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1.
Compared with C 3 plants, C 4 plants possess a mechanism to concentrate CO 2 around the ribulose-1,5-bisphosphate carboxylase/oxygenase in chloroplasts of bundle sheath cells so that the carboxylation reaction work at a much more efficient rate, thereby substantially eliminate the oxygenation reaction and the resulting photorespiration. It is observed that C 4 photosynthesis is more efficient than C 3 photosynthesis under conditions of low atmospheric CO 2, heat, drought and salinity, suggesting that these factors are the important drivers to promote C 4 evolution. Although C 4 evolution took over 66 times independently, it is hypothesized that it shared the following evolutionary trajectory: 1) gene duplication followed by neofunctionalization; 2) anatomical and ultrastructral changes of leaf architecture to improve the hydraulic systems; 3) establishment of two-celled photorespiratory pump; 4) addition of transport system; 5) co-option of the duplicated genes into C 4 pathway and adaptive changes of C 4 enzymes. Based on our current understanding on C 4 evolution, several strategies for engineering C 4 rice have been proposed to increase both photosynthetic efficiency and yield significantly in order to avoid international food crisis in the future, especially in the developing countries. Here we summarize the latest progresses on the studies of C 4 evolution and discuss the strategies to introduce two-celled C 4 pathway into rice. 相似文献
2.
Engineering C 4 photosynthesis into rice has been considered a promising strategy to increase photosynthesis and yield. A question that remains to be answered is whether expressing a C 4 metabolic cycle into a C 3 leaf structure and without removing the C 3 background metabolism improves photosynthetic efficiency. To explore this question, we developed a 3D reaction diffusion model of bundle‐sheath and connected mesophyll cells in a C 3 rice leaf. Our results show that integrating a C 4 metabolic pathway into rice leaves with a C 3 metabolism and mesophyll structure may lead to an improved photosynthesis under current ambient CO 2 concentration. We analysed a number of physiological factors that influence the CO 2 uptake rate, which include the chloroplast surface area exposed to intercellular air space, bundle‐sheath cell wall thickness, bundle‐sheath chloroplast envelope permeability, Rubisco concentration and the energy partitioning between C 3 and C 4 cycles. Among these, partitioning of energy between C 3 and C 4 photosynthesis and the partitioning of Rubisco between mesophyll and bundle‐sheath cells are decisive factors controlling photosynthetic efficiency in an engineered C 3–C 4 leaf. The implications of the results for the sequence of C 4 evolution are also discussed. 相似文献
3.
C 3 photosynthesis is an inefficient process, because the enzyme that lies at the heart of the Benson–Calvin cycle, ribulose 1,5-bisphosphate carboxylase-oxygenase (Rubisco) is itself a very inefficient enzyme. The oxygenase activity of Rubisco is an unavoidable side reaction that is a consequence of its reaction mechanism. The product of oxygenation, glycollate 2-P, has to be retrieved by photorespiration, a process which results in the loss of a quarter of the carbon that was originally present in glycollate 2-P. Photorespiration therefore reduces carbon gain. Purely in terms of carbon economy, there is, therefore, a strong selection pressure on plants to reduce the rate of photorespiration so as to increase carbon gain, but it also improves water- and nitrogen-use efficiency. Possibilities for the manipulation of plants to decrease the amount of photorespiration include the introduction of improved Rubisco from other species, reconfiguring photorespiration, or introducing carbon-concentrating mechanisms, such as inorganic carbon transporters, carboxysomes or pyrenoids, or engineering a full C 4 Kranz pathway using the existing evolutionary progression in C 3–C 4 intermediates as a blueprint. Possible routes and progress to suppressing photorespiration by introducing C 4 photosynthesis in C 3 crop plants will be discussed, including whether single cell C 4 photosynthesis is feasible, how the evolution of C 3–C 4 intermediates can be used as a blueprint for engineering C 4 photosynthesis, which pathway for the C 4 cycle might be introduced and the extent to which processes and structures in C 3 plant might require optimisation. 相似文献
4.
