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1.
The studies described in the paper were conducted with tissue slices of Crassulacean acid metabolism (CAM) plants floating in isotonic buffer. In a first series of experiments, temperature effects on the efflux of [ 14C]malate and 14CO 2 were studied. An increase of temperature increased the efflux from the tissue in a non-linear manner. The efflux was markedly influenced also by the temperatures applied during the pretreatment. The rates of label export in response to the temperature and the relative contributions of 14CO 2 and [ 14C]malate to the label export were different in the two studied CAM plants ( Kalanchoë daigremontiana, Sempervivum montanum). In further experiments, temperature response of the labelling patterns produced by 14CO 2 fixation and light and darkness were studied. In tissue which had accumulated malate (acidified state) an increase of temperature decreased the rates of dark CO 2 fixation whilst the rates of CO 2 fixation in light remained largely unaffected. An increase of temperature shifted the labelling patterns from a C 4-type (malate being the mainly labelled compound) into a C 3-type (label in carbohydrates). No such shift in the labelling patterns could be observed in the tissue which had depleted the previously stored malate (deacidified state). The results indicate that in the acidified tissue the increase of temperature increases the efflux of malate from the vacuole by changing the properties of the tonoplast. It is assumed that the increased export of malic acid lowers the in-vivo activity of phosphoenol pyruvate carboxylase by feedback inhibition.Abbreviations CAM
Crassulacean acid metabolism
- FW
fresh weight
- PEPCase
phosphoenolpyruvate carboxylase
Dedicated to Professor O.L. Lange, Würzburg, on the occasion of his 60th birthday 相似文献
2.
Photosynthesis was examined in leaves of Flaveria brownii A. M. Powell, grown under either 14% or 100% full sunlight. In leaves of high light grown plants, the CO 2 compensation point and the inhibition of photosynthesis by 21% O 2 were significantly lower, while activities of ribulose 1,5-bisphosphate carboxylase/oxygenase and various C 4 cycle enzymes were considerably higher than those in leaves grown in low light. Both the CO 2 compensation point and the degree of O 2 inhibition of apparent photosynthesis were relatively insensitive to the light intensity used during measurements with plants from either growth conditions. Partitioning of atmospheric CO 2 between Rubisco of the C 3 pathway and phosphoenolpyruvate carboxylase of the C 4 cycle was determined by exposing leaves to 14CO 2 for 3 to 16 seconds, and extrapolating the labeling curves of initial products to zero time. Results indicated that ~94% of the CO 2 was fixed by the C 4 cycle in high light grown plants, versus ~78% in low light grown plants. Thus, growth of F. brownii in high light increased the expressed level of C 4 photosynthesis. Consistent with the carbon partitioning patterns, photosynthetic enzyme activities (on a chlorophyll basis) in protoplasts from leaves of high light grown plants showed a more C 4-like pattern of compartmentation. Pyruvate, Pi dikinase and phosphoenolpyruvate carboxylase were more enriched in the mesophyll cells, while NADP-malic enzyme and ribulose 1,5-bisphosphate carboxylase/oxygenase were relatively more abundant in the bundle sheath cells of high light than of low light grown plants. Thus, these results indicate that F. brownii has plasticity in its utilization of different pathways of carbon assimilation, depending on the light conditions during growth. 相似文献
3.
Phosphoenolpyruvate carboxylase is regulated by reversible phosphorylation in response to light in C 3 and C 4 plants and to a circadian oscillator in CAM plants. Increases in phosphoenolpyruvate carboxylase kinase activity require protein synthesis. This requirement has been analysed by quantifying translatable mRNA for this protein kinase using in vitro translation of isolated RNA followed by direct assay of kinase activity. In leaves of the CAM plant Bryophyllum (Kalanchoë) fedtschenkoi, in normal diurnal conditions, kinase mRNA was 20-fold more abundant at night than in the day. In constant environmental conditions (continuous darkness, CO 2-free air, 15°C) kinase mRNA exhibited circadian oscillations. The circadian disappearance of kinase mRNA and kinase activity was delayed by lowering the temperature to 4°C and accelerated by raising the temperature to 30°C. The appearance of kinase mRNA and activity was blocked by cordycepin and puromycin. In maize and barley, kinase mRNA increased in response to light. For all three plants, the phosphoenolpyruvate carboxylase kinase activity generated during in vitro translation was Ca 2+-independent. These results demonstrate that phosphoenolpyruvate carboxylase kinase activity is regulated at the level of translatable mRNA in C 3, C 4 and CAM plants. 相似文献
4.
