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1.
Leaf CO 2 compensation points and stable hydrogen, oxygen and carbon isotope ratios were determined for Panicum species including C 3/C 4 intermediate photosynthesis plants, hybrids between C 3/C 4 intermediates and C 3 plants, C 3 and C 4 plants in the Panicum genus as well as several other C 3 and C 4 plants. C 3 plants had the highest compensation points, followed by hybrids, C 3/C 4 intermediates, and C 4 plants. δ 13C values of cellulose nitrate and saponifiable lipids from C 4 plants were about 10‰ higher than those observed for cellulose nitrate and saponifiable lipids of C 3/C 4 intermediates, hybrids, and C 3 plants. Oxygen isotope ratios of cellulose as well as those of leaf water were similar for all plants. There was substantial variability in the δD values of cellulose nitrate among the plants studied. In contrast, such variability was not observed in δD values of water distilled from the leaves, nor in the δD values of the saponifiable lipids. Variability in δD values of cellulose nitrate from C 3/C 4 intermediates, hybrids, C 3, and C 4 plants is due to fractionations occurring during biochemical reactions specific to leaf carbohydrate metabolism. 相似文献
2.
Carbon isotope ratios of mature leaves from the C 3 angiosperm root hemiparasites Striga hermonthica (Del.) Benth (−26.7‰) and S. asiatica (L.) Kuntze (−25.6‰) were more negative than their C 4 host, sorghum ( Sorghum bicolor [L.] Moench cv CSH1), (−13.5‰). However, in young photosynthetically incompetent plants of S. hermonthica this difference was reduced to less than 1‰. Differences between the carbon isotope ratios of two C 3-C 3 associations, S. gesnerioides (Willd.) Vatke— Vigna unguiculata (L.) Walp. and Oryza sativa L.— Rhamphicarpa fistulosa (Hochst.) Benth differed by less than 1‰. Theoretical carbon isotope ratios for mature leaves of S. hermonthica and S. asiatica, calculated from foliar gas exchange measurements, were −31.8 and −32.0‰, respectively. This difference between the measured and theoretical δ 13C-values of 5 to 6‰ suggests that even in mature, photosynthetically active plants, there is substantial input of carbon from the C 4 host. We estimate this to be approximately 28% of the total carbon in S. hermonthica and 35% in S. asiatica. This level of carbon transfer contributes to the host's growth reductions observed in Striga-infected sorghum. 相似文献
3.
Photorespiration rates in tissue cultures of a C 4 plant, Portulaca oleracea, were compared to those in tissue cultures of a C 3 plant, Streptanthus tortuosus. The C 4 plant tissue cultures have one-half to one-third the photorespiration rate of the C 3 plant tissue cultures and respond to varying O 2 concentrations in a manner typical of C 4 plants. The results suggest that the lack of detectable photorespiration in C 4 plants is not related to leaf anatomy. 相似文献
4.
Detached first leaves of 3-day-old corn seedlings ( Zea mays L. W64AxW183E) were incubated with nitrate in air or 100% O 2 in the light. Nitrate accumulation in the leaves was not depressed by O 2. NADH:nitrate reductase activity and enzyme protein, as measured with an enzyme-linked immunosorbent assay, increased in parallel during the 8 h nitrate treatment in air, but in O 2 the levels of enzyme activity and protein were depressed. NADH:nitrate reductase mRNA levels were the same in the air-and O 2-treated leaves. Total soluble protein levels in leaves were slightly depressed by O 2 and shifting from O 2 to an air environment increased the protein level. Incorporation of [ 35S]methionine during nitrate treatment revealed that total soluble protein and nitrate reductase protein synthesis were both depressed by the O 2 environment relative to air, but both recovered when leaves were shifted from O 2 to air. Although O 2 accelerated inactivation of nitrate reductase in vitro, the in vivo inactivation rate appeared to be too low to account for the depressed level of nitrate reductase activity in O 2-treated leaves. We concluded that O 2 inhibition of nitrate reductase biosynthesis in detached corn leaves was largely due to inhibition of total soluble protein synthesis at the level of translation. 相似文献
5.
