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1.
Leaves of C 3 plants which exhibit a normal O 2 inhibition of CO 2 fixation at less than saturating light intensity were found to exhibit O 2-insensitive photosynthesis at high light. This behavior was observed in Phaseolus vulgaris L., Xanthium strumarium L., and Scrophularia desertorum (Shaw.) Munz. O 2-insensitive photosynthesis has been reported in nine other C 3 species and usually occurred when the intercellular CO 2 pressure was about double the normal pressure. A lack of O 2 inhibition of photosynthesis was always accompanied by a failure of increased CO 2 pressure to stimulate photosynthesis to the expected degree. O 2-insensitive photosynthesis also occurred after plants had been water stressed. Under such conditions, however, photosynthesis became O 2 and CO 2 insensitive at physiological CO 2 pressures. Postillumination CO 2 exchange kinetics showed that O 2 and CO 2 insensitivity was not the result of elimination of photorespiration. It is proposed that O2 and CO2 insensitivity occurs when the concentration of phosphate in the chloroplast stroma cannot be both high enough to allow photophosphorylation and low enough to allow starch and sucrose synthesis at the rates required by the rest of the photosynthetic component processes. Under these conditions, the energy diverted to photorespiration does not adversely affect the potential for CO2 assimilation. 相似文献
2.
The inhibition of photosynthetic electron transport when starch and sucrose synthesis limit the overall rate of photosynthesis was studied in Phaseolus vulgaris L. and Xanthium strumarium L. The starch and sucrose limitation was established by reducing photorespiration by manipulation of the partial pressure of O 2 and CO 2. Chlorophyll a fluorescence quenching, the redox state of Photosystem I (estimated by the redox status of NADP-dependent malate dehydrogenase), and the intermediates of the xanthophyll cycle were investigated. Non-photochemical fluorescence quenching increased, NADP-dependent malate dehydrogenase remained at 100% activity, and the amount of violaxanthin decreased when starch and sucrose synthesis limited photosynthesis. In addition, O 2-induced feedback caused a decrease in photochemical quenching. These results are consistent with a downward regulation of photosynthetic electron transport during end product feedback on photosynthesis. When leaves were held in high CO 2 for 4 hours, the efficiency of Photosystem II was reduced when subsequently measured under low light. The results indicate that the quantum efficiency of open Photosystem II centers was reduced by the 4 hour treatment. We interpret the results to indicate that feedback from starch and sucrose synthesis on photosynthetic electron transport stimulates mechanisms for dissipating excess light energy but that these mechanisms do not completely protect leaves from long-term inhibition of photosynthetic electron transport capacity. 相似文献
3.
The balance between carbon assimilation, storage and utilisation during photosynthesis is dependent on partitioning of photoassimilate between starch and sucrose, and varies in response to changes in the environment. However, the extent to which the capacity to modulate carbon partitioning rapidly through short‐term allosteric regulation may contribute to plant performance is unknown. Here we examine the physiological role of fructose 2,6‐bisphosphate (Fru‐2,6‐P 2) during photosynthesis, growth and reproduction in Arabidopsis thaliana (L.). In leaves this signal metabolite contributes to coordination of carbon assimilation and partitioning during photosynthesis by allosterically modulating the activity of cytosolic fructose‐1,6‐bisphosphatase. Three independent T‐DNA insertional mutant lines deficient in 6‐phosphofructo‐2‐kinase/fructose‐2,6‐bisphosphatase (F2KP), the bifunctional enzyme responsible for both the synthesis and degradation of Fru‐2,6‐P 2, lack Fru‐2,6‐P 2. These plants have normal steady‐state rates of photosynthesis, but exhibit increased partitioning of photoassimilate into sucrose and have delayed photosynthetic induction kinetics. The F2KP‐deficient plants grow normally in constant environments, but show reduced growth and seed yields relative to wildtype plants in fluctuating light and/or temperature. We conclude that Fru‐2,6‐P 2 is required for optimum regulation of photosynthetic carbon metabolism under variable growth conditions. These analyses suggest that the capacity of Fru‐2,6‐P 2 to modulate partitioning of photoassimilate is an important determinant of growth and fitness in natural environments. 相似文献
4.