Summary CO 2 curves of photosynthesis and activities of the four C 4 enzymes and Ribulose bisphosphate carboxylase (RUBP c) were compared in two populations of the C 4 grass Echinochloa crus-galli from contrasting thermal environments (Québec and Mississippi). Analyses were conducted both before and after 14 h of chilling at 7°C under high light conditions. This comparison provides the opportunity to assess which steps of the C 4 pathway are more susceptible to become limiting at low temperatures. Both populations maintained, after chilling, a pattern of CO 2 fixation typical of C 4 plants with photosynthesis saturating at low external CO 2 concentrations. However, the chilling treatment led to reductions in carbon uptake and in the activities of the C 4 enzymes. RUBP c activity was not significantly affected by chilling. Reductions in photosynthesis and in C 4 enzyme activities following the chilling treatment were significantly larger for plants of the Mississippi population. The enzyme data suggest that two steps of the C 4 pathway, NADP +-malate dehydrogenase and pyruvate P i dikinase, are likely to be associated with the reduction of CO 2 uptake in C 4 plants under cool conditions. When the experiment was replicated under enriched atmospheric CO 2 (675 l l -1 CO 2), similar differences were observed between the two populations. CO 2 enrichment resulted in an increase of activity for phospho-enol-pyruvate carboxylase and NADP +-malate dehydrogenase while activities of phospho-enol-pyruvate carboxylase and NADP +-malic enzyme were less reduced following chilling. Such an interaction was not observed for gas exchange parameters but net photosynthesis was lower when plants were grown under enriched CO 2. 相似文献
5.
The mechanisms controlling the photosynthetic performance of C 4 plants at low temperature were investigated using ecotypes of Bouteloua gracilis Lag. from high (3000 m) and low (1500 m) elevation sites in the Rocky Mountains of Colorado. Plants were grown in controlled‐environment cabinets at a photon flux density of 700 μ mol m ?2 s ?1 and day/night temperatures of 26/16 °C or 14/7 °C. The thermal response of the net CO 2 assimilation rate ( A) was evaluated using leaf gas‐exchange analysis and activity assays of ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco), phosphoenolpyruvate carboxylase (PEPCase) and pyruvate,orthophosphate dikinase (PPDK). In both ecotypes, a reduction in measurement temperature caused the CO 2‐saturated rate of photosynthesis to decline to a greater degree than the initial slope of A versus the intercellular CO 2 response, thereby reducing the photosynthetic CO 2 saturation point. As a consequence, A in normal air was CO 2‐saturated at sub‐optimal temperatures. Ecotypic variation was low when grown at 26/16 °C, with the major difference between the ecotypes being that the low‐elevation plants had higher A; however, the ecotypes responded differently when grown at cool temperature. At temperatures below the thermal optimum, A in high‐elevation plants grown at 14/7 °C was enhanced relative to plants grown at 26/16 °C, while A in low‐elevation plants grown at 14/7 °C was reduced compared to 26/16 °C‐grown plants. Photoinhibition at low growth temperature was minor in both ecotypes as indicated by small reductions in dark‐adapted Fv/ Fm. In both ecotypes, the activity of Rubisco was equivalent to A below 17 °C but well in excess of A above 25 °C. Activities of PEPCase and PPDK responded to temperature in a similar proportion relative to Rubisco, and showed no evidence for dissociation that would cause them to become principal limitations at low temperature. Because of the similar temperature response of Rubisco and A, we propose that Rubisco is a major limitation on C 4 photosynthesis in B. gracilis below 17 °C. Based on these results and for theoretical reasons associated with how C 4 plants use Rubisco, we further suggest that Rubisco capacity may be a widespread limitation upon C 4 photosynthesis at low temperature. 相似文献
6.
