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1.
The effect of 3,3-dichloro-2-(dihydroxyphosphinoylmethyl)-propenoate (DCDP), an analog of phosphoe nolpyruvate (PEP), on PEP carboxylase activity in crude leaf extracts and on photosynthesis of excised leaves was examined. DCDP is an effective inhibitor of PEP carboxylase from Zea mays or Panicum miliaceum; 50% inhibition was obtained at 70 or 350 micromolar, respectively, in the presence of 1 millimolar PEP and 1 millimolar HCO 3−. When fed to leaf sections via the transpiration stream, DCDP at 1 millimolar strongly inhibited photosynthesis in C 4 species (79-98% inhibition for a range of seven C 4 species), but only moderately in C 3 species (12-46% for four C 3 species), suggesting different mechanisms of inhibition for each photosynthetic type. The response of P. miliaceum (C 4) net photosynthesis to intercellular pCO 2 showed that carboxylation efficiency, as well as the CO 2 saturated rate, are lowered in the presence of DCDP and supported the view that carboxylation efficiency in C 4 species is directly related to PEP carboxylase activity. A fivefold increase in intercellular pCO 2 over that occurring in P. miliaceum under normal photosynthesis conditions only increased net photosynthesis rate in the presence of 1 millimolar DCDP from zero to about 5% of the maximal uninhibited rate. Therefore, it seems unlikely that direct fixation of atmospheric CO 2 by the bundle sheath cells makes any significant contribution to photosynthetic CO 2 assimilation in C 4 species. The results support the concept that C 4-selective herbicides may be developed based on inhibitors of C 4 pathway reactions. 相似文献
2.
Hybrids have been made between species of Flaveria exhibiting varying levels of C 4 photosynthesis. The degree of C 4 photosynthesis expressed in four interspecific hybrids ( Flaveria trinervia [C 4] × F. linearis [C 3-C 4], F. brownii [C 4-like] × F. linearis, and two three-species hybrids from F. trinervia × [ F. brownii × F. linearis]) was estimated by inhibiting phosphoe nolpyruvate carboxylase in vivo with 3,3-dichloro-2-dihydroxyphosphinoylmethyl-2-propenoate (DCDP). The inhibitor was fed to detached leaves at a concentration of 4 m m, and apparent photosynthesis was measured at atmospheric levels of CO 2 and at 20 and 210 mL L −1 of O 2. Photosynthesis at 210 mL L −1 of O 2 was inhibited 32% by DCDP in F. linearis, by 60% in F. brownii, and by 87% in F. trinervia. Inhibition in the hybrids ranged from 38 to 52%. The inhibition of photosynthesis by 210 mL L −1 of O 2 was increased when DCDP was used, except in the C 4 species, F. trinervia, in which photosynthesis was insensitive to O 2. Except for F. trinervia, control plants with less O 2 sensitivity (more C 4-like) exhibited a progressively greater change in O 2 inhibition of photosynthesis when treated with DCDP. This increased O 2 inhibition probably resulted from decreased CO 2 concentrations in bundle sheath cells due to inhibition of phosphoe nolpyruvate carboxylase. The inhibition of photosynthesis by DCDP is concluded to underestimate the degree of C 4 photosynthesis in the interspecific hybrids because increased direct assimilation of atmospheric CO 2 by ribulose bisphosphate carboxylase may compensate for inhibition of phosphoe nolpyruvate carboxylase. 相似文献
3.
Diffusion of inorganic carbon into isolated bundle sheath cells from a variety of C 4 species was characterized by coupling inward diffusion of CO 2 to photosynthetic carbon assimilation. The average permeability coefficient for CO 2 ( PCO2) for five representatives from the three decarboxylation types was approximately 20 micromoles per minute per milligram chlorophyll per millimolar, on a leaf chlorophyll basis. The average value for the NAD-ME species Panicum miliaceum (10 determinations) was 26 with a standard deviation of 6 micromoles per minute per milligram chlorophyll per millimolar, on a leaf chlorophyll basis. A PCO2 of at least 500 micromoles per minute per milligram chlorophyll per millimolar was determined for cells isolated from the C 3 plant Xanthium strumarium. It is concluded that bundle sheath cells are one to two orders of magnitude less permeable to CO 2 than C 3 photosynthetic cells. These data also suggest that CO 2 diffusion in bundle sheath cells may be made up of two components, one involving an apoplastic path and the other a symplastic (plasmodesmatal) path, each contributing approximately equally. 相似文献
4.