Improvements in plant productivity (biomass) and yield have centered on increasing the efficiency of leaf CO 2 fixation and utilization of products by non-photosynthetic sink organs. We had previously demonstrated a correlation between photosynthetic capacity, plant growth, and the extent of leaf starch synthesis utilizing starch-deficient mutants. This finding suggested that leaf starch is used as a transient photosynthetic sink to recycle inorganic phosphate and, in turn, maximize photosynthesis. To test this hypothesis, Arabidopsis thaliana and rice ( Oryza sativa L.) lines were generated with enhanced capacity to make leaf starch with minimal impact on carbon partitioning to sucrose. The Arabidopsis engineered plants exhibited enhanced photosynthetic capacity; this translated into increased growth and biomass. These enhanced phenotypes were displayed by similarly engineered rice lines. Manipulation of leaf starch is a viable alternative strategy to increase photosynthesis and, in turn, the growth and yields of crop and bioenergy plants. 相似文献
5.
The ability of 21 C 3 and C 4 monocot and dicot species to rapidly export newly fixed C in the light at both ambient and enriched CO 2 levels was compared. Photosynthesis and concurrent export rates were estimated during isotopic equilibrium of the transport sugars using a steady-state 14CO 2-labeling procedure. At ambient CO 2 photosynthesis and export rates for C 3 species were 5 to 15 and 1 to 10 μmol C m −2 s −1, respectively, and 20 to 30 and 15 to 22 μmol C m −2 s −1, respectively, for C 4 species. A linear regression plot of export on photosynthesis rate of all species had a correlation coefficient of 0.87. When concurrent export was expressed as a percentage of photosynthesis, several C 3 dicots that produced transport sugars other than Suc had high efflux rates relative to photosynthesis, comparable to those of C 4 species. At high CO 2 photosynthetic and export rates were only slightly altered in C 4 species, and photosynthesis increased but export rates did not in all C 3 species. The C 3 species that had high efflux rates relative to photosynthesis at ambient CO 2 exported at rates comparable to those of C 4 species on both an absolute basis and as a percentage of photosynthesis. At ambient CO 2 there were strong linear relationships between photosynthesis, sugar synthesis, and concurrent export. However, at high CO 2 the relationships between photosynthesis and export rate and between sugar synthesis and export rate were not as strong because sugars and starch were accumulated. 相似文献
6.
Flaveria bidentis (L.) Kuntze, a C 4 dicot, was genetically transformed with a construct encoding the mature form of tobacco ( Nicotiana tabacum L.) carbonic anhydrase (CA) under the control of a strong constitutive promoter. Expression of the tobacco CA was detected in transformant whole-leaf and bundle-sheath cell (bsc) extracts by immunoblot analysis. Whole-leaf extracts from two CA-transformed lines demonstrated 10% to 50% more CA activity on a ribulose-1,5-bisphosphate carboxylase/oxygenase-site basis than the extracts from transformed, nonexpressing control plants, whereas 3 to 5 times more activity was measured in CA transformant bsc extracts. This increased CA activity resulted in plants with moderately reduced rates of CO 2 assimilation (A) and an appreciable increase in C isotope discrimination compared with the controls. With increasing O 2 concentrations up to 40% (v/v), a greater inhibition of A was found for transformants than for wild-type plants; however, the quantum yield of photosystem II did not differ appreciably between these two groups over the O 2 levels tested. The quantum yield of photosystem II-to-A ratio suggested that at higher O 2 concentrations, the transformants had increased rates of photorespiration. Thus, the expression of active tobacco CA in the cytosol of F. bidentis bsc and mesophyll cells perturbed the C 4 CO 2-concentrating mechanism by increasing the permeability of the bsc to inorganic C and, thereby, decreasing the availability of CO 2 for photosynthetic assimilation by ribulose-1,5-bisphosphate carboxylase/oxygenase. 相似文献
7.