Young leaves of salt-depleted Aeluropus litoralis Parl. plants show CO 2 fixation by the C 3-carbon fixation pathway. No detectable activity of phosphoenol pyruvate (PEP) carboxylase was found. When A. litoralis plants were exposed to a NaCl solution, the leaves showed a high activity of PEP carboxylase as well as a significant CO 2 fixation by the C 4-pathway. — Also in Zea mays L. and Chloris gayana Kunth., the presence of NaCl in the medium influences the balance between phosphoenol pyruvate carboxylase and ribulose-1,5-diphosphate carboxylase. 相似文献
7.
Abstract The pattern of photosynthetic carbon fixation by leaves of Amaranthus paniculatus L. (a C 4 plant) and Oryza sativa L. (a C 3 plant) varied with age. Younger leaves of A. paniculatus incorporated 14CO 2 into malate and aspartate while senescent leaves fixed predominantly into phosphoglycerate (PGA) and sugar phosphates. Only developing leaves of O. sativa formed malate/aspartate whereas mature and senescent leaves produced PGA/sugar phosphates as the initial labelled products. Correspondingly the ratio of phosphoenolpyruvate/ribulose bisphosphate (RuBP) carboxylase activities was higher in younger leaves of A. paniculatus and developing leaves of O. sativa than in older leaves. However, pulse chase experiments revealed that the main donors of carbon to end products, irrespective of leaf stage, were C 4 acids and PGA in A. paniculatus and O. sativa respectively. The results suggest that although an apparent change from initial β-carboxylation to RuBP carboxylation occurs during leaf ontogeny in both the plants, the overall leaf photosynthesis remains C 4 or C 3. The high rate of 14CO 2 incorporation into PGA/sugar phosphates by senescent leaves of A. paniculatus is suggested to be partly due to the increased intercellular spaces in their mesophyll, allowing greater access of CO 2 directly to RuBP carboxylase in the bundle sheath. 相似文献
8.
The leaf anatomy and certain photosynthetic properties of nitrate- and ammonia-grown plants of Moricandia arvensis (L.) DC., a species previously reported to be a C 3-C 4 intermediate, were investigated. Nitrate-grown plants had a high level of malate in the leaves while ammonia-grown plants had low levels of malate. In young leaves of nitrate-grown plants, there was a diurnal fluctuation of malate content, increasing during the day and decreasing during the night. Titratable acidity remained low in leaves of both nitrate- and ammonia-grown plants. In nitrate-grown plants, the activity of phosphoenolpyruvate (PEP) carboxylase was about 2-fold higher than in ammonia-grown plants, the latter having activity typical of C3 species. Also, in nitrate-grown plants, the ratio of activities of ribulose 1,5-bisphosphate (RuBP) carboxylase/PEP carboxylase was lower than in ammonia-grown plants. Nitrate reductase activities were higher in nitrate- than in ammonia-grown plants and the greatest activity was found in younger leaves. With nitrate-grown plants, during a pulse-chase experiment the label in malate, as a percentage of the total labeled products, increased from about 7% after a 10-second pulse with 14CO2 up to 17% during a 5-minute chase with 12CO2. The pattern of 14C labeling in various metabolites suggests the primary carboxylation is through RuBP carboxylase with a secondary carboxylation through PEP carboxylase. In similar experiments, with ammonia-grown plants, the percentage label in malate was only 0% to 4% with no increase in malate labeling during the chase period. The CO2 compensation point was lower in nitrate-grown than ammonia-grown plants. There was no evidence of Kranz-like anatomy in either the nitrate or ammonia-grown plants. Mitochondria of bundle-sheath cells were strikingly positioned along the inner tangential wall. This might allow the chloroplasts of these cells to fix the mitochondrial photorespired CO2 more effectively and contribute to the low CO2 compensation point in the species. Chloroplasts of bundle-sheath cells and contiguous mesophyll cells were similar in size and structure in plants grown on different media, although chloroplast thylakoids and stromata of the ammonia-grown plants stained more intensely than those of nitrate-grown plants. In addition, irregular clusters of phytoferritin particles occurred in the chloroplasts of the ammonia-grown plants. The results indicate that the substantial activity of PEP carboxylase, incorporation of CO2 into malate, the high malate content, and in part the relatively low CO2 compensation point in Moricandia arvensis may be accounted for by metabolism of nitrate rather than by a state of C3-C4 intermediacy. 相似文献
9.