The activities of certain enzymes related to the carbon assimilation pathway in whole leaves, mesophyll cell extracts, and bundle sheath extracts of the C 4 plant Panicum miliaceum have been measured and compared on a chlorophyll basis. Enzymes of the C 4 dicarboxylic acid pathway—phosphoenolpyruvate carboxylase and NADP-malic dehydrogenase—were localized in mesophyll cells. Carbonic anhydrase was also localized in mesophyll cell extracts. Ribose 5-phosphate isomerase, ribulose 5-phosphate kinase, and ribulose diphosphate carboxylase—enzymes of the reductive pentose phosphate pathway—were predominantly localized in bundle sheath extracts. High activities of aspartate and alanine transaminases and glyceraldehyde-3-P dehydrogenase were found about equally distributed between the photosynthetic cell types. P. miliaceum had low malic enzyme activity in both mesophyll and bundle sheath extracts. 相似文献
5.
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 CO 2 compensation concentration (20-25 microliters per liter at 30°C and 21% O 2) and by a reduced sensitivity of net photosynthesis to 21% O 2. In contrast, the related C 3 species P. incanum and P. argentatum (guayule) lack Kranz anatomy, have higher CO 2 compensation concentrations (about 55 microliters per liter), and show a greater inhibition of photosynthesis by 21% O 2. Furthermore, in P. hysterophorus the CO 2 compensation concentration is relatively less sensitive to changes in O 2 concentrations and shows a biphasic response to changing O 2, with a transition point at about 11% O 2. Based on these results, P. hysterophorus is classified as a C 3-C 4 intermediate. The activities of diagnostic enzymes of C 4 photosynthesis in P. hysterophorus were very low, comparable to those observed in the C 3 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 14CO 2 (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 C 3-C 4 intermediate P. hysterophorus, the reduction in leaf photorespiration cannot be attributed to C 4 photosynthesis. 相似文献
6.
A theoretical model of the composition of the inorganic carbon pool generated in C 4 leaves during steady-state photosynthesis was derived. This model gives the concentrations of CO 2 and O 2 in the bundle sheath cells for any given net photosynthesis rate and inorganic carbon pool size. The model predicts a bundle sheath CO 2 concentration of 70 micromolar during steady state photosynthesis in a typical C 4 plant, and that about 13% of the inorganic carbon generated in bundle sheath cells would leak back to the mesophyll cells, predominantly as CO 2. Under these circumstances the flux of carbon through the C 4 acid cycle would have to exceed the net rate of CO 2 assimilation by 15.5%. With the calculated O 2 concentration of 0.44 millimolar, the potential photorespiratory CO 2 loss in bundle sheath cells would be about 3% of CO 2 assimilation. Among the factors having a critical influence on the above values are the permeability of bundle sheath chloroplasts to HCO 3−, the activity of carbonic anhydrase within these chloroplasts, the assumed stromal volume, and the permeability coefficients for CO 2 and O 2 diffusion across the interface between bundle sheath and mesophyll cells. The model suggests that as the net photosynthesis rate changes in C 4 plants, the level and distribution of the components of the inorganic carbon pool change in such a way that C 4 acid overcycling is maintained in an approximately constant ratio with respect to the net photosynthesis rate. 相似文献
7.
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
8.
Bundle sheath cells were enzymatically isolated from representatives of three groups of C 4 plants: Zea mays (NADP malic enzyme type), Panicum miliaceum (NAD malic enzyme type), and Panicum maximum (phosphoenolpyruvate (PEP) carboxykinase type). Cellular organelles from bundle sheath homogenates were partially resolved by differential centrifugation and on isopycnic sucrose density gradients in order to study compartmentation of photosynthetic enzymes. A 48-h-dark pretreatment of the leaves allowed the isolation of relatively intact chloroplasts. Enzymes that decarboxylate C 4 acids and furnish CO 2 to the Calvin cycle are localized as follows: NADP malic enzyme, chloroplastic in Z. mays; NAD malic enzyme, mitochondrial in all three species; PEP carboxykinase, chloroplastic in P. maximum. The activity of NAD malic enzyme in the three species was in the order of P. miliaceum > P. maximum > Z. mays. There were high levels of aspartate and alanine aminotransferases in bundle sheath extracts of P. miliaceum and P. maximum and substantial activity in Z. mays. In all three species, aspartate aminotransferase was mitochondrial whereas alanine aminotransferase was cytoplasmic. Based on the activity and localization of certain enzymes, the concept for aspartate and malate as transport metabolites from mesophyll to bundle sheath cells in C 4 species of the three C 4 groups is discussed. 相似文献
9.