The source of glycolate in photorespiration and its control, a particularly active and controversial research topic in the
1970s, was resolved in large part by several discoveries and observations described here. George Bowes discovered that the
key carboxylation enzyme Rubisco (ribulosebisphosphate carboxylase/oxygenase) is competitively inhibited by O 2 and that O 2 substitutes for CO 2 in the initial `dark' reaction of photosynthesis to yield glycolate-P, the substrate for photorespiration. William Laing
derived an equation from basic enzyme kinetics that describes the CO 2, O 2, and temperature dependence of photosynthesis, photorespiration, and the CO 2 compensation point in C 3 plants. Jerome Servaites established that photosynthesis cannot be increased by inhibiting the photorespiratory pathway prior
to the release of photorespiratory CO 2, and Douglas Jordan discovered substantial natural variation in the Rubisco oxygenase/carboxylase ratio. A mutant Arabidopsis plant with defective glycolate-P phosphatase, isolated by Chris Somerville, definitively established the role of O 2 and Rubisco in providing photorespiratory glycolate. Selection techniques to isolate photorespiration-deficient plants were
devised by Jack Widholm and by Somerville, but no plants with reduced photorespiration were found. Somerville's approach,
directed mutagenesis of Arabidopsis plants, was subsequently successful in the isolation of numerous other classes of mutants and revolutionized the science
of plant biology.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
5.
Photorespiratory metabolism is essential for plants to maintain functional photosynthesis in an oxygen‐containing environment. Because the oxygenation reaction of Rubisco is followed by the loss of previously fixed carbon, photorespiration is often considered a wasteful process and considerable efforts are aimed at minimizing the negative impact of photorespiration on the plant’s carbon uptake. However, the photorespiratory pathway has also many positive aspects, as it is well integrated within other metabolic processes, such as nitrogen assimilation and C 1 metabolism, and it is important for maintaining the redox balance of the plant. The overall effect of photorespiratory carbon loss on the net CO 2 fixation of the plant is also strongly influenced by the physiology of the leaf related to CO 2 diffusion. This review outlines the distinction between Rubisco oxygenation and photorespiratory CO 2 release as a basis to evaluate the costs and benefits of photorespiration. 相似文献
6.
Phosphoenolpyruvate carboxylase (PEPC) catalyzes the initial fixation of CO 2 in C 4 plants. Under the control of the rice Rubisco small subunit promoter, cDNA of a C 4 SiPPC gene cloned from Seteria italica was introduced into Japonica rice by Agrobacterium-mediated transformation. Integration of the gene was confirmed by PCR analysis. RT-PCR showed expression of the gene at the RNA level in transgenic plants, and enzyme activity measurements confirmed the increase in PEPC protein. The transformants showed improvements in both photosynthesis rate and yield only under upland field cultivation. The possible function of PEPC in rice stress tolerance is discussed. 相似文献
8.
Photosynthesis is the basis of plant growth, and improving photosynthesis can contribute toward greater food security in the coming decades as world population increases. Multiple targets have been identified that could be manipulated to increase crop photosynthesis. The most important target is Rubisco because it catalyses both carboxylation and oxygenation reactions and the majority of responses of photosynthesis to light, CO 2, and temperature are reflected in its kinetic properties. Oxygenase activity can be reduced either by concentrating CO 2 around Rubisco or by modifying the kinetic properties of Rubisco. The C 4 photosynthetic pathway is a CO 2-concentrating mechanism that generally enables C 4 plants to achieve greater efficiency in their use of light, nitrogen, and water than C 3 plants. To capitalize on these advantages, attempts have been made to engineer the C 4 pathway into C 3 rice ( Oryza sativa). A simpler approach is to transfer bicarbonate transporters from cyanobacteria into chloroplasts and prevent CO 2 leakage. Recent technological breakthroughs now allow higher plant Rubisco to be engineered and assembled successfully in planta. Novel amino acid sequences can be introduced that have been impossible to reach via normal evolution, potentially enlarging the range of kinetic properties and breaking free from the constraints associated with covariation that have been observed between certain kinetic parameters. Capturing the promise of improved photosynthesis in greater yield potential will require continued efforts to improve carbon allocation within the plant as well as to maintain grain quality and resistance to disease and lodging.Photosynthesis is the process plants use to capture energy from sunlight and convert it into biochemical energy, which is subsequently used to support nearly all life on Earth. Plant growth depends on photosynthesis, but it is simplistic to think that growth rate directly reflects photosynthetic rate. Continued growth requires the acquisition of water and nutrients in addition to light and CO 2 and, in many cases, involves competition with neighboring plants. Biomass must be invested by the plant to acquire these resources, and respiration