Fruiting structures of a number of legumes including chickpea are known to carry out photosynthetic CO 2 assimilation, but the pathway of CO 2 fixation and particularly the role of phosphoenolpyruvate carboxylase (EC 4.1.1.31) in these tissues is not clear. Activities of some key enzymes of the Calvin cycle and C 4 metabolism, rates of 14CO 2 fixation in light and dark, and initial products of photosynthetic 14CO 2 fixation were determined in podwall and seedcoat (fruiting structures) and their subtending leaf in chickpea ( Cicer arietinum L.). Compared to activities of ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39) and other Calvin cycle enzyme, viz. NADP +-glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.13), NAD +-glyceraldehyde-3-phosphate dehydrogenase (EC 1.2.1.12) and ribulose-5-phosphate kinase (EC 2.7.1.19), the levels of phosphoenolpyruvate carboxylase and other enzymes of C 4 metabolism viz. NADP +-malate dehydrogenase (EC 1.1.1.82), NAD +-malate dehydrogenase (EC 1.1.1.37), NADP + malic enzyme (EC 1.1.1.40), NAD +-malic enzyme (EC 1.1.1.39), glutamate oxaloacetate transaminase (EC 2.6.1.1) and glutamate pyruvate transaminase (EC 2.6.1.2), were generally much higher in podwall and seedcoat than in the leaf. Podwall and seedcoat fixed 14CO 2 in light and dark at much higher rates than the leaf. Short-term assimilation of 14CO 2 by illuminated fruiting structures produced malate as the major labelled product with less labelling in 3-phosphoglycerate, whereas the leaf showed a major incorporation into 3-phosphoglycerate. It seems likely that the fruiting structures of chickpea utilize phosphoenolpyruvate carboxylase for recapturing the respired carbon dioxide. 相似文献
10.
Muhlenbergia sobolifera (Muhl.) Trin., a C 4 grass, occurs in understory habitats in the northeastern United States. Plants of M. sobolifera were grown at 23 and 30°C at 150 and 700 μmol photons m −2 s −1. The photosynthetic CO 2 compensation point, maximum CO 2 assimilation, dark respiration and the absorbed quantum use efficiency (QUE) were measured at 23 and 30°C at 2 and 20% O 2. Photosynthetic CO 2 compensation points ranged from 4 to 14mm 3 dm −3 CO 2 and showed limited O 2 sensitivity. The mean photosynthetic CO 2 compensation point of plants grown at 30°C (4·5 mm 3 dm −3) was 57% lower and 80% less inhibited by O 2 than that of plants grown at 23°C. Photosynthesis was similarly affected by growth temperature, with 70% more O 2 inhibition in plants grown at 23°C; suppression over all treatments ranging from 2 to 11%. Unlike typical C 4 species, plants of M. sobolifera from both temperature regimes exhibited higher CO 2 assimilation rates when grown at low light. Growth temperature and light also affected QUE; plants grown at low light and 23°C had the highest value (0·068 mol CO 2/mol quanta). Measurement temperature and growth light regime significantly affected dark respiration; however, O 2 did not affect QUE or dark respiration under any growth or measurement conditions. The results indicate that M. sobolifera is adapted to low PPFD, and that complete suppression of photorespiration is dependent upon high growth temperature. 相似文献
11.