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
10.
Bundle sheath chloroplasts have been isolated from Zea mays leaves by a procedure involving enzymic digestion of mechanically prepared strands of bundle sheath cells followed by gentle breakage and filtration. The resulting crude chloroplast preparation was enriched by Percoll density layer centrifugation to yield intact chloroplasts (about 20 micrograms chlorophyll per 10-gram leaf tissue) with high metabolic activities. Based on activities of marker enzymes in the chloroplast and bundle sheath cell extracts, the chloroplasts were essentially free of contamination by other organelles and cytoplasmic material, and were generally about 70% intact. Chlorophyll a/b ratios were high (about 10). With appropriate substrates these chloroplasts displayed high rates of malate decarboxylation, measured as pyruvate formation, and CO 2 assimilation (maximum rates approximately 5 and 3 micromoles per minute per milligram chlorophyll, respectively). These activities were light dependent, linear for at least 20 minutes at 30°C, and displayed highest rates at pH 8.0. High metabolic rates were dependent on addition of an exogenous source of carbon to the photosynthetic carbon reduction cycle (3-phosphoglycerate or dihydroxyacetone phosphate) and a nucleotide (ATP, ADP, or AMP), as well as aspartate. Generally, neither malate decarboxylation nor CO 2 assimilation occurred substantially in the absence of the other activity indicating a close relationship between these processes. Presumably, NADPH required for the photosynthetic carbon reduction cycle is largely supplied during the decarboxylation of malate by NADP-malic enzyme. The results are discussed in relation to the role of bundle sheath chloroplasts in C 4 photosynthesis by species of the NADP-malic enzyme type. 相似文献
11.
Mesophyll cells and bundle sheath strands were isolated from Cyperus rotundus L. leaf sections infiltrated with a mixture of cellulase and pectinase followed by a gentle mortar and pestle grind. The leaf suspension was filtered through a filter assembly and mesophyll cells and bundle sheath strands were collected on 20-μm and 80-μm nylon nets, respectively. For the isolation of leaf epidermal strips longer leaf cross sections were incubated with the enzymes and gently ground as above. Loosely attached epidermal strips were peeled off with forceps. The upper epidermis, which lacks stomata, could be clearly distinguished from the lower epidermis which contains stomata. Microscopic evidence for identification and assessment of purity is provided for each isolated tissue.Enzymes related to the C 4-dicarboxylic acid cycle such as phosphoenolpyruvate carboxylase, malate dehydrogenase (NADP +), pyruvate, P i dikinase were found to be localized, ≥98%, in mesophyll cells. Enzymes related to operating the reductive pentose phosphate cycle such as RuDP carboxylase, phosphoribulose kinase, and malic enzyme are distributed, ≥99%, in bundle sheath strands. Other photosynthetic enzymes such as aspartate aminotransferase, pyrophosphatase, adenylate kinase, and glyceraldehyde 3- P dehydrogenase (NADP +) are quite active in both mesophyll and bundle sheath tissues.Enzymes involved in photorespiration such as RuDP oxygenase, catalase, glycolate oxidase, hydroxypyruvate reductase (NAD +), and phosphoglycolate phosphatase are preferentially localized, ≥84%, in bundle sheath strands.Nitrate and nitrite reductase can be found only in mesophyll cells, while glutamate dehydrogenase is present, ≥96%, in bundle sheath strands.Starch- and sucrose-synthesizing enzymes are about equally distributed between the mesophyll and bundle sheath tissues, except that the less active phosphorylase was found mainly in bundle sheath strands. Fructose-1,6-diP aldolase, which is a key enzyme in photosynthesis and glycolysis leading to sucrose and starch synthesis, is localized, ≥90%, in bundle sheath strands. The glycolytic enzymes, phosphoglyceromutase and enolase, have the highest activity in mesophyll cells, while the mitochondrial enzyme, cytochrome c oxidase, is more active in bundle sheath strands.The distribution of total nutsedge leaf chlorophyll, protein, and PEP carboxylase activity, using the resolved leaf components, is presented. 14CO 2 Fixation experiments with the intact nutsedge leaves and isolated mesophyll and bundle sheath tissues show that complete C 4 photosynthesis is compartmentalized into mesophyll CO 2 fixation via PEP carboxylase and bundle sheath CO 2 fixation via RuDP carboxylase. These results were used to support the proposed pathway of carbon assimilation in C 4-dicarboxylic acid photosynthesis and to discuss the individual metabolic characteristics of intact mesophyll cells, bundle sheath cells, and epidermal tissues. 相似文献
12.