Pyruvate orthophosphate dikinase (PPDK) was found in various immature seeds of C 3 plants (wheat, pea, green bean, plum, and castor bean), in some C 3 leaves (tobacco, spinach, sunflower, and wheat), and in C 4 (maize) kernels. The enzyme in the C 3 plants cross-reacts with rabbit antiserum against maize PPDK. Based on protein blot analysis, the apparent subunit size of PPDK from wheat seeds and leaves and from sunflower leaves is about 94 kdaltons, the same as that of the enzyme from maize, but is slightly less (about 90 kdaltons) for the enzyme from spinach and tobacco leaves. The amount of this enzyme per mg of soluble protein in C 3 seeds and leaves is much less than in C 4 leaves. PPDK is present in kernels of the C 4 plant, Zea mays in amounts comparable to those in C 4 leaves. Regulatory properties of the enzyme from C3 tissues (wheat) are similar to those of the enzyme from C4 leaves with respect to in vivo light activation and dark inactivation (in leaves) and in vivo cold lability (seeds and leaves). Following incorporation of 14CO2 by illuminated wheat pericarp and adjoining tissue for a few seconds, the labeled metabolites were predominantly products resulting from carboxylation of phosphoenolpyruvate, with lesser labeling of compounds formed by carboxylation of ribulose 1,5-bisphosphate and operation of the reductive pentose phosphate cycle of photosynthesis. PPDK may be involved in mechanisms of amino acid interconversions during seed development. 相似文献
6.
The δ 13C values of several seagrasses were considerably less negative than those of terrestrial C 3 plants and tended toward those of terrestrial C 4 plants. However, for Thalassia hemprichii (Ehrenb.) Aschers and Halophila spinulosa (R. Br.) Aschers, phosphoglycerate and other C 3 cycle intermediates predominated among the early labeled products of photosynthesis in 14C-labeled seawater (more than 90% at the earliest times) and the labeling pattern at longer times was brought about by the operation of the C 3 pathway. Malate and aspartate together accounted for only a minor fraction of the total fixed label at all times and the kinetic data of this labeling were not at all consistent with these compounds being early intermediates in seagrass photosynthesis. Pulse-chase 14C-labeling studies further substantiated these conclusions. Significant labeling of photorespiratory intermediates was observed in all experiments. The kinetics of total fixation of label during some steady-state and pulse-chase experiments suggested that there may be an intermediate pool of inorganic carbon of variable size closely associated with the leaves, either externally or internally. Such a pool may be one cause for the C 4-like carbon isotope ratios of seagrasses. 相似文献
7.
Effects of sodium application on sodium-deficient Amaranthus tricolor L. cv Tricolor seedlings were studied. Thirty-day-old A. tricolor seedlings grown without sodium received either 0.5 millimolar of NaCl or KCl, and the changes in the growth rate, chlorophyll concentration, photosynthetic oxygen evolution, and dark-oxygen consumption, and some enzyme activities were compared. Following the sodium treatment, the sodium concentration in the leaves increased from the initial value of 0.4 millimolar to 2 to 3 millimolar within 24 hours, and also the relative growth rate and O 2 evolution were enhanced within 24 hours. The stimulation of O 2 evolution was greater in the upper leaves than in the lower leaves. Although total chlorophyll concentration did not increase significantly, the increase in the chlorophyll a/b ratio was apparent within 24 hours. There were not significant increases in the C 4 photosynthetic enzyme activities; however, nitrate reductase activity increased by 350% by the sodium treatment within 24 hours, and this increase is considered not to be one of the consequences of the improved photosynthesis. Results suggest that the sodium treatment promoted CO 2 and nitrate assimilation resulting in the growth enhancement, and that sodium can be involved in some other functions than C 4 photosynthesis in A. tricolor plants. 相似文献
8.
Lower respiratory costs were hypothesized as providing an additional benefit in C 4 plants compared to C 3 plants due to less investment in proteins in C 4 leaves. Therefore, photosynthesis and dark respiration of mature leaves were compared between a number of C 4 and C 3 species. Although photosynthetic rates were generally greater in C 4 when compared to C 3 species, no differences were found in dark respiration rates of individual leaves at either the beginning or after 16 h of the dark period. The effects of nitrogen on photosynthesis and respiration of individual leaves and whole plants were also investigated in two species that occupy similar habitats, Amaranthus retroflexus (C 4) and Chenopodium album (C 3). For mature leaves of both species, there was no relationship between leaf nitrogen and leaf respiration, with leaves of both species exhibiting a similar rate of decline after 16 h of darkness. In contrast, leaf photosynthesis increased with increasing leaf nitrogen in both species, with the C 4 species displaying a greater photosynthetic response to leaf nitrogen. For whole plants of both species grown at different nitrogen levels, there was a clear linear relationship between net CO 2 uptake and CO 2 efflux in the dark. The dependence of nightly CO 2 efflux on CO 2 uptake was similar for both species, although the response of CO 2 uptake to leaf nitrogen was much steeper in the C 4 species, Amaranthus retroflexus. Rates of growth and maintenance respiration by whole plants of both species were similar, with both species displaying higher rates at higher leaf nitrogen. There were no significant differences in leaf or whole plant maintenance respiration between species at any temperature between 18 and 42°C. The data suggest no obvious differences in respiratory costs in C 4 and C 3 plants. 相似文献
9.