The assimilation of 14CO 2 into the C 4 acids malate and aspartate by leaves of C 3, C 4 and C 3–C 4 intermediate Flaveria species was investigated near the CO 2 compensation concentration * in order to determine the potential role of phosphoenolpyruvate (PEP) carboxylase (EC 4.1.1.31) in reducing photorespiration in the intermediates. Relative to air concentrations of CO 2, the proportion of CO 2 fixed by PEP carboxylase at * increased in all six C 3–C 4 intermediate species examined. However, F. floridana J.R. Johnston and F. ramosissima Klatt were shown to be markedly less responsive to reduced external CO 2, with only about a 1.6-fold enhancement of CO 2 assimilation by PEP carboxylase, as compared to a 3.0- to 3.7-fold increase for the other C 3–C 4 species examined, namely, F. linearis Lag., F. anomala B.L. Robinson, F. chloraefolia A. Gray and F. pubescens Rydb. The C 3 species F. pringlei Gandoger and F. cronquistii A.M. Powell exhibited a 1.5- and 2.9-fold increase in labeled malate and aspartate, respectively, at *. Assimilation of CO 2 by PEP carboxylase in the C 4 species F. trinervia (Spreng.) C. Mohr, F. australasica Hook., and the C 4-like species F. brownii A.M. Powell was relatively insensitive to subatmospheric levels of CO 2. The interspecific variation among the intermediate Flaverias may signify that F. floridana and F. ramosissima possess a more C 4-like compartmentation of PEP carboxylase and ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39) between the mesophyll and bundle-sheath cells. Chasing recently labeled malate and aspartate with 12CO 2 for 5 min at * resulted in an apparent turnover of 25% and 30% of the radiocarbon in these C 4 acids for F. ramosissima and F. floridana, respectively. No substantial turnover was detected for F. linearis, F. anomala, F. chloraefolia or F. pubescens. With the exception of F. floridana and F. ramosissima, it is unlikely that enhanced CO 2 fixation by PEP carboxylase at the CO 2 compensation concentration is a major mechanism for reducing photorespiration in the intermediate Flaveria species. Moreover, these findings support previous related 14CO 2-labeling studies at air-levels of CO 2 which indicated that F. floridana and F. ramosissima were more C 4-like intermediate species. This is further substantiated by the demonstration that F. floridana PEP carboxylase, like the enzyme in C 4 plants, undergoes a substantial activation (2.2-fold) upon illuminating dark-adapted green leaves. In contrast, light activation was not observed for the enzyme in F. linearis or F. chloraefolia.Abbreviations and symbols PEP
phosphoenolpyruvate
- Rubisco
ribulose-1,5-bisphosphate carboxylase/oxygenase
-
CO 2 compensation concentration
- *
a subatmospheric level of CO 2 approximating
Published as Paper No. 8832, Journal Series, Nebraska Agricultural Research Division 相似文献
12.
Abstract CO 2 FIXATION IN CUSCUTA EPITHYMUM. — Seedlings of Cuscuta epithymum fixe approximately the same amount of C14O2 irrespectively of age, pigmentation, presence or absence of light. Examination by paper chromatography of the extracts of plants exposed to C11O2 revealed that most, or all, of the radioactivity is concentrated in the area of the organic acids and of the acidic amino acids. It is tentatively concluded that C. epithymum fixes carbon dioxide through a mechanism different from that involving ribulose-1,5-diphosphate carboxylase and carboxydismutase. 相似文献
13.