is necessary to maintain all the living cells in a plant. Photosynthetic rate is typically measured by enclosing part of a leaf in a chamber, but to understand growth, one needs to consider the daily integral of photosynthetic uptake by the whole plant or community and how it is allocated. Almost inevitably, changing photosynthesis in some way requires more resources. Consequently, in order to improve photosynthesis, one needs to consider the tradeoffs elsewhere in the system. The title, “Improving Photosynthesis,” could be interpreted in many ways. For this review, I am restricting the scope to focus on crop species growing under favorable conditions.To support the forecast growth in human population, large increases in crop yields will be required ( Reynolds et al., 2011; Ziska et al., 2012). Dramatic increases in yield were achieved by the Green Revolution through the introduction of dwarfing genes into the most important C 3 cereal crops rice ( Oryza sativa) and wheat ( Triticum aestivum). This allowed greater use of fertilizer, particularly nitrogen, without the risk of lodging, where the canopy collapses under the weight of the grain, causing significant yield losses ( Stapper and Fischer, 1990). It also meant that biomass allocation within the plant could be altered to increase grain mass at the expense of stem mass now that the plants were shorter. Retrospective comparisons of cultivars released over time, but grown concurrently under favorable conditions with weed, pest, and disease control and physical support to prevent lodging, reveal that while modern cultivars yield more grain, they have similar total aboveground biomass ( Austin et al., 1980, 1989).It is interesting to revisit the review by Gifford and Evans (1981): “over the course of evolution from the wild plant to modern cultivar, carbon partitioning was improved. Thus, as remaining scope for further improvement in carbon allocation must be small, it would be better to aim at increasing photosynthetic and growth rates. Alternatively, as partitioning is where flexibility has been manipulated in the past, it is better to aim for further increases in harvest index.” Just over 30 years have passed since this was published, and yield gains made by plant breeders have continued to come largely from increasing carbon allocation into grain ( Fischer and Edmeades, 2010) and selecting for increased early vigor ( Richards et al., 2010). By contrast, selection based on improving photosynthesis has yet to be achieved. Plants need leaves and roots to capture light, water, and nutrients for growth and stems to form the leaf canopy and support the flowers and grain, so further increases in harvest index may lead to a decrease in yield. Therefore, in order to increase yield potential further, it is necessary to increase total biomass. If light interception through the growing season is already fully exploited, then increasing biomass requires that photosynthesis be increased. It is the realization that further significant increases in yield potential will not be possible by continuing the current strategy that has turned attention toward improving photosynthesis. Recent technological developments now provide us with the means to engineer changes to photosynthesis that would not have been possible previously. 相似文献
9.
Restrictions to photosynthesis can limit plant growth at high temperature in a variety of ways. In addition to increasing photorespiration, moderately high temperatures (35–42 °C) can cause direct injury to the photosynthetic apparatus. Both carbon metabolism and thylakoid reactions have been suggested as the primary site of injury at these temperatures. In the present study this issue was addressed by first characterizing leaf temperature dynamics in Pima cotton ( Gossypium barbadense) grown under irrigation in the US desert south‐west. It was found that cotton leaves repeatedly reached temperatures above 40 °C and could fluctuate as much as 8 or 10 °C in a matter of seconds. Laboratory studies revealed a maximum photosynthetic rate at 30–33 °C that declined by 22% at 45 °C. The majority of the inhibition persisted upon return to 30 °C. The mechanism of this limitation was assessed by measuring the response of photosynthesis to CO 2 in the laboratory. The first time a cotton leaf (grown at 30 °C) was exposed to 45 °C, photosynthetic electron transport was stimulated (at high CO 2) because of an increased flux through the photorespiratory pathway. However, upon cooling back to 30 °C, photosynthetic electron transport was inhibited and fell substantially below the level measured before the heat treatment. In the field, the response of assimilation ( A) to various internal levels of CO 2 ( Ci) revealed that photosynthesis was limited by ribulose‐1,5‐bisphosphate (RuBP) regeneration at normal levels of CO 2 (presumably because of limitations in thylakoid reactions needed to support RuBP regeneration). There was no evidence of a ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) limitation at air levels of CO 2 and at no point on any of 30 A– Ci curves measured on leaves at temperatures from 28 to 39 °C was RuBP regeneration capacity measured to be in substantial excess of the capacity of Rubisco to use RuBP. It is therefore concluded that photosynthesis in field‐grown Pima cotton leaves is functionally limited by photosynthetic electron transport and RuBP regeneration capacity, not Rubisco activity. 相似文献
10.