Tobacco ( Nicotiana tabacum) mutants with 40 to 50% more catalase activity than wild type show O 2-resistant photosynthesis under conditions of high photorespiration. More than 90% of the population of mutant plants of an M 7 and M 8 generation had enhanced catalase activity, and nearly 40% had activities >3 standard deviations above the mean of wild type. Superoxide dismutase activity was the same in mutant and wild-type leaves. The greater photosynthetic rate of mutant leaves previously observed in the laboratory was confirmed with field-grown plants that showed significantly higher rates (8%) than wild type during 8 days of measurements during a 19-day period of active growth. The tip region of expanding mutant leaves had higher catalase activity than the base of the lamina, and photosynthesis was O 2 resistant in 42% O 2 in the tip compared with the base, thus further supporting the hypothesis that there is a biochemical linkage between these traits. Plants grown in high light (270 micromole photons per square meter per second) had greater catalase activity and an activity ratio of mutant to wild type of 1.45 compared with 1.22 for those grown in low light (130 micromole photons per square meter per second). After acclimation for 3 weeks, plants transferred from low to high light showed increasing activities, and after 5 days the activity ratio of mutant to wild type was the same as in plants acclimated in higher light. The role of enhanced catalase activity in reducing photorespiratory CO 2 is discussed. 相似文献
8.
We have investigated the role of polyunsaturated fatty acids in photosynthesis using a triple mutant of Arabidopsis thaliana that lacks trienoic fatty acids ( fad 3-2 fad 7-2 fad 8). Though this mutant is male sterile, vegetative growth and development under normal conditions are largely unaffected (McConn
and Browse, 1996 Plant Cell 8: 403–416). At 0.2–1.0 kPa vapor pressure deficit (low VPD), maximum photosynthetic rates of
wild-type and mutant plants were similar while stomatal conductance rates were up to 2 times higher in mutant plants. However,
light-saturated rates of carbon assimilation and stomatal conductance in the mutant were lower than in wild-type plants when
measured at ambient (35 Pa) CO 2 and 2.0–2.8 kPa vapor pressure deficit (high VPD). The limitation to photosynthesis in the mutant plants at high VPD was
overcome by saturating partial pressures of CO 2 suggesting a stomatal limitation. Chlorophyll fluorescence measurements indicate that differences observed in maximum assimilation
rates were not due to limitations within the photochemical reactions of photosynthesis. Stomatal response to VPD and intrinsic
water use efficiency was drastically different in mutant versus wild-type plants. The results of this investigation indicate
that for Arabidopsis, polyunsaturated fatty acids may be an important determinant of responses of photosynthesis and stomatal conductance to environmental
stresses such as high VPD.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
10.
The regulation of ribulose-1,5-bisphosphate (RuBP) carboxylase (rubisco) activity in Phaseolus vulgaris was studied under moderate CO 2 and high light, conditions in which photosynthesis in C 3 plants can be insensitive to changes in O 2 partial pressure. Steady state RuBP concentrations were higher, the calculated rate of RuBP use was lower and the activation state of rubisco was lower in low O 2 relative to values observed in normal O 2. It is suggested that the reduced activity of rubisco observed here is related to feedback effects which occur when the rate of net CO 2 assimilation approaches the maximum capacity for starch and sucrose synthesis (triose phosphate utilization). The activation state of rubisco was independent of O 2 partial pressure when light or CO 2 was limiting for photosynthesis. Reduced activity of rubisco was also observed at limiting light. However, in this species light dependent changes in the concentration of an inhibitor of rubisco controlled the apparent Vmax of rubisco in low light while changes in the CO 2-Mg 2+ dependent activation of rubisco controlled the apparent Vmax in high light. 相似文献
11.
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
12.