The potential for glycolate and glycine metabolism and the mechanism of refixation of photorespiratory CO 2 in leaves of C 4 plants were studied by parallel inhibitor experiments with thin leaf slices, different leaf cell types and isolated mitochondria of C 3 and C 4
Panicum species. CO 2 evolution by leaf slices of P. bisulcatum, a C 3 species, fed glycolate or glycine was light-independent and O 2-sensitive. The C 4
P. maximum and P. miliaceum leaf slices fed glycolate or glycine evolved CO 2 in the dark but not in the light. In C 4 species, dark CO 2 evolution was abolished by the addition of phosphoenolpyruvate (PEP) 4. The addition of maleate, a PEP carboxylase inhibitor, resulted in photorespiratory CO 2 efflux by C 4 leaf slices in the light also. However, PEP and maleate had no effect on either glycolate-dependent O 2 uptake by the C 4 leaf slices or on glycolate and glycine metabolism in C 3 leaf slices. The rate of photorespiratory CO 2 evolution in the C 3
Panicum species was 3 times higher than that observed with the C 4 species. The ratio of glycolate-dependent CO 2 evolution to O 2 uptake in both groups was 1:2. Isolated C 4 mesophyll protoplasts or their mitochondria did not metabolize glycolate or glycine. However, both C 3 mesophyll protoplasts and C 4 bundle sheath strands readily metabolized glycolate and glycine in a light-independent, O 2-sensitive manner, and the addition of PEP or maleate had no effect. C 4 bundle sheath- and C 3-mitochondria were capable of oxidizing glycine. This oxidation was linked to the mitochondrial electron transport chain, was coupled to three phosphorylation sites and was sensitive to electron transport inhibitors. C 4 bundle sheath- and C 3-mitochondrial glycine decarboxylation was stimulated by oxaloacetate and NAD had no effect. In marked contrast, mitochondria isolated from C 4 mesophyll cells were incapable of oxidizing or decarboxylating added glycine. The results suggest that in leaves of C 4 plants bundle sheath cells are the primary site of O 2-sensitive photorespiratory CO 2 evolution and the PEP carboxylase present in the mesophyll cells has the Potential for efficiently refixing CO 2 before it escapes out of the leaf. The relative role of the PEP carboxylase mediated CO 2 pump and reassimilation of photorespiratory CO 2 are discussed in relation to the apparent lack of photorespiration in leaves of C 4 species.Abbreviations BSA
bovine serum albumin
- Chl
chlorophyll
- PEP
phosphoenolpyruvate
- Rbu- P
2
ribulose 1,5-bisphosphate
- Rib-5-P
ribose-5-phosphate
- Ru-5-P
ribuluse-5-phosphate
- FCCP
carbonyl cyanide p-trifluoromethoxyphenylhydrazone
Journal Series Paper, New Jersey Agricultural Experiment Station 相似文献
14.
Plants with the C 3, C 4, and crassulacean acid metabolism (CAM) photosynthetic pathways show characteristically different discriminations against 13C during photosynthesis. For each photosynthetic type, no more than slight variations are observed within or among species. CAM plants show large variations in isotope fractionation with temperature, but other plants do not. Different plant organs, subcellular fractions and metabolises can show widely varying isotopic compositions. The isotopic composition of respired carbon is often different from that of plant carbon, but it is not currently possible to describe this effect in detail. The principal components which will affect the overall isotope discrimination during photosynthesis are diffusion of CO 2, interconversion of CO 2 and HCO ?3, incorporation of CO 2 by phosphoenolpyruvate carboxylase or ribulose bisphosphate carboxylase, and respiration. Theisotope fractionations associated with these processes are summarized. Mathematical models are presented which permit prediction of the overall isotope discrimination in terms of these components. These models also permit a correlation of isotope fractionations with internal CO 2 concentrations. Analysis of existing data in terms of these models reveals that CO 2 incorporation in C 3 plants is limited principally by ribulose bisphosphate carboxylase, but CO 2 diffusion also contributes. In C 4 plants, carbon fixation is principally limited by the rate of CO 2 diffusion into the leaf. There is probably a small fractionation in C 4 plants due to ribulose bisphosphate carboxylase. 相似文献
15.
Ulva, a common green seaweed, performs at the biochemical level as a typical C 3 plant. Over 90% of label was found in glycerate 3-phosphate following a 3 second 14C pulse in the light, and the label was subsequently transferred to sugars. Also, the level of ribulose-1,5-bisphosphate carboxylase activity in crude extracts was about 10 times higher than that of phosphoenolpyruvate carboxylase. Concerning gas exchange, photosynthetic rates of Ulva showed no O 2 sensitivity, indicating that photorespiratory CO 2 losses are repressed as in C 4 plants. This apparent anomaly could be explained by the efficient HCO 3− uptake system of Ulva which might concentrate CO 2 to the chloroplasts, thus suppressing the oxygenase activity of ribulose-1,5-bisphosphate carboxylase. 相似文献
16.
Incubation of the submersed aquatic macrophyte, Hydrilla verticillata Royle, for up to 4 weeks in growth chambers under winter-like or summer-like conditions produced high (130 to 150 μl CO 2/1) and low (6 to 8 μl CO 2/l) CO 2 compensation points (Γ), respectively. The activities of both ribulose bisphosphate (RuBP) and phosphoenolpyruvate (PEP) carboxylases increased upon incubation but the major increase was in the activity of PEP carboxylase under the summer-like conditions. This reduced the ratio of RuBP/PEP carboxylases from 2.6 in high Γ plants to 0.2 in low Γ plants. These ratios resemble the values in terrestrial C 3 and C 4 species, respectively. Kinetic measurements of the PEP carboxylase activity in high and low Γ plants indicated the Vmax was up to 3-fold greater in the low Γ plants. The Km (HCO 3 ?) values were 0.33 and 0.22 mM for the high and low Γ plants, respectively. The Km (PEP) values for the high and low Γ plants were 0.23 and 0.40 mM, respectively; and PEP exhibited cooperative effects. Estimated Km (Mg 2+) values were 0.10 and 0.22 mM for the high and low Γ plants, respectively. Malate inhibited both PEP carboxylase types similarly. The enzyme from low Γ plants was protected by malate from heat inactivation to a greater extent than the enzyme from high Γ plants. The results indicated that C 4 acid inhibition and protection were not reliable methods to distinguish C 3 and C 4 PEP carboxylases. The PEP carboxylase from low Γ plants was inhibited more by NaCl than that from hight Γ plants. These analyses indicated that Hydrilla PEP carboxylases had intermediate characteristics between those of terrestrial C 3 and C 4 species with the low Γ enzyme being different from the high Γ enzyme, and closer to a C 4 type. 相似文献
17.
Summary CO 2 exchange characteristics and the activity of the carboxylating enzymes phosphoenolpyruvate carboxylase (PEP-C, E.C. 4.1.1.31) and ribulose 1,5-bisphosphate carboxylase (RuBP-C, E.C. 4.1.1.39) during one year in the greenhouse and at two levels of light and temperature in growth chambers were determined in the C 3-C 4 intermediate species P. milioides Nees ex. Trin. These results were compared with those of P. bisulcatum Thumb. (C 3) and P. maximum Jacq. (C 4). Under all tested conditions, and even when the influence of leaf surface temperature on photosynthetic rates and CO 2 compensation points were measured, the biochemical and physiological behaviour of the C 3-C 4 intermediate was more similar to that of the C 3 plant than the C 4 species. The C 4 plant P. maximum, however, responded positively, mainly in terms of PEP-C activity and photosynthetic rate, to the regime of high light and temperature. The results presented indicate that in the C 3-C 4
Panicum grown in high light and temperature no direct relationships between a low CO 2 compesation point and superior growth are evident. It has still to be clarified why in nature a photosynthetic-photorespiratory pathway leading to an intermediate CO 2 compensation value has evolved in P. milioides. 相似文献
18.
The aim of this study was to characterise growth and photosynthetic capacity in plants adapted to long-term contrasting atmospheric
CO 2 concentrations ( C
a). Seeds of Agrostis canina L. ssp. monteluccii were collected from a natural CO 2 transect in central-western Italy and plants grown in controlled environment chambers at both ambient and elevated CO 2 (350 and 700 μmol mol −1) in nutrient-rich soil. Seasonal mean C
a at the source of the plant material ranged from 610 to 451 μmol CO 2 mol −1, derived from C 4 leaf stable carbon isotope discrimination (δ 13C). Under chamber conditions, CO 2 enrichment stimulated the growth of all populations. However, plants originating from elevated C
a exhibited higher initial relative growth rates (RGRs) irrespective of chamber CO 2 concentrations and a positive relationship was found between RGR and C
a at the seed source. Seed weight was positively correlated with C
a, but differences in seed weight were found to explain no more than 34% of the variation in RGRs at elevated CO 2. Longer-term experiments (over 98 days) on two populations originating from the extremes of the transect (451 and 610 μmol
CO 2 mol −1) indicated that differences in growth between populations were maintained when plants were grown at both 350 and 700 μmol
CO 2 mol −1. Analysis of leaf material revealed an increase in the cell wall fraction (CWF) in plants grown at elevated CO 2, with plants originating from high C
a exhibiting constitutively lower levels but a variable response in terms of the degree of lignification. In vivo gas exchange measurements revealed no significant differences in light and CO 2 saturated rates of photosynthesis and carboxylation efficiency between populations or with CO 2 treatment. Moreover, SDS-PAGE/ LISA quantification of leaf ribulose bisphosphate carboxylase/oxygenase (Rubisco) showed no
difference in Rubisco content between populations or CO 2 treatments. These findings suggest that long-term adaptation to growth at elevated CO 2 may be associated with a potential for increased growth, but this does not appear to be linked with differences in the intrinsic
capacity for photosynthesis.
Received: 16 August 1996 / Accepted: 19 October 1996 相似文献
19.
Incubation of the submersed aquatic macrophyte, Hydrilla vertieillata Royle, for up to 4 weeks in growth chambers under winter-like or summer-like conditions produced high (130 to 150 μl CO 2/l) and low (6 to 8 μl CO 2/l) CO 2 compensation points (Γ), respectively. The activities of both ribulose bisphosphate (RuBP) and phosphoenolpyruvate (PEP) carboxylases increased upon incubation but the major increase was in the activity of PEP carboxylase under the summer-like conditions. This reduced the ratio of RuBP/PEP carboxylases from 2.6 in high Γ plants to 0.2 in low Γ plants. These ratios resemble the values in terrestrial C 3 and C 4 species, respectively. Kinetic measurements of the PEP carboxylase activity in high and low Γ plants indicated the Vmax was up to 3-fold greater in the low Γ plants. The Km (HCO 3 -) values were 0.33 and 0.22 mM for the high and low Γ plants, respectively. The Km (PEP) values for the high and low Γ plants were 0.23 and 0.40 mM, respectively; and PEP exhibited cooperative effects. Estimated Km (Mg 2+) values were 0.10 and 0.22 mM for the high and low Γ plants, respectively. Malate inhibited both PEP carboxylase types similarly. The enzyme from low Γ plants was protected by malate from heat inactivation to a greater extent than the enzyme from high Γ plants. The results indicated that C 4 acid inhibition and protection were not reliable methods to distinguish C 3 and C 4 PEP carboxylases. The PEP carboxylase from low Γ plants was inhibited more by NaCl than that from high Γ plants. These analyses indicated that Hydrilla PEP carboxylases had intermediate characteristics between those of terrestrial C 3 and C 4 species with the low Γ enzyme being different from the high Γ enzyme, and closer to a C 4 type. 相似文献
20.
Activities of key enzymes of Calvin cycle and C 4 metabolism, rate of 14CO 2 fixation in light and dark and the initial products of photosynthetic 14CO 2 fixation were determined in flag leaf and different ear parts of wheat viz. pericarp, awn and glumes. Compared to the activities of RuBP carboxylase and other Calvin cycle enzymes viz. NADP-glyceraldehyde-3-phosphate dehydrogenase, NAD-glyceraldehyde-3-phosphate dehydrogenase and ribulose-5-phosphate kinase, the levels of PEP carboxylase and other enzymes of C 4 metabolism viz. NADP-malate dehydrogenase, NAD-malate dehydrogenase, NADP-malic enzyme, NAD-malic enzyme, glutamate oxaloacetate transaminase genase, NADP-malic enzyme, NAD-malic enzyme, glutamate oxaloacetate transaminase and glutamate pyruvate transaminase, were generally greater in ear parts than in the flag leaf. In contrast to CO 2 fixation in light, the various ear parts incorporated CO 2 in darkness at much higher rates than flag leaf. In short term assimilation of 14CO 2 by illuminated ear parts, most of the 14C was in malate with less in 3-phosphoglyceric acid, whereas flag leaves incorporated most into 3-phosphoglyceric acid. It seems likely that ear parts have the capability of assimilating CO 2 by the C 4 pathway of photosynthesis and utilise PEP carboxylase for recapturing the respired CO 2. 相似文献
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