Metabolome analyses have indicated an accumulation of sedoheptulose 7-phosphate in transgenic rice plants with overproduction of Rubisco (Suzuki et al. in Plant Cell Environ 35:1369–1379, 2012. doi: 10.1111/j.1365-3040.2012.02494.x). Since Rubisco overproduction did not quantitatively enhance photosynthesis even under CO 2-limited conditions, it is suspected that such an accumulation of sedoheptulose 7-phosphate hampers the improvement of photosynthetic capacity. In the present study, the gene of transketolase, which is involved in the metabolism of sedoheptulose 7-phosphate, was co-overexpressed with the Rubisco small subunit gene in rice. Rubisco and transketolase were successfully overproduced in comparison with those in wild-type plants by 35–53 and 39–84 %, respectively. These changes in the amounts of the proteins were associated with those of the mRNA levels. However, the rate of CO 2 assimilation under high irradiance and different [CO 2] did not differ between co-overexpressed plants and wild-type plants. Thus, co-overproduction of Rubisco and transketolase did not improve photosynthesis in rice. Transketolase was probably not a limiting factor of photosynthesis as overproduction of transketolase alone by 80–94 % did not affect photosynthesis. 相似文献
11.
The combined effects of O 2 on net rates of photosynthesis, photosystem II activity, steady‐state pool size of key metabolites of photosynthetic metabolism in the C 4 pathway, C 3 pathway and C 2 photorespiratory cycle and on growth were evaluated in the C 4 species Amaranthus edulis and the C 3 species Flaveria pringlei. Increasing O 2 reduced net CO 2 assimilation in F. pringlei due to an increased flux of C through the photorespiratory pathway. However, in A. edulis increasing O 2 up to 5–10% stimulated photosynthesis. Analysis of the pool size of key metabolites in A. edulis suggests that while there is some O 2 dependent photorespiration, O 2 is required for maximizing C 4 cycle activity to concentrate CO 2 in bundle sheath cells. Therefore, the response of net photosynthesis to O 2 in C 4 plants may result from the balance of these two opposing effects. Under 21 versus 5% O 2, growth of A. edulis was stimulated about 30% whereas that of F. pringlei was inhibited about 40%. 相似文献
12.
Most organisms inhabiting earth feed directly or indirectly on the products synthesized by the reaction of photosynthesis,
which at the current atmospheric CO 2 levels operates only at two thirds of its peak efficiency. Restricting the photorespiratory loss of carbon and thereby improving
the efficiency of photosynthesis is seen by many as a good option to enhance productivity of food crops. Research during last
half a century has shown that several plant species developed CO 2-concentrating mechanism (CCM) to restrict photorespiration under lower concentration of available CO 2. CCMs are now known to be operative in several terrestrial and aquatic plants, ranging from most advanced higher plants to
algae, cyanobacteria and diatoms. Plants with C 4 pathway of photosynthesis (where four-carbon compound is the first product of photosynthesis) or crassulacean acid metabolism
(CAM) may consistently operate CCM. Some plants however can undergo a shift in photosynthetic metabolism only with change
in environmental variables. More recently, a shift in plant photosynthetic metabolism is reported at high altitude where improved
efficiency of CO 2 uptake is related to the recapture of photorespiratory loss of carbon. Of the divergent CO 2 assimilation strategies operative in different oraganisms, the capacity to recapture photorespiratory CO 2 could be an important approach to develop plants with efficient photosynthetic capacity. 相似文献
13.
BackgroundRubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase) catalyses the key reaction in the photosynthetic assimilation of CO 2. In C 4 plants CO 2 is supplied to Rubisco by an auxiliary CO 2-concentrating pathway that helps to maximize the carboxylase activity of the enzyme while suppressing its oxygenase activity. As a consequence, C 4 Rubisco exhibits a higher maximum velocity but lower substrate specificity compared with the C 3 enzyme. Specific amino-acids in Rubisco are associated with C 4 photosynthesis in monocots, but it is not known whether selection has acted on Rubisco in a similar way in eudicots. Methodology/Principal FindingsWe investigated Rubisco evolution in Amaranthaceae sensu lato (including Chenopodiaceae), the third-largest family of C 4 plants, using phylogeny-based maximum likelihood and Bayesian methods to detect Darwinian selection on the chloroplast rbcL gene in a sample of 179 species. Two Rubisco residues, 281 and 309, were found to be under positive selection in C 4 Amaranthaceae with multiple parallel replacements of alanine by serine at position 281 and methionine by isoleucine at position 309. Remarkably, both amino-acids have been detected in other C 4 plant groups, such as C 4 monocots, illustrating a striking parallelism in molecular evolution. Conclusions/SignificanceOur findings illustrate how simple genetic changes can contribute to the evolution of photosynthesis and strengthen the hypothesis that parallel amino-acid replacements are associated with adaptive changes in Rubisco. 相似文献
14.
Plants from two Sedobassia sedoides (Pall.) Aschers populations (Makan and Valitovo) (Chenopodiaceae) with C 2 photosynthesis (precursor of C 4 photosynthesis in phylogenesis) and photorespiratory CO 2-concentrating mechanism were studied. Genetic polymorphism and isotope discrimination (δ 13С) levels of the plants were determined under natural conditions, and their morpho-physiological parameters such as fresh and dry biomass of the above ground parts of plants, functioning of photosystem I (PSI) and photosystem II (PSII), intensity of net photosynthesis (A), transpiration (E), photorespiration and water use efficiency (WUE) of plants were calculated under control and salinine conditions (0 and 200 mM NaCl). Results of the population-genetic analysis showed that the Makan population is polymorphic (plastic) and the Valitovo population is monomorphic (narrowly specialized). There were no significant differences between the populations based on δ 13С values or growth parameters, PSII, A, E and WUE under control conditions. Under saline conditions, dry biomass accumulation decreased in the Makan population by 15% and by more than 2- fold in the Valitovo population. Population differences were revealed in terms of photorespiration intensity and P700 oxidation kinetics under control and saline conditions. Under control conditions, Makan plants were characterized by a higher photorespiration intensity, which decreased by 2-fold under saline conditions to the photorespiration level of Valitovo plants. Cyclic electron transport activity was minimal in the control Makan plants, and it increased by almost 2-fold under saline conditions to the level of that in Valitovo plants under control and saline conditions. Under control conditions, photosynthesis in Makan plants can be specified as the proto-Kranz type (transitional type from C 3 to C 2) and that in Valitovo plants can be specified as the C 2 type (C 4 photosynthesis with photorespiratory CO 2-concentrating mechanism), based on their photorespiration level and cyclic electron transport activity. Under saline conditions, Makan plants exhibited features of C 2 photosynthesis. Intraspecific functional differences of photosynthesis were revealed in different populations of intermediate C 3–C 4 plant species S. sedoides which reflect the initial stages of formation of a photorespiratory CO 2-concentrating mechanism during C 4 photosynthesis evolution, accompanied by decrease in salt tolerance. 相似文献
15.
Nitrogen (N) is the basis of plant growth and development and, is considered as one of the priming agents to elevate a range of stresses. Plants use solar radiations through photosynthesis, which amasses the assimilatory components of crop yield to meet the global demand for food. Nitrogen is the main regulator in the allocation of photosynthetic apparatus which changes of the photosynthesis (Pn) and quantum yield (Fv/Fm) of the plant. In the present study, dynamics of the photosynthetic establishment, N-dependent relation with chlorophyll fluorescence attributes and Rubisco efficacy was evaluated in low-N tolerant (cv. CR Dhan 311) and low-N sensitive (cv. Rasi) rice cultivars under low-N and optimum-N conditions. There was a decrease in the stored leaf N under low-N condition, resulting in the decreased Pn and Fv/Fm efficiency of the plants through depletion in the activity and content of Rubisco. The Pn and Fv/Fm followed the parallel trend of leaf N content during low-N condition along with depletion of intercellular CO2 concentration and overall conductance under low-N condition. Photosynthetic saturation curve cleared abrupt decrease of effective quantum yield in the low-N sensitive rice cultivar than the low-N tolerant rice. Also, the rapid light curve highlighted the unacclimated regulation of photochemical and non-photochemical quenching in the low-N condition. The low-N sensitive rice cultivar triumphed non-photochemical quenching, whereas the low-N tolerant rice cultivar rose gradually during the light curve. Our study suggested that the quantum yield is the key limitation for photosynthesis in low-N condition. Regulation of Rubisco, photochemical and non-photochemical quenching may help plants to grow under low-N level. 相似文献
16.
