSP) in the presence of strong steady-state light. On the other hand, P700 was strongly reduced in RBCS-antisense plants at [CO2] of 5 Pa. PSI was also damaged by rSP illumination. These results indicate that oxidation of P700 and the robustness of PSI against excess light stress are hampered by the decreased activity of photorespiration as a result of genetic manipulation of Rubisco content. It is also suggested that overproduction of Rubisco does not enhance photorespiration as well as CO2 assimilation probably due to partial deactivation of Rubisco.  相似文献   

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