A mechanical isolation procedure was developed to study the respiratory properties of mitochondria from the mesophyll and bundle sheath tissue of Panicum miliaceum, a NAD-malic enzyme C 4 plant. A mesophyll fraction and a bundle sheath fraction were obtained from young leaves by differential mechanical treatment. The purity of both fractions was about 80%, based on analysis of the cross-contamination of ribulose bisphosphate carboxylase activity and phosphoenolpyruvate carboxylase activity. Mitochondria were isolated from the two fractions by differential centrifugation and Percoll density gradient centrifugation. The enrichment of mitochondria relative to chloroplast material was about 75-fold in both preparations. Both types of mitochondria oxidized NADH and succinate with respiratory control. Malate oxidation in mesophyll mitochondria was sensitive to KCN and showed good respiratory control. In bundle sheath mitochondria, malate oxidation was largely insensitive to KCN and showed no respiratory control. The oxidation was strongly inhibited by salicylhydroxamic acid, showing that the alternative oxidase was involved. The bundle sheath mitochondria of this type of C4 species contribute to C4 photosynthesis through decarboxylation of malate. Malate oxidation linked to an uncoupled, alternative pathway may allow decarboxylation to proceed without the restraints which might occur via coupled electron flow through the cytochrome chain. 相似文献
13.
A procedure is described for isolating and purifying mesophyll protoplasts and bundle sheath protoplasts of the C 4 plant Panicum miliaceum. Following enzymic digestion of leaf tissue, mesophyll protoplasts and bundle sheath protoplasts are released and purified by density centrifugation. The lower density of mesophyll protoplasts allowed rapid separation of the two protoplast types. Evidence for separation of mesophyll protoplasts and bundle sheath protoplasts (up to 95% purity) is provided from light microscopy (based on size difference in both chloroplasts and protoplasts), levels of marker enzymes in the preparations ( i.e. pyruvate, Pi dikinase and phosphoenolpyruvate carboxylase for mesophyll and ribulose-1,5-bisphosphate carboxylase for bundle sheath), and differences in substrate-dependent O 2 evolution by chloroplasts isolated from protoplasts. 相似文献
14.
We sought to characterize the inorganic carbon pool (CO 2 plus HCO 3−) formed in the leaves of C 4 plants when C 4 acids derived from CO 2 assimilation in mesophyll cells are decarboxylated in bundle sheath cells. The size and kinetics of labeling of this pool was determined in six species representative of the three metabolic subgroups of C 4 plants. The kinetics of labeling of the inorganic carbon pool of leaves photosynthesizing under steady state conditions in 14CO 2 closely paralleled those for the C-4 carboxyl of C 4 acids for all species tested. The inorganic carbon pool size, determined from its 14C content at radioactivity saturation, ranged between 15 and 97 nanomoles per milligram of leaf chlorophyll, giving estimated concentrations in bundle sheath cells of between 160 and 990 micromolar. The size of the pool decreased, together with photosynthesis, as light was reduced from 900 to 95 microeinsteins per square meter per second or as external CO 2 was reduced from 400 to 98 microliters per liter. A model is developed which suggests that the inorganic carbon pool existing in the bundle sheath cells of C 4 plants during steady state photosynthesis will comprise largely of CO 2; that is, CO 2 will only partially equlibrate with bicarbonate. This predominance of CO 2 is believed to be vital for the proper functioning of the C 4 pathway. 相似文献
15.