The possibility of altering CO 2 exchange of C 3-C 4 species by growing them under various CO 2 and O 2 concentrations was examined. Growth under CO 2 concentrations of 100, 350, and 750 micromoles per mole had no significant effect on CO 2 exchange characteristics or leaf anatomy of Flaveria pringlei (C 3), Flaveria floridana (C 3-C 4), or Flaveria trinervia (C 4). Carboxylation efficiency and CO 2 compensation concentrations in leaves of F. floridana developed under the different CO 2 concentrations were intermediate to F. pringlei and F. trinervia. When grown for 12 days at an O 2 concentration of 20 millimoles per mole, apparent photosynthesis was strongly inhibited in Panicum milioides (C 3-C 4) and to a lesser degree in Panicum laxum (C 3). In P. milioides, acute starch buildup was observed microscopically in both mesophyll and bundle sheath cells. Even after only 4 days exposure to 20 millimoles per mole O 2, the presence of starch was more pronounced in leaf cross-sections of P. milioides compared to those at 100 and 210 millimoles per mole. Even though this observation suggests that P. milioides has a different response to low O 2 with respect to translocation of photosynthate or sink activity than C 3 species, the concentration of total available carbohydrate increased in shoots of all species by 33% or more when grown at low O 2. This accumulation occurred even though relative growth rates of Festuca arundinacea (C 3) and P. milioides grown for 4 days at 210 millimoles per mole O 2, were inhibited 83 and 37%, respectively, when compared to plants grown at 20 millimoles per mole O 2. 相似文献
10.
Four species of the genus Flaveria, namely F. anomala, F. linearis, F. pubescens, and F. ramosissima, were identified as intermediate C 3-C 4 plants based on leaf anatomy, photosynthetic CO 2 compensation point, O 2 inhibition of photosynthesis, and activities of C 4 enzymes. F. anomala and F. ramosissima exhibit a distinct Kranz-like leaf anatomy, similar to that of the C 4 species F. trinervia, while the other C 3-C 4 intermediate Flaveria species possess a less differentiated Kranz-like leaf anatomy. Photosynthetic CO 2 compensation points of these intermediates at 30°C were very low relative to those of C 3 plants, ranging from 7 to 14 microliters per liter. In contrast to C 3 plants, net photosynthesis by the intermediates was not sensitive to O 2 concentrations below 5% and decreased relatively slowly with increasing O 2 concentration. Under similar conditions, the percentage inhibition of photosynthesis by 21% O 2 varied from 20% to 25% in the intermediates compared with 28% in Lycopersicon esculentum, a typical C 3 species. The inhibition of carboxylation efficiency by 21% O 2 varied from 17% for F. ramosissima to 46% for F. anomala and were intermediate between the C 4 (2% for F. trinervia) and C 3 (53% for L. esculentum) values. The intermediate Flaveria species, especially F. ramosissima, have substantial activities of the C 4 enzymes, phosphoenolpyruvate carboxylase, pyruvate, orthophosphate dikinase, NADP-malic enzyme, and NADP-malate dehydrogenase, indicating potential for C 4 photosynthesis. It appears that these Flaveria species may be true biochemical C 3-C 4 intermediates. 相似文献
11.
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
12.