A model of leaf, photosynthesis has been developed for C 3–C 4 intermediate species found in the genera Panicum, Moricandia, Parthenium and Mollugo where no functional C 4 pathway has been identified. Model assumptions are a functional C 3 cycle in both mesophyll and bundle-sheath cells and that glycine formed in the mesophyll, as a consequence of the oxygenase activity of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco, EC 4.1.1.39), diffuses to the bundle sheath, where most of the photorespiratory CO 2 is released. The model describes the observed gas-exchange characteristics of these C 3–C 4 intermediates, such as low CO 2-compensation points () at an O 2 pressure of 200 mbar, a curvilinear response of to changing O 2 pressures, and typical responses of CO 2-assimilation rate to intercellular CO 2 pressure. The model predicts that bundle-sheath CO 2 concentration is highest at low mesophyll CO 2 pressures and decreases as mesophyll CO 2 pressure increases. A partitioning of 5–15% of the total leaf Rubisco into the bundle-sheath cells and a bundlesheath conductance similar to that proposed for C 4 species best mimics the gas-exchange results. The model predicts C 3-like carbon-isotope discrimination for photosynthesis at atmospheric levels of CO 2, but at low CO 2 pressures it predicts a higher discrimination than is typically found during C 3 photosynthesis at lower CO 2 pressures.Abbreviations and symbols PEP
phosphoenolpyruvate
- Rubisco
ribulose-1,5-bisphosphate carboxylase-oxygenase (EC 4.1.1.39)
- RuBP
ribulose-1,5-bisphosphate
-
p(CO 2)
partial pressure of CO 2
-
p(O 2)
partial pressure of O 2. See also p. 471 相似文献
17.
The basis for O 2 sensitivity of C 4 photosynthesis was evaluated using a C 4-cycle-limited mutant of Amaranthus edulis (a phospho enolpyruvate carboxylase-deficient mutant), and a C 3-cycle-limited transformant of Flaveria bidentis (an antisense ribulose-1,5-bisphosphate carboxylase/oxygenase [Rubisco] small subunit transformant). Data obtained with the C 4-cycle-limited mutant showed that atmospheric levels of O 2 (20 kPa) caused increased inhibition of photosynthesis as a result of higher levels of photorespiration. The optimal O 2 partial pressure for photosynthesis was reduced from approximately 5 kPa O 2 to 1 to 2 kPa O 2, becoming similar to that of C 3 plants. Therefore, the higher O 2 requirement for optimal C 4 photosynthesis is specifically associated with the C 4 function. With the Rubisco-limited F. bidentis, there was less inhibition of photosynthesis by supraoptimal levels of O 2 than in the wild type. When CO 2 fixation by Rubisco is limited, an increase in the CO 2 concentration in bundle-sheath cells via the C 4 cycle may further reduce the oxygenase activity of Rubisco and decrease the inhibition of photosynthesis by high partial pressures of O 2 while increasing CO 2 leakage and overcycling of the C 4 pathway. These results indicate that in C 4 plants the investment in the C 3 and C 4 cycles must be balanced for maximum efficiency. 相似文献
18.
