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1.
Kinetic properties of phosphoenolpyruvate carboxylase from c(3), c(4), and c(3)-c(4) intermediate species of flaveria (asteraceae) 总被引:3,自引:3,他引:0
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Flaveria cronquistii (C3), F. chloraefolia (C3-C4), F. floridana (C3-C4), F. pubescens (C3-C4), F. anomala (C3-C4), F. linearis (C3-C4), F. brownii (C4), F. palmeri (C4), F. trinervia (C4) and F. australasica (C4), comprising 10 out of the 21 known species of the genus Flaveria (Asteraceae), were included in a comparative study of the kinetic and regulatory properties of green leaf phosphoenolpyruvate (PEP) carboxylase. At least three kinetically distinct enzyme-forms were identified on the basis of their affinities for PEP and the degree of allosterism with respect to this substrate. The kinetic properties of PEP carboxylase of most of the species seemingly were modified in vivo depending on the growth conditions of the plants. Km(PEPfree)-values of the enzyme from the five C3-C4 intermediate species ranged from 6 micromolar (F. chloraefolia, low light-grown) to 38 micromolar (F. pubescens, high light-grown). In contrast, the Km for PEP of PEP carboxylase from the C3 species F. cronquistii (13 micromolar) apparently was not influenced by growth conditions. The response of the enzyme from the C3 and C3-C4 species was hyperbolic in all cases. A second isoform with a lower affinity for PEP (88-100 micromolar), but also hyperbolic kinetics was found in the C4 species F. brownii, whereas in the three other C4 species examined a PEP carboxylase with a still lower affinity for PEP (187-221 micromolar) and sigmoidal kinetics was present. These isozyme-related kinetic data were supported by analyses of the elution behavior of the enzyme during anion-exchange chromatography on DEAE-Trisacryl M. The results are discussed with respect to the evolution of C4 photosynthesis in the Flaveria genus. 相似文献
2.
Reduced Apparent Photorespiration by the C(3)-C(4) Intermediate Species, Moricandia arvensis and Panicum milioides 总被引:2,自引:2,他引:0
The CO2/O2 specificity factor of sucrose gradient purified ribulose 1,5-bisphosphate carboxylase/oxygenase from the C3-C4 intermediate plants Moricandia arvensis (79 ± 1) and Panicum milioides (89 ± 2) was similar to the respective values of the enzyme from the closely related C3 species, Moricandia foetida (80 ± 5) and Panicum laxum (86 ± 2). Thus, the kinetic properties of this bifunctional enzyme do not explain the reduced rates of photorespiration exhibited by either of these intermediate species. 相似文献
3.
Leaf anatomy of c(3)-c(4) species as related to evolution of c(4) photosynthesis 总被引:3,自引:2,他引:1
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This study was undertaken to examine the degree of Kranz anatomy development in the species intermediate to C3 and C4 types (C3-C4) in Panicum, Neurachne, Flaveria, and Moricandia. In each genus, C3 and/or C4 species were used for comparison. Leaf transections from each species were examined by light and transmission electron microscopy. The percentages of leaf photosynthetic cell profiles partitioned to bundle sheaths were higher in C4 than in C3 species, while C3-C4 species tended to be in between. However, percentages for C3-C4 species in Moricandia and some C3-C4Flaveria species were not greater than C3. When expressed on a cell profile area basis, C3-C4 species partitioned more photosynthetic tissue to bundle sheaths than C3 species in Moricandia, but not in Flaveria. Neurachne minor S. T. Blake (C3-C4) partitioned a very small portion of cell profile area to the inner bundle sheaths (5%) compared to Neurachne munroi F. Muell (C4) (21%). The percentage of organelles partitioned to bundle sheaths was much greater in C3-C4 than in C3 species. The average C3 percentages for mitochondria plus peroxisomes were 19, 8, and 19.5% for Neurachne, Flaveria, and Moricandia, respectively, compared to 41, 29, and 46.5% for the C3-C4 species. The CO2 compensation concentration was negatively related to the partitioning of tissue to bundle sheaths and to the percentage of organelles in bundle sheaths. It is concluded that all of the C3-C4 species examined have developed some degree of Kranz anatomy and that this altered anatomy is involved in their reduced apparent photorespiration. 相似文献
4.
Effect of pH on the Kinetic Parameters of NADP-Malic Enzyme from a C(4)Flaveria (Asteraceae) Species
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We have used the pH variation in the kinetic parameters with respect to malate of NADP-malic enzyme purified from the C4 species, Flaveria trinervia, to compare the pK values of its functional groups with those for the pigeon liver NADP-malic enzyme (MI Schimerlik, WW Cleland [1977] Biochemistry 16: 576-583) and the plant NAD-malic enzyme (KO Willeford, RT Wedding [1987] Plant Physiol 84: 1084-1087). Like the other enzymes, the C4 enzyme has a group with a pK of about 6.0 (6.6 for the C4 enzyme), as indicated from plots of the log Vmax/Km (Vmax = maximum rate of catalysis) versus pH, which must lose a proton for malate binding and subsequent catalysis. The optimum ionization for the C4 enzyme-NADP-Mg2+ complex occurs at pH 7.1 to 7.5. From pH 7.5 to 8.4, the Km increases, but Vmax remains constant. The log Vmax/Km plot in this pH range indicates a group with a pK of about 7.7. The other malic enzymes exhibit a similar pK. Above pH 8.4, deprotonation leads to a marked increase in Km and a decrease in Vmax for the C4 enzyme. As in the case of the animal enzyme, the log Vmax/Km plot for the C4 enzyme appears to approach a slope of two. The curve suggests an average pK of 8.4 for the groups involved, while the animal enzyme exhibits an average pK of 9.0. The NAD-malic enzyme does not exhibit any pK values at these high pK values. We hypothesize that the putative groups with the high pK values may be at least partially responsible for the ability of the C4 NADP-malic enzyme to maintain high activity at pH 8.0 in illuminated chloroplasts. 相似文献
5.
Multiple forms of plant phosphoenolpyruvate carboxylase associated with different metabolic pathways 总被引:5,自引:3,他引:2
A detailed comparison of green leaf phosphoenolpyruvate carboxylases from the C4-species Atriplex spongiosa and the C3-species Atriplex hastata revealed significant physical and kinetic differences. The two alloenzymes can be separated by anion exchange chromatography but have comparable molecular weights (350,000). Maximal velocity estimates were 38.0 and 1.48 micromoles per minute per milligram of chlorophyll for the carboxylases of A. spongiosa and A. hastata, respectively. Km phosphoenolpyruvate estimates were 0.49 and 0.08 mm for the C4A. spongiosa and C3A. hastata and the Km Mg estimates were 0.33 mm for the C4 species and 0.017 mm for the C3 species. The activity of the phosphoenolpyruvate carboxylase of A. spongiosa is more sensitive to chloride and phosphate than the phosphoenolpyruvate carboxylase of A. hastata, but both are equally sensitive to Mg chelating substances such as ATP, ADP, and citrate if assayed at their respective Km Mg values. A survey of the phosphoenolpyruvate carboxylases from 18 C4 and C3 species resulted in mean maximal velocity estimates of 29.0 ± 13.2 and 1.50 ± 0.57 micromoles per minute per milligram of chlorophyll for the C4 species and C3 species, respectively. Km phosphoenolpyruvate estimates were 0.59 ± 0.35 mm and 0.14 ± 0.07 mm for the C4 and C3, and Km Mg estimates were 0.50 ± 0.30 and 0.097 ± 0.057 mm for C4 and C3. All differences between means were significant at the 0.01 confidence level, supporting our hypothesis that the phosphoenolpyruvate carboxylase alloenzymes of C4 and C3 plants are functionally different and are associated with different photosynthetic roles. Both function in the photosynthetic production of C4 acids, the phosphoenolpyruvate carboxylase of C4 species largely producing malate or aspartate (or both) as a photosynthetic intermediate and the phosphoenolpyruvate carboxylase of C3 species producing malate or aspartate (or both) as a photosynthetic product. 相似文献
6.
Photosynthesis of F(1) Hybrids between C(4) and C(3)-C(4) Species of Flaveria 总被引:14,自引:6,他引:8
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Brown RH Bassett CL Cameron RG Evans PT Bouton JH Black CC Sternberg LO Deniro MJ 《Plant physiology》1986,82(1):211-217
Photosynthetic characteristics were studied in several F1 hybrids between C4 and C3-C4 species of Flaveria. Stable carbon isotope ratios, O2 inhibition of apparent photosynthesis, and phosphoenolpyruvate carboxylase activities in the hybrids were similar to the means for the parents. Values of CO2 compensation concentrations were nearer to those of the C4 parent and apparent photosynthesis was below that of both parents, being only 60 and 74% of that of the lowest (C3-C4) parent in two experiments. Reductions of CO2 compensation concentration and O2 inhibition of apparent photosynthesis as well as increases in carbon isotope ratios and phosphoenolpyruvate carboxylase activities compared to values in C3-C4 species suggest transfer of a limited degree of C4 photosynthesis to the F1 hybrids. However, the lower apparent photosynthesis of the hybrids suggests that transfer of C4 characteristics to non-C4 species is detrimental unless characteristics associated with C4 photosynthesis are fully developed. There was a highly significant negative correlation (r = −0.90) between CO2 compensation concentration and the logarithm of phosphoenolpyruvate carboxylase activity in the parents and hybrids, suggesting involvement of this enzyme in controlling the CO2 compensation concentration. Although bundle-sheath cells were more developed in leaves of hybrids than in C3-C4 parents, they appeared to contain lower quantities of organelles than those of the C4 parent. Reduced quantities of organelles in bundle-sheath cells could indicate incomplete compartmentation of partial pathways of the C4 cycle in the hybrids. This may mean that the reduction of CO2 compensation and O2 inhibition of apparent photosynthesis relative to the C3-C4 parents is less dependent on fully developed Kranz anatomy than is increased apparent photosynthesis. 相似文献
7.
Enzymic Properties of Ribulose-1,5-bisphosphate Carboxylase/Oxygenase Purified from Rice Leaves 总被引:5,自引:1,他引:4
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The enzymic properties of ribulose 1,5-bisphosphate (RuBP) carboxylase/oxygenase purified from rice (Oryza sativa L.) leaves were studied. Rice RuBPcarboxylase, activated by preincubation with CO2 and Mg2+ like other higher plant carboxylases, had an activation equilibrium constant (KcKMg) of 1.90 × 105 to 2.41 × 105 micromolar2 (pH 8.2 and 25°C). Kinetic parameters of carboxylation and oxygenation catalyzed by the completely activated enzyme were examined at 25°C and the respective optimal pHs. The Km(CO2), Km(RuBP), and Vmax values for carboxylation were 8 micromolar, 31 micromolar, and 1.79 units milligram−1, respectively. The Km(O2), Km(RuBP), and Vmax values for oxygenation were 370 micromolar, 29 micromolar, and 0.60 units milligram−1, respectively.
Comparison of rice leaf RuBP carboxylase with other C3 plant carboxylases showed that it had a relatively high affinity for CO2 but the lowest catalytic turnover number (Vmax) among the species examined.
相似文献8.
Bhaskarrao Chinthapalli Chitra Raghavan O. Bläsing P. Westhoff A.S. Raghavendra 《Photosynthetica》2001,38(3):415-419
Phosphoenolpyruvate carboxylase (PEPC) was purified from leaves of four species of Alternanthera differing in their photosynthetic carbon metabolism: Alternanthera sessilis (C3), A. pungens (C4), A. ficoides and A. tenella (C3-C4 intermediates or C3-C4). The activity and properties of PEPC were examined at limiting (0.05 mM) or saturating (10 mM) bicarbonate concentrations.
The Vmax as well as Km values (for Mg2+ or PEP) of PEPC from A. ficoides and A. tenella (C3-C4 intermediates) were in between those of C3 (A. sessilis) and C4 species (A. pungens). Similarly, the sensitivity of PEPC to malate (an inhibitor) or G-6-P (an activator) of A. ficoides and A. tenella (C3-C4) was also of intermediate status between those of C3 and C4 species of A. sessilis and A. pungens, respectively. In all the four species, the maximal activity (Vmax), affinity for PEP (Km), and the sensitivity to malate (KI) or G-6-P (KA) of PEPC were higher at 10 mM bicarbonate than at 0.05 mM bicarbonate. Again, the sensitivity to bicarbonate of PEPC from
C3-C4 intermediates was in between those of C3- and C4-species. Thus the characteristics of PEPC of C3-C4 intermediate species of Alternanthera are intermediate between C3- and C4-type, in both their kinetic and regulatory properties. Bicarbonate could be an important modulator of PEPC, particularly
in C4 plants.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
9.
Photosynthetic Characteristics of C(3)-C(4) Intermediate Flaveria Species : I. Leaf Anatomy, Photosynthetic Responses to O(2) and CO(2), and Activities of Key Enzymes in the C(3) and C(4) Pathways 总被引:10,自引:9,他引:1
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Four species of the genus Flaveria, namely F. anomala, F. linearis, F. pubescens, and F. ramosissima, were identified as intermediate C3-C4 plants based on leaf anatomy, photosynthetic CO2 compensation point, O2 inhibition of photosynthesis, and activities of C4 enzymes. F. anomala and F. ramosissima exhibit a distinct Kranz-like leaf anatomy, similar to that of the C4 species F. trinervia, while the other C3-C4 intermediate Flaveria species possess a less differentiated Kranz-like leaf anatomy. Photosynthetic CO2 compensation points of these intermediates at 30°C were very low relative to those of C3 plants, ranging from 7 to 14 microliters per liter. In contrast to C3 plants, net photosynthesis by the intermediates was not sensitive to O2 concentrations below 5% and decreased relatively slowly with increasing O2 concentration. Under similar conditions, the percentage inhibition of photosynthesis by 21% O2 varied from 20% to 25% in the intermediates compared with 28% in Lycopersicon esculentum, a typical C3 species. The inhibition of carboxylation efficiency by 21% O2 varied from 17% for F. ramosissima to 46% for F. anomala and were intermediate between the C4 (2% for F. trinervia) and C3 (53% for L. esculentum) values. The intermediate Flaveria species, especially F. ramosissima, have substantial activities of the C4 enzymes, phosphoenolpyruvate carboxylase, pyruvate, orthophosphate dikinase, NADP-malic enzyme, and NADP-malate dehydrogenase, indicating potential for C4 photosynthesis. It appears that these Flaveria species may be true biochemical C3-C4 intermediates. 相似文献
10.
The kinetic properties of pyruvate kinase (ATP:pyruvate-phosphotransferase, EC 2.7.1.40) from Streptococcus lactis have been investigated. Positive homotropic kinetics were observed with phosphoenolpyruvate and adenosine 5′-diphosphate, resulting in a sigmoid relationship between reaction velocity and substrate concentrations. This relationship was abolished with an excess of the heterotropic effector fructose-1,6-diphosphate, giving a typical Michaelis-Menten relationship. Increasing the concentration of fructose-1,6-diphosphate increased the apparent Vmax values and decreased the Km values for both substrates. Catalysis by pyruvate kinase proceeded optimally at pH 6.9 to 7.5 and was markedly inhibited by inorganic phosphate and sulfate ions. Under certain conditions adenosine 5′-triphosphate also caused inhibition. The Km values for phosphoenolpyruvate and adenosine 5′-diphosphate in the presence of 2 mM fructose-1,6-diphosphate were 0.17 mM and 1 mM, respectively. The concentration of fructose-1,6-diphosphate giving one-half maximal velocity with 2 mM phosphoenolpyruvate and 5 mM adenosine 5′-diphosphate was 0.07 mM. The intracellular concentrations of these metabolites (0.8 mM phosphoenolpyruvate, 2.4 mM adenosine 5′-diphosphate, and 18 mM fructose-1,6-diphosphate) suggest that the pyruvate kinase in S. lactis approaches maximal activity in exponentially growing cells. The role of pyruvate kinase in the regulation of the glycolytic pathway in lactic streptococci is discussed. 相似文献
11.
Pathology-related substitutions in human mitochondrial tRNA(Ile) reduce precursor 3' end processing efficiency in vitro
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The human mitochondrial genome encodes 22 tRNAs interspersed among the two rRNAs and 11 mRNAs, often without spacers, suggesting that tRNAs must be efficiently excised. Numerous maternally transmitted diseases and syndromes arise from mutations in mitochondrial tRNAs, likely due to defect(s) in tRNA metabolism. We have systematically explored the effect of pathogenic mutations on tRNAIle precursor 3′ end maturation in vitro by 3′-tRNase. Strikingly, four pathogenic tRNAIle mutations reduce 3′-tRNase processing efficiency (Vmax / KM) to ~10-fold below that of wild-type, principally due to lower Vmax. The structural impact of mutations was sought by secondary structure probing and wild-type tRNAIle precursor was found to fold into a canonical cloverleaf. Among the mutant tRNAIle precursors with the greatest 3′ end processing deficiencies, only G4309A displays a secondary structure substantially different from wild-type, with changes in the T domain proximal to the substitution. Reduced efficiency of tRNAIle precursor 3′ end processing, in one case associated with structural perturbations, could thus contribute to human mitochondrial diseases caused by mutant tRNAs. 相似文献
12.
C(3)-C(4) Intermediate Species in Alternanthera (Amaranthaceae) : Leaf Anatomy, CO(2) Compensation Point, Net CO(2) Exchange and Activities of Photosynthetic Enzymes
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Two naturally occurring species of the genus Alternanthera, namely A. ficoides and A. tenella, were identified as C3-C4 intermediates based on leaf anatomy, photosynthetic CO2 compensation point (Γ), O2 response of г, light intensity response of г, and the activities of key enzymes of photosynthesis. A. ficoides and A. tenella exhibited a less distinct Kranz-like leaf anatomy with substantial accumulation of starch both in mesophyll and bundle sheath cells. Photosynthetic CO2 compensation points of these two intermediate species at 29°C were much lower than in C3 plants and ranged from 18 to 22 microliters per liter. Although A. ficoides and A. tenella exhibited similar intermediacy in г, the apparent photorespiratory component of O2 inhibition in A. ficoides is lower than in A. tenella. The г progressively decreases from 35 microliters per liter at lowest light intensity to 18 microliters per liter at highest light intensity in A. tenella. It was, however, constant in A. ficoides at 20 to 25 microliters per liter between light intensities measured. The rates of net photosynthesis at 21% O2 and 29°C by A. ficoides and A. tenella were 25 to 28 milligrams CO2 per square decimeter per hour which are intermediate between values obtained for Tridax procumbens and A. pungens, C3 and C4 species, respectively. The activities of key enzymes of C4 photosynthesis, phosphoenolpyruvate carboxylase, pyruvate Pi dikinase, NAD malic enzyme, NADP malic enzyme and phosphoenolpyruvate carboxykinase in the two intermediates, A. ficoides and A. tenella are very low or insignificant. Results indicated that the relatively low apparent photorespiratory component in these two species is presumably the basis for the C3-C4 intermediate photosynthesis. 相似文献
13.
The weedy species Parthenium hysterophorus (Asteraceae) possesses a Kranz-like leaf anatomy. The bundle sheath cells are thick-walled and contain numerous granal chloroplasts, prominent mitochondria, and peroxisomes, all largely arranged in a centripetal position. Both mesophyll and bundle sheath chloroplasts accumulate starch. P. hysterophorus exhibits reduced photorespiration as indicated by a moderately low CO2 compensation concentration (20-25 microliters per liter at 30°C and 21% O2) and by a reduced sensitivity of net photosynthesis to 21% O2. In contrast, the related C3 species P. incanum and P. argentatum (guayule) lack Kranz anatomy, have higher CO2 compensation concentrations (about 55 microliters per liter), and show a greater inhibition of photosynthesis by 21% O2. Furthermore, in P. hysterophorus the CO2 compensation concentration is relatively less sensitive to changes in O2 concentrations and shows a biphasic response to changing O2, with a transition point at about 11% O2. Based on these results, P. hysterophorus is classified as a C3-C4 intermediate. The activities of diagnostic enzymes of C4 photosynthesis in P. hysterophorus were very low, comparable to those observed in the C3 species P. incanum (e.g. phosphoenolpyruvate carboxylase activity of 10-29 micromoles per milligram of chlorophyll per hour). Exposures of leaves of each species to 14CO2 (for 8 seconds) in the light resulted in 3-phosphoglycerate and sugar phosphates being the predominant initial 14C products (77-84%), with ≤4% of the 14C-label in malate plus aspartate. These results indicate that in the C3-C4 intermediate P. hysterophorus, the reduction in leaf photorespiration cannot be attributed to C4 photosynthesis. 相似文献
14.
Compensation point and isotopic characteristics of c(3)/c(4) intermediates and hybrids in panicum 总被引:1,自引:0,他引:1
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Leaf CO2 compensation points and stable hydrogen, oxygen and carbon isotope ratios were determined for Panicum species including C3/C4 intermediate photosynthesis plants, hybrids between C3/C4 intermediates and C3 plants, C3 and C4 plants in the Panicum genus as well as several other C3 and C4 plants. C3 plants had the highest compensation points, followed by hybrids, C3/C4 intermediates, and C4 plants. δ13C values of cellulose nitrate and saponifiable lipids from C4 plants were about 10‰ higher than those observed for cellulose nitrate and saponifiable lipids of C3/C4 intermediates, hybrids, and C3 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 C3/C4 intermediates, hybrids, C3, and C4 plants is due to fractionations occurring during biochemical reactions specific to leaf carbohydrate metabolism. 相似文献
15.
Thermal regulation of phosphoenolpyruvate carboxylase and ribulose-1,5-bisphosphate carboxylase in c(3) and c(4) plants native to hot and temperate climates 总被引:7,自引:6,他引:1
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Exposure of leaf sections from 2-week-old seedlings of sorghum (Sorghum bicolor L.) (C4 plant), corn (Zea mays L.) (C4), peanut (Arachis hypogaea L.) (C3 plant), and soybean (Glycine max L.) (C3) to 40 or 45°C for up to 4 hours resulted in significant increases in the levels of 102 kilodalton (C4), 52 kilodalton (C3 and C4), and 15 kilodalton (C3 and C4) 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
16.
Phosphate Translocator of Mesophyll and Bundle Sheath Chloroplasts of a C(4) Plant, Panicum miliaceum L. : Identification and Kinetic Characterization 总被引:1,自引:1,他引:0
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The phosphate translocator was identified in the envelope membranes of both mesophyll and bundle sheath chloroplasts of Panicum miliaceum L. by labeling with [1,2-3H]1,2-(2,2′ -disulfo-4,4′ -diisothiocyano)diphenylethane ([3H]H2DIDS) and by using SDS-PAGE. Assay of 32Pi uptake by the chloroplasts showed that the phosphate translocators of both types of chloroplasts have a higher affinity for phosphoenolpyruvate than the C3 counterpart and can be regarded as C4 types. 相似文献
17.
Inheritance of c(4) enzymes associated with carbon fixation in flaveria species 总被引:1,自引:0,他引:1
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Activities and subunit levels of three C4 enzymes were determined for F1 hybrids between C4 and C3-C4Flaveria species. For phosphoenolpyruvate carboxylase and pyruvate orthophosphate, dikinase, enzyme amounts in the hybrids were close to the mid-parent means. However, activity and subunit levels of NADP-malic enzyme were approximately one-half the mid-parent mean. 相似文献
18.
Sulfur assimilation in c(4) plants: intercellular compartmentation of adenosine 5'-triphosphate sulfurylase in crabgrass leaves
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The activity of adenosine 5′ triphosphate sulfurylase was determined in crabgrass mesophyll cells, bundle sheath strands, and whole leaf extracts. The enzyme was assayed by following molybdate-dependent pyrophosphate release from ATP, 35SO42− incorporation into adenosine 5′ phosphosulfate, and ATP synthesis dependent upon adenosine 5′ phosphosulfate and inorganic pyrophosphate. With all assays, greater than 90% of the activity was found in extracts from bundle sheath strands. The activities in whole leaf extracts were consistently intermediate between the activities of mesophyll and bundle sheath extracts and extract-mixing experiments gave no indication of enzyme activation or inhibition in vitro. Whole leaf activities were several hundred-fold less than concurrent measurements of ribulose 1,5-bisphosphate and phosphoenolpyruvate carboxylase activities, which is interpreted as being consistent with the relative amounts of elemental carbon and sulfur found in higher plants. A hypothesis is presented for the intercellular compartmentation of sulfur assimilation in relationship to NO3− and CO2 assimilation in leaves of C4 plants. 相似文献
19.
Carbon isotope ratios demonstrate carbon flux from c(4) host to c(3) parasite 总被引:2,自引:0,他引:2
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Carbon isotope ratios of mature leaves from the C3 angiosperm root hemiparasites Striga hermonthica (Del.) Benth (−26.7‰) and S. asiatica (L.) Kuntze (−25.6‰) were more negative than their C4 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 C3-C3 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 δ13C-values of 5 to 6‰ suggests that even in mature, photosynthetically active plants, there is substantial input of carbon from the C4 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
20.
The potential for C4 photosynthesis was investigated in five C3-C4 intermediate species, one C3 species, and one C4 species in the genus Flaveria, using 14CO2 pulse-12CO2 chase techniques and quantum-yield measurements. All five intermediate species were capable of incorporating 14CO2 into the C4 acids malate and aspartate, following an 8-s pulse. The proportion of 14C label in these C4 products ranged from 50–55% to 20–26% in the C3-C4 intermediates F. floridana Johnston and F. linearis Lag. respectively. All of the intermediate species incorporated as much, or more, 14CO2 into aspartate as into malate. Generally, about 5–15% of the initial label in these species appeared as other organic acids. There was variation in the capacity for C4 photosynthesis among the intermediate species based on the apparent rate of conversion of 14C label from the C4 cycle to the C3 cycle. In intermediate species such as F. pubescens Rydb., F. ramosissima Klatt., and F. floridana we observed a substantial decrease in label of C4-cycle products and an increase in percentage label in C3-cycle products during chase periods with 12CO2, although the rate of change was slower than in the C4 species, F. palmeri. In these C3-C4 intermediates both sucrose and fumarate were predominant products after a 20-min chase period. In the C3-C4 intermediates, F. anomala Robinson and f. linearis we observed no significant decrease in the label of C4-cycle products during a 3-min chase period and a slow turnover during a 20-min chase, indicating a lower level of functional integration between the C4 and C3 cycles in these species, relative to the other intermediates. Although F. cronquistii Powell was previously identified as a C3 species, 7–18% of the initial label was in malate+aspartate. However, only 40–50% of this label was in the C-4 position, indicating C4-acid formation as secondary products of photosynthesis in F. cronquistii. In 21% O2, the absorbed quantum yields for CO2 uptake (in mol CO2·[mol quanta]-1) averaged 0.053 in F. cronquistii (C3), 0.051 in F. trinervia (Spreng.) Mohr (C4), 0.052 in F. ramosissima (C3-C4), 0.051 in F. anomala (C3-C4), 0.050 in F. linearis (C3-C4), 0.046 in F. floridana (C3-C4), and 0.044 in F. pubescens (C3-C4). In 2% O2 an enhancement of the quantum yield was observed in all of the C3-C4 intermediate species, ranging from 21% in F. ramosissima to 43% in F. pubescens. In all intermediates the quantum yields in 2% O2 were intermediate in value to the C3 and C4 species, indicating a co-function of the C3 and C4 cycles in CO2 assimilation. The low quantum-yield values for F. pubescens and F. floridana in 21% O2 presumably reflect an ineffcient transfer of carbon from the C4 to the C3 cycle. The response of the quantum yield to four increasing O2 concentrations (2–35%) showed lower levels of O2 inhibition in the C3-C4 intermediate F. ramosissima, relative to the C3 species. This indicates that the co-function of the C3 and C4 cycles in this intermediate species leads to an increased CO2 concentration at the site of ribulose-1,5-bisphosphate carboxylase/oxygenase and a concomitant decrease in the competitive inhibition by O2.Abbreviations PEP
phosphoenolpyruvate
- PGA
3-phosphoglycerate
- RuBP
ribulose-1,5-bisphosphate 相似文献