Photosynthetic characteristics were studied in several F 1 hybrids between C 4 and C 3-C 4 species of Flaveria. Stable carbon isotope ratios, O 2 inhibition of apparent photosynthesis, and phosphoenolpyruvate carboxylase activities in the hybrids were similar to the means for the parents. Values of CO 2 compensation concentrations were nearer to those of the C 4 parent and apparent photosynthesis was below that of both parents, being only 60 and 74% of that of the lowest (C 3-C 4) parent in two experiments. Reductions of CO 2 compensation concentration and O 2 inhibition of apparent photosynthesis as well as increases in carbon isotope ratios and phosphoenolpyruvate carboxylase activities compared to values in C 3-C 4 species suggest transfer of a limited degree of C 4 photosynthesis to the F 1 hybrids. However, the lower apparent photosynthesis of the hybrids suggests that transfer of C 4 characteristics to non-C 4 species is detrimental unless characteristics associated with C 4 photosynthesis are fully developed. There was a highly significant negative correlation ( r = −0.90) between CO 2 compensation concentration and the logarithm of phosphoenolpyruvate carboxylase activity in the parents and hybrids, suggesting involvement of this enzyme in controlling the CO 2 compensation concentration. Although bundle-sheath cells were more developed in leaves of hybrids than in C 3-C 4 parents, they appeared to contain lower quantities of organelles than those of the C 4 parent. Reduced quantities of organelles in bundle-sheath cells could indicate incomplete compartmentation of partial pathways of the C 4 cycle in the hybrids. This may mean that the reduction of CO 2 compensation and O 2 inhibition of apparent photosynthesis relative to the C 3-C 4 parents is less dependent on fully developed Kranz anatomy than is increased apparent photosynthesis. 相似文献
13.
Exposure of leaf sections from 2-week-old seedlings of sorghum ( Sorghum bicolor L.) (C 4 plant), corn ( Zea mays L.) (C 4), peanut ( Arachis hypogaea L.) (C 3 plant), and soybean ( Glycine max L.) (C 3) to 40 or 45°C for up to 4 hours resulted in significant increases in the levels of 102 kilodalton (C 4), 52 kilodalton (C 3 and C 4), and 15 kilodalton (C 3 and C 4) polypeptides. These proteins comigrated, respectively, with authentic phosphoenolpyruvate carboxylase (PEPC) and the large (RLSU) and small (RSSU) subunits of ribulose-1,5-bisphosphate carboxylase (Rubisco) during both one- and two-dimensional SDS-PAGE and reacted with antisera raised against these enzymes. After 4 hours at 50°C, levels of the polypeptides either remained relatively stable (PEPC, RLSU) or increased (RSSU) in sorghum and peanut (plants native to hot climates). In corn and soybean (plants native to temperate climates), levels of the proteins either fell sharply (corn) or showed strong evidence of incomplete processing and/or aggregation (soybean). In addition to changes in levels of the proteins, the activities of PEPC and Rubisco in extracts of leaves exposed to 50°C fell by 84% and 11% of their respective control values in sorghum and by 54% each in peanut. In corn and soybean, the activities of both enzymes were depressed at 40°C, with measured values at 50°C not exceeding 5% of those from the nonstressed controls. 相似文献
14.
Phosphoenolpyruvate carboxylase (PEPC) from several C 3 plants was compared to maize PEPC by immunoblotting using an antibody against maize PEPC and by peptide mapping. In C 3 gramineous plants, PEPCs of slightly different monomeric sizes were detected as two bands for wheat and barley leaves, as three bands for etiolated maize leaves and as four bands for rice leaves by SDS-polyacrylamide gel electrophoresis and immunoblotting, whereas only one PEPC band was detected for maize leaves, a C 4 plant, or tobacco leaves, a dicotyledonous C 3 plant. The peptide fragment patterns of the lower molecular weight PEPC (major band in immunoblotting) in wheat leaves was similar to that of maize PEPC in peptide mapping by protein staining or by immunological detection, but the upper one (minor band) had a different pattern from the lower one in peptide mapping by immunological detection and few peptide fragments from this were recognized by the anti-(maize) PEPC antibody. These results suggest that there are multiple forms of PEPC subunits in the gramineous plants tested, and the major PEPC has a primary structure similar to that of maize PEPC. To obtain information about the expression of PEPCs in C 3 plants, changes in the amount of PEPC protein were investigated during the greening of rice and wheat seedlings. Judging from the regulation by light, there were two types of PEPCs in greening rice seedlings, one induced by light and the other reduced by it. Greening wheat seedlings also show a PEPC band induced by light. These findings indicate that some PEPCs in C 3 gramineous plants not only have structures similar to that of maize PEPC, but also are regulated by light in a similar manner. 相似文献
15.