We investigated several photosynthetic parameters of a virescent mutant of durum wheat and of its wild-type. Electron transport rate to ferricyanide was the same in the two genotypes when expressed on leaf area basis while O 2 evolution of the leaf tissue in saturating light and CO 2 was slightly higher in the yellow genotype. RuBPCase was also slightly higher. Quantum yield per absorbed light was similar in the two genotypes. P700 and Cyt f were less concentrated in the mutant while PS II was only marginally lower. The light response curve of CO 2 assimilation indicated higher level of photosynthesis of the mutant in high light, which corresponded to a lower non-photochemical quenching compared to the wild-type. It is concluded that the reaction centres, cyt f and chlorophyll are not limiting factors of electron transport in wheat seedlings and that electron transport capacity is in excess with respect to that needed for driving photosynthesis. Since the differences in photosynthesis reflect differences in RuBPCase activity, it is suggested that this enzyme limits photosynthesis in wheat seedlings also at high light intensities.Abbreviations cyt f
cytochrome f
- chl
chlorophyll
- PS II
photosystem II
- Pn max
maximum photosynthesis
- RuBCase
Ribulose, 1-5,bisphosphate carboxylase 相似文献
13.
A few species of Cymbopogon and Vetiveria are potentially important tropical grasses producing essential oils. In the present study, we report on the leaf anatomy and photosynthetic carbon assimilation in five species of Cymbopogon and Vetiveria zizanioides. Kranz-type leaf anatomy with a centrifugal distribution of chloroplasts and exclusive localization of starch in the bundle sheath cells were common among the test plants. Besides the Kranz leaf anatomy, these grasses displayed other typical C 4 characteristics including a low (0–5 µl/l) CO 2 compensation point, lack of light saturation of CO 2 uptake at high photon flux densities, high temperature (35°C) optimum of net photosynthesis, high rates of net photosynthesis (55–67 mg CO 2 dm -2 leaf area h -1), little or no response of net photosynthesis to atmospheric levels of O 2 and high leaf 13C/ 12C ratios. The biochemical studies with 14CO 2 indicated that the leaves of the above plant species synthesize predominantly malate during short term (5 s) photosynthesis. In pulse-chase experiments it was shown that the synthesis of 3-phosphoglycerate proceeds at the expense of malate, the major first formed product of photosynthesis in these plant species. 相似文献
14.
- Stomata modulate the exchange of water and CO2 between plant and atmosphere. Although stomatal density is known to affect CO2 diffusion into the leaf and thus photosynthetic rate, the effect of stomatal density and patterning on CO2 assimilation is not fully understood.
- We used wild types Col‐0 and C24 and stomatal mutants sdd1‐1 and tmm1 of Arabidopsis thaliana, differing in stomatal density and pattern, to study the effects of these variations on both stomatal and mesophyll conductance and CO2 assimilation rate. Anatomical parameters of stomata, leaf temperature and carbon isotope discrimination were also assessed.
- Our results indicate that increased stomatal density enhanced stomatal conductance in sdd1‐1 plants, with no effect on photosynthesis, due to both unchanged photosynthetic capacity and decreased mesophyll conductance. Clustering (abnormal patterning formed by clusters of two or more stomata) and a highly unequal distribution of stomata between the adaxial and abaxial leaf sides in tmm1 mutants also had no effect on photosynthesis.
- Except at very high stomatal densities, stomatal conductance and water loss were proportional to stomatal density. Stomatal formation in clusters reduced stomatal dynamics and their operational range as well as the efficiency of CO2 transport.
相似文献
15.
Pea chlorophyll mutants chlorotica 2004 and 2014 have been studied. The mutants differ from the initial form (pea cultivar Torsdag) in stem and leaf color (light green in the mutant 2004 and yellow-green in the mutant 2014), relative chlorophyll content (approximately 80 and 50%, respectively), and the composition of carotenoids: the mutant 2004 contains a significantly smaller amount of carotene but accumulates more lutein and violaxanthin; in the mutant 2014, the contents of all carotenoids are decreased proportionally to the decrease in chlorophyll content. It is shown that the rates of CO 2 assimilation and oxygen production by mutant chlorotica 2004 and 2014 plants are reduced. The quantum efficiency of photosynthesis in the mutants is 29–30% lower than in the control plants; in their hybrids, however, it is 1.5–2 times higher. It is proposed that both the greater role of dark respiration in gas exchange and the reduced photosynthetic activity in chlorotica mutants are responsible for the decreased phytomass increment in these plants. On the basis of these results, the conclusion is drawn that mutations chlorotica 2004 and 2014 affect the genes controlling the formation and functioning of various components of the photosynthetic apparatus. 相似文献
16.