The photosynthetic performance of C 4 plants is generally inferior to that of C 3 species at low temperatures, but the reasons for this are unclear. The present study investigated the hypothesis that the capacity of Rubisco, which largely reflects Rubisco content, limits C 4 photosynthesis at suboptimal temperatures. Photosynthetic gas exchange, chlorophyll a fluorescence, and the in vitro activity of Rubisco between 5 and 35 °C were measured to examine the nature of the low‐temperature photosynthetic performance of the co‐occurring high latitude grasses, Muhlenbergia glomerata (C 4) and Calamogrostis canadensis (C 3). Plants were grown under cool (14/10 °C) and warm (26/22 °C) temperature regimes to examine whether acclimation to cool temperature alters patterns of photosynthetic limitation. Low‐temperature acclimation reduced photosynthetic rates in both species. The catalytic site concentration of Rubisco was approximately 5.0 and 20 µmol m ?2 in M. glomerata and C. canadensis, respectively, regardless of growth temperature. In both species, in vivo electron transport rates below the thermal optimum exceeded what was necessary to support photosynthesis. In warm‐grown C. canadensis, the photosynthesis rate below 15 °C was unaffected by a 90% reduction in O 2 content, indicating photosynthetic capacity was limited by the capacity of P i‐regeneration. By contrast, the rate of photosynthesis in C. canadensis plants grown at the cooler temperatures was stimulated 20–30% by O 2 reduction, indicating the P i‐regeneration limitation was removed during low‐temperature acclimation. In M. glomerata, in vitro Rubisco activity and gross CO 2 assimilation rate were equivalent below 25 °C, indicating that the capacity of the enzyme is a major rate limiting step during C 4 photosynthesis at cool temperatures. 相似文献
19.
Partial nitrate nutrition (PNN) was found to improve rice ( Oryza sativa L. var. japonica) growth. However, how PNN is related to photosynthesis in rice cultivars with different nitrogen use efficiency (NUE) is
still not clear. Two rice cultivars, Nanguang (high NUE) and Elio (low NUE), were grown under sole NH 4
+ and PNN at a total nitrogen concentration of 2.86 mM. The dry weight, leaf area, ribulose-1,5-bisphosphate carboxylase/oxygenase
(Rubisco) and gas exchange parameters were measured. Nitrogen and Rubisco contents in the newly expanded leaves of cv. Nanguang
were similar to those of cv. Elio when only NH 4
+ was supplemented in the nutrient solution. However, in cv. Nanguang, nitrogen and Rubisco contents increased under PNN than
under sole NH 4
+ nutrition. Higher nitrogen and Rubisco contents were recorded in cv. Nanguang than in cv. Elio under PNN. The ratio of carboxylation
efficiency (CE) to Rubisco content in cv. Nanguang was 11 and 14% higher than that in cv. Elio under NH 4
+ and PNN, respectively. CE was 14% higher in cv. Nanguang than that in cv. Elio. The results suggest that PNN causes an increase
in photosynthesis in cv. Nanguang. It is concluded that differences in Rubisco activity, rather than stomatal limitation,
are responsible for the differences in photosynthesis between the two cultivars. The presence of nitrate increases Rubisco
content in rice with a high NUE, which leads to faster biomass accumulation at later growth stages. 相似文献
20.
The leafless amphibious sedge Eleocharis vivipara develops culms with C 4 traits and Kranz anatomy under terrestrial conditions, but develops culms with C 3 traits and non-Kranz anatomy under submerged conditions. The culms of the terrestrial form have high C 4 enzyme activities, while those of the submerged form have decreased C 4 enzyme activities. The culms accumulate ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) in the mesophyll cells
(MC) and the bundle sheath cells. The Rubisco in the MC may be responsible for the operation of the C 3 pathway in the submerged form. To verify the presence of the C 3 cycle in the MC, we examined the effects of 3,3-dichloro-2-(dihydroxyphosphinoylmethyl) -propenoate (DCDP), an inhibitor
of phospho enolpyruvate carboxylase (PEPC), on photosynthesis in culms of the terrestrial forms of E. vivipara and related amphibious species, E. baldwinii and E. retroflexa ssp. chaetaria. When 1 mM DCDP was fed via the transpiration stream to excised leaves, photosynthesis was inhibited completely in Fimbristylis dichotoma (C 4 control), but by only 20% in potato (C 3 control). In the terrestrial Eleocharis plants, the degree of inhibition of photosynthesis by DCDP was intermediate between those of the C 4 and C 3 plants, at 58–81%. These results suggest that photosynthesis under DCDP treatment in the terrestrial Eleocharis plants is due mainly to fixation of atmospheric CO 2 by Rubisco and probably the C 3 cycle in the MC. These features are reminiscent of those in C 4-like plants. Differential effects of DCDP on photosynthesis of the 3 Eleocharis species are discussed in relation to differences in the degree of Rubisco accumulation and C 3 activity in the MC.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
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