The carbon atoms of glucose and malate in C 4 plants are 2 to 3‰ enriched in 12C with respect to atmospheric CO 2; whereas these intermediates in C 3 plants are 15 to 18‰ enriched with 12C with respect to atmospheric CO 2. The enzymatic synthesis of malate from phosphoenolpyruvate and bicarbonate in preparations of leaves of Sorghum bicolor, Haygrazer result in a carbon isotope fractionation of about 3‰. The enzymatic synthesis of phosphoglyceric acid from ribulose 1,5-diP and CO 2 in these preparations (contaminated with carbonic anhydrase) at 24 C and 37 C result in a carbon isotope fractionation of 33.7‰ and 18.3‰, respectively. These data are consistent with the conclusion that the small enrichment of 12C in the carbon atoms of malate and glucose (with respect to atmospheric CO 2) in leaves of Sorghum bicolor, Haygrazer occurs at the phosphoenolpyruvate carboxylase step. 相似文献
16.
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
17.
Chlorate-resistant Nicotiana plumbaginifolia (cv Viviani) mutants were found to be deficient in the nitrate reductase apoprotein (NR −nia). Because they could not grow with nitrate as sole nitrogen source, they were cultivated as graftings on wild-type Nicotiana tabacum plants. The grafts of mutant plants were chlorotic compared to the grafts of wild type. Mutant leaves did not accumulate nitrogen and nitrate but contained less malate and more glutamine than wild leaves. They exhibited a slight increase of the proportion of the light-harvesting chlorophyll a/ b protein complexes and a lowering of the efficiency of energy transfer between these complexes and the active centers. After a 3 second 14CO 2 pulse, the total 14C incorporation of the mutant leaves was approximately 20% of that of the control. The 14C was essentially recovered in ribulose bisphosphate in these plants. It was consistent with a decline of ribulose bisphosphate carboxylase activity observed in the mutant. After a 3 second 14CO 2 pulse followed by a 60 second chase with normal CO 2, 14C was mainly accumulated in starch which was labeled more in the mutant than in the wild type. These results confirm the observation that in the nitrate reductase deficient leaves, chloroplasts were loaded with large starch inclusions preceding disorganization of the photosynthetic apparatus. 相似文献
18.
Effect of nitrate on the nitrogenase (C 2H 2-reduction) activity, growth of nodule tissue accumulation of nitrate and nitrate reductase activity in 4-weeks-old nodulated peas ( Pisum sativum l.) was investigated. A relatively slow decrease of the total nitrogenase activity (μmol C 2H 4 per root per h), as compared with plants cultivated without nitrate, was due to both retardation of further growth of the nodule tissue and to a decrease of their specific nitrogenase activity (μmol C 2H 4 per g f.wt. per h). However, an absolute and pronounced decrease of both nitrogenase activities occurred only 4 or 7 d after the application of nitrate. The addition of nitrate led to its rapid accumulation in the nodule and leaf tissue with a simultaneous induction of the nitrate reductase activity. The nitrogenase activity was not completely inhibited even after a 7-d cultivation with 280 ppm NO 3 ?-N in the nutrient medium and after accumulation of up to 180 ppm NO 3 ?-N f.wt. in the nodule tissue. The results obtained indicate that the “photosynthate deprivation” reflects competition between assimilation of nitrate and fixation of dinitrogen. 相似文献
19.
A transient CO 2 burst is exhibited by irradiated leaves of the C 3 plant geranium ( Pelargonium X hortorum, Bailey) after the irradiance is quickly lowered. The light CO 2 burst appears to be related to photorespiration because of its irradiance dependency and its sensitivity to other environmental components such as CO 2 and O 2 concentration. The term post-lower-irradiance CO 2 burst or PLIB is used to describe the phenomenon. The PLIB appears to be a quantitative measurement of photorespiration with intact geranium leaves. The PLIB has been observed with intact leaves of other C 3 plants but not with C 4 leaves. Therefore, it is proposed that, after maximizing intact leaf photosynthetic rates and leaf chamber gas measuring conditions, photorespiration can be measured with intact C 3 leaves such as geranium as a transient post-lower-irradiance CO 2 burst. 相似文献
20.
The uptake of mercury vapor by six gramineous plant species was compared under uniform conditions using a whole-plant chamber and 203Hg-labeled mercury at a low atmospheric concentration. Mean Hg uptake by leaves of the C 3 species oats ( Avena sativa), barley ( Hordeum vulgare), and wheat ( Triticum aestivum) was 5 times greater than that by leaves of the C 4 species corn ( Zea mays), sorghum ( Sorghum bicolor), and crabgrass ( Digitaria sanguinalis). Although there was a difference in resistances associated with vapor entry into the leaves, as shown by estimates of gas exchange, the differential uptake by C 3 and C 4 species was largely attributable to internal resistances to Hg vapor binding. The nature of the internal resistances and the site or sites of Hg vapor binding remain unspecified. 相似文献
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