The photosynthetic properties of a yellow lethal mutant, Oy/oy, and two yellow-green mutants of maize which are allelic (a homozygous recessive oy/oy and a heterozygous dominant Oy/+) were examined. Although Oy/oy had little or no chlorophyll or capacity for CO 2 fixation compared to normal siblings, it had 28% as much ribulose-1,5-bisphosphate carboxylase oxygenase (Rubisco) activity, and from 40% to near normal activities of C 4 cycle enzymes.Both yellow-green mutants had only half as much chlorophyll per leaf area as normal green seedlings in greenhouse-grown plants in winter and spring. However, the absorbance of light by the mutants was relatively high, as their transmittance was only 5 to 8% greater than normal leaves. In winter-grown greenhouse plants, the activities of Rubisco and several C 4 cycle enzymes in the mutants were unaffected and similar to those of normal seedlings on a leaf area basis. After allowing for small differences in leaf absorbance, the light response curves for photosynthesis in the mutants were similar on a leaf area basis but much higher on a chlorophyll basis than those of the normal seedlings. In spring-grown greenhouse plants the enzyme activities and photosynthesis rates were about 30% lower per leaf area in the yellow-green mutant leaves compared to the wild type. The maximum carboxylation efficiency (measured under low CO 2 and 1000 mol quanta m -2 s -1) in the mutants and normal leaves was similar on a Rubisco protein basis. The results indicate that maize can undergo a 50% reduction in chlorophyll content without a corresponding reduction in enzymes of carbon assimilation, and still maintain a high capacity for photosynthesis.Abbreviations Chl
chlorophyll
- PEP
phosphoenolypruvate
- Rubisco
ribulose-1,5-bisphosphate carboxylase oxygenase
This research was supported by CSIRO and by USDA Competitive Grant 86-CRCR-1-2036. 相似文献
17.
Cotton ( Gossypium hirsutum L. cv Stoneville 213) was grown at 350 and 1000 microliters per liter CO 2. The plants grown at elevated CO 2 concentrations contained large starch pools and showed initial symptoms of visible physical damage. Photosynthetic rates were lower than expected based on instantaneous exposure to high CO 2. A group of plants grown at 1000 microliters per liter CO2 was switched to 350 microliters per liter CO2. Starch pools and photosynthetic rates were monitored in the switched plants and in the two unswitched control groups. Photosynthetic rates per unit leaf area recovered to the level of the 350 microliters per liter CO2 grown control group within four to five days. To assess only nonstomatal limitations to photosynthesis, a measure of photosynthetic efficiencies was calculated (moles CO2 fixed per square meter per second per mole intercellular CO2). Photosynthetic efficiency also recovered to the levels of the 350 microliters per liter CO2 grown controls within three to four days. Recovery was correlated to a rapid depletion of the starch pool, indicating that the inhibition of photosynthesis is primarily a result of feedback inhibition. However, complete recovery may involve the repair of damage to the chloroplasts caused by excessive starch accumulation. The rapid and complete reversal of photosynthetic inhibition suggests that the appearance of large, strong sinks at certain developmental stages could result in reduction of the large starch accumulations and that photosynthetic rates could recover to near the theoretical capacity during periods of high photosynthate demand. 相似文献
18.
