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1.
The effects of phosphoenolpyruvate (PEP), inorganic phosphate (Pi), and ATP on 3-phosphoglycerate (PGA)-dependent O 2 evolution by chloroplasts of Digitaria sanguinalis (L.) Scop. (crabgrass) were evaluated relative to possible mechanisms of PEP transport by the C 4 mesophyll chloroplast. Crude and Percoll purified chloroplast preparations exhibited rates of PGA-dependent O 2 evolution in the range of 90 to 135 micromoles O 2 per milligram chlorophyll per hour, and up to 180 micromoles O 2 per milligram chlorophyll per hour at optimal Pi concentrations (approximately 0.2 millimolar at 9 millimolar PGA). Higher concentrations of Pi were inhibitory. PEP inhibited O 2 evolution (up to 70%) in both chloroplast preparations when the PEP to PGA ratio was high ( i.e. 9 millimolar PEP to 0.36 millimolar PGA). Usually no inhibition was seen when the PEP to PGA ratio was less than 2. PEP acted as a competitive inhibitor and, at a concentration of 9 millimolar, increased the apparent K m (PGA) from 0.15 to 0.53 millimolar in Percoll purified chloroplasts. A low concentration of PGA and high ratio of PEP to PGA, which are considered unphysiological, were required to detect any inhibition of O 2 evolution by PEP. Similar results were obtained from crude versus Percoll purified preparations. Neither the addition of Pi nor ATP could overcome PEP inhibition. As PEP inhibition was competitive with respect to PGA concentration, and as addition of ATP or Pi could not prevent PEP inhibition of PGA-dependent O 2 evolution, the inhibition was not due to PEP exchange of adenylates or Pi out of the chloroplast. Analysis of the effect of Pi and PEP, separately and in combination, on PGA-dependent O 2 evolution suggests interactions between PEP, Pi, and PGA on the same translocator in the C 4 mesophyll chloroplast. C 3 spinach chloroplasts were also found to be sensitive to PEP, but to a lesser extent than crabgrass chloroplasts. The apparent K i values (PEP) were 3 and 21 millimolar for crabgrass and spinach, respectively. 相似文献
2.
Light-enhanced active pyruvate uptake into mesophyll chloroplastsof C 4 plants was reported to be mimicked by either of the twotypes of cation jump: H +-jump in maize and phylogenically relatedspecies (H +-type) and Na +-jump in all the other C 4 species tested(Na +-type) [Aoki, N., Ohnishi, J. and Kanai, R. (1992) PlantCell Physiol. 33: 805]. In this study, medium and stromal pH was monitored in the suspensionof C 4 mesophyll chloroplasts. Medium alkalization lasting for5 to 10 seconds after pyruvate addition was detected by a pHelectrode and observed only in the light and only in mesophyllchloroplasts from H +-type species, Zea mays L. and Coix lacryma-jobiL., but not in those from Na +-type species Panicum miliaceumL., Setaria italica (L.) Beauv. and Panicum maximum Jacq. Theinitial rate of H + consumption showed good correlation with[ 14C]pyruvate uptake measured by silicone oil filtering centrifugation,both being inhibited by N-ethylmaleimide and 7-chloro-4-nitrobenzo-2-oxa-l,3-diazole to the same degree. The ratio of the rate of H + uptaketo that of pyruvate uptake was always about 1. Pyruvate-inducedacidification of the stroma was observed in maize mesophyllchloroplasts. These results show one to one cotransport of H +and pyruvate anion into mesophyll chloroplasts of H +-type C 4species in the light. (Received January 5, 1994; Accepted May 6, 1994) 相似文献
3.
Chloroplast envelopes were isolated from chloroplasts purifiedfrom Spinacea oleracea L. (C 3), Panicum miliaceum L. (NAD-malicenzyme-type C 1), Digitaria sanguinalis (L.) Scop. (NADP-malicenzyme-type C 4), Kalanchoe daigremontiana Hamet et Perrier (constitutiveCAM), and from Mesembryanthemum crystallinum L. (inducible CAM)performing either C 3 photosynthesis or Crassulacean acid metabolism(CAM). For each species, methods were developed to isolate chloroplastenvelopes free of thylakoid contamination. The polypeptidesof ribulose bisphosphate (RuBP) carboxylase which has been consistentlyreported in envelope preparations of spinach were not foundin envelope preparations of C 4 mesophyll chloroplasts. Silverstaining of