Characteristics of C 4 photosynthesis were examined in young, mid-age, and mature leaves of Flaveria trinervia (an NADP-malic enzyme-type C 4 dicot). The turnover of [4- 14C] (malate plus aspartate) following a pulse with 14CO 2 was similar in leaves of different ages (apparent half-time of 18-25 seconds). However, the rate of 14CO 2 incorporation in mid-age leaves was about 1.5-fold higher than in young leaves, and about 2.5-fold higher than in mature leaves. The rate of 14CO 2 fixation was proportional to the total active pool of malate plus aspartate but was not correlated with the total photosynthetically derived inorganic carbon pool. The leaf's ability to concentrate inorganic carbon photosynthetically declined during leaf expansion, from 29 down to 7 nanomoles per milligram chlorophyll. Similarly, the active aspartate pool also declined during leaf expansion, from about 123 down to 20 nanomoles per milligram chlorophyll. Enhanced metabolism of aspartate to CO 2 and pyruvate in young leaves is suggested to facilitate the maintenance of high CO 2 levels in bundle sheath cells which are thought to have a higher conductance to CO 2. 相似文献
16.
Intercellular distribution of enzymes involved in amino nitrogen synthesis was studied in leaves of species representing three C 4 groups, i.e. Sorghum bicolor, Zea mays, Digitaria sanguinalis (NADP malic enzyme type); Panicum miliaceum (NAD malic enzyme type); and Panicum maximum (phosphoenolpyruvate carboxykinase type). Nitrate reductase, nitrite reductase, glutamine synthetase, and glutamate synthase were predominantly localized in mesophyll cells of all the species, except in P. maximum where nitrite reductase had similar activity on a chlorophyll basis, in both mesophyll and bundle sheath cells. NADH-glutamate dehydrogenase was concentrated in the bundle sheath cells, while NADPH-glutamate dehydrogenase was localized in both mesophyll and bundle sheath cells. The activities of nitrate-assimilating enzymes, except for nitrate reductase, were high enough to account for the proposed in vivo rates of nitrate assimilation. 相似文献
17.
The aim of this work was to investigate the fate of phosphoenolpyruvate (PEP) produced by decarboxylation of oxaloacetate during photosynthesis in the bundle sheaths of leaves of the PEP-carboxykinase C 4 grass Spartina anglica Hubb. Mesophyll protoplasts and bundle sheath cells were separated enzymically and used to investigate activities and distributions of putative enzymes of the C 4 cycle and the photosynthetic carbon metabolism of bundle sheath cells. The results indicate that neither conversion of PEP to pyruvate nor its conversion to 3-phosphoglycerate can account for all of the carbon flux through the C 4 cycle during photosynthesis. It is likely, therefore, either that PEP moves directly from bundle sheath to mesophyll or that more than one pathway of regeneration of PEP is involved in the C 4 cycle in this plant.Abbreviations Chl
chlorophyll
- PEP
phosphoenolpyruvate
- Pi
phosphate
- RuBP
ribulose-1,5-bisphosphate 相似文献
18.
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]H 2DIDS) 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 phospho enolpyruvate than the C 3 counterpart and can be regarded as C 4 types. 相似文献
19.
Mature leaves of Cyperus rotundus, Cyperus polystachyos, Digitaria decumbens, and Digitaria sanguinalis were separated, using pectinase and cellulase, into pure preparations of mesophyll cells and bundle sheath strands. Assays on these distinct leaf cell types show a clear compartmentation of phosphoenolpyruvate carboxylase, >98%, into mesophyll cells and of ribulose-1, 5-diphosphate carboxylase and malic enzyme, >98%, into the bundle sheath strands. The results clearly establish that the major CO 2 uptake in mesophyll cells is via a β-carboxylation and that both a decarboxylation and a carboxylation reaction occurs in the bundle sheath strands of plants using C 4-dicarboxylic acid photosynthesis. 相似文献
20.
Two-dimensional electrophoresis was performed on proteins of bundle sheath and mesophyll cells isolated from the C 4 grass Digitaria sanguinalis (L.) Scop. Two-dimensional maps of these proteins were constructed and ribulose-1,5-biphosphate carboxylase and phosphoenolpyruvate carboxylase were identified. Of the total number of proteins found in both cell types, 36% were found only in bundle sheath cells, 17% only in mesophyll cells, and 47% in both cell types. By comparison, the distributions of 48 enzymes assayed in these cell types were 35%, 21%, and 44%, respectively. Protein patterns were also compared with C4 plants exhibiting different decarboxylation pathways and, in both bundle sheath and mesophyll cells, proteins were found which were unique to each species. Bundle sheath proteins of one C4 species were found to be more like bundle sheath proteins of another C4 species than like mesophyll proteins of the same species. 相似文献
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