In the shade plant Alocasia macrorrhiza grown in low light, photosynthetic CO 2 assimilation during a 5 second lightfleck plus postillumination CO 2 assimilation can allow up to 60% more photosynthesis than that which occurs during 5 seconds of steady state light of the same intensity (RL Chazdon, RW Pearcy 1986 Oecologia. 69: 524-531). Metabolites of photosynthesis were measured to determine if the pool of ribulose 1,5-bisphosphate (RuBP) could account for all of the postillumination CO 2 assimilation following a lightfleck in Alocasia. It was found that the pool of triose-P was much larger than that of RuBP and could account for five times more postillumination CO 2 assimilation than could RuBP. The same trend was seen in the sun plant Phaseolus vulgaris when it was grown in the shade. In contrast, sun-grown Alocasia and Phasiolus did not have a large pool of triose-P relative to RuBP following a lightfleck. In sun plants, carbon may rapidly be converted to RuBP in the light whereas in shade plants there may be a restriction in the path between the triose-P and RuBP pools. It is hypothesized that in shade plants the buildup of triose-P rather than RuBP during the lightfleck prevents inhibition of electron transport which may otherwise occur because of competition for ATP between the two kinases of the photosynthetic carbon reduction cycle. Utilization of the triose-P for postillumination CO 2 fixation would require the capacity for significant postillumination ATP synthesis. The extensive grana stacking and large intrathylakoid space which accompanies the high level of chlorophyll in low-light-grown Alocasia could be an important contributing factor to postillumination ATP formation. 相似文献
19.
Sorghum is one of the most important crops providing food and feed in many of the world's harsher environments. Sorghum utilizes the C 4 pathway of photosynthesis in which a biochemical carbon-concentrating mechanism results in high CO 2 assimilation rates. Overexpressing the Rieske FeS subunit of the Cytochrome b6f complex was previously shown to increase the rate of photosynthetic electron transport and stimulate CO 2 assimilation in the model C 4 plant Setaria viridis. To test whether productivity of C 4 crops could be improved by Rieske overexpression, we created transgenic Sorghum bicolor Tx430 plants with increased Rieske content. The transgenic plants showed no marked changes in abundances of other photosynthetic proteins or chlorophyll content. The steady-state rates of electron transport and CO 2 assimilation did not differ between the plants with increased Rieske abundance and control plants, suggesting that Cytochrome b6f is not the only factor limiting electron transport in sorghum at high light and high CO 2. However, faster responses of non-photochemical quenching as well as an elevated quantum yield of Photosystem II and an increased CO 2 assimilation rate were observed from the plants overexpressing Rieske during the photosynthetic induction, a process of activation of photosynthesis upon the dark–light transition. As a consequence, sorghum with increased Rieske content produced more biomass and grain when grown in glasshouse conditions. Our results indicate that increasing Rieske content has potential to boost productivity of sorghum and other C 4 crops by improving the efficiency of light utilization and conversion to biomass through the faster induction of photosynthesis. 相似文献
20.
Regulation of light harvesting in response to changes in light intensity, CO 2 and O 2 concentration was studied in C 4 species representing three different metabolic subtypes: Sorghum bicolor (NADP-malic enzyme), Amaranthus edulis (NAD-malic enzyme), and Panicum texanum (PEP-carboxykinase). Several photosynthetic parameters were measured on the intact leaf level including CO 2 assimilation rates, O 2 evolution, photosystem II activities, thylakoid proton circuit and dissipation of excitation energy. Gross rates of O 2 evolution (
J\textO2 J_{{{\text{O}}_{2} }} , measured by analysis of chlorophyll fluorescence), net rates of O 2 evolution and CO 2 assimilation responded in parallel to changes in light and CO 2 levels. The C 4 subtypes had similar energy requirements for photosynthesis since there were no significant differences in maximal quantum
efficiencies for gross rates of O 2 evolution (average value = 0.072 O 2/quanta absorbed, ~14 quanta per O 2 evolved). At saturating actinic light intensities, when photosynthesis was suppressed by decreasing CO 2, ATP synthase proton conductivity ( g
H
+) responded strongly to changes in electron flow, decreasing linearly with
J\textO2 J_{{{\text{O}}_{2} }} , which was previously observed in C 3 plants. It is proposed that g
H
+ is controlled at the substrate level by inorganic phosphate availability. The results suggest development of nonphotochemical
quenching in C 4 plants is controlled by a decrease in g
H
+, which causes an increase in proton motive force by restricting proton efflux from the lumen, rather than by cyclic or pseudocyclic
electron flow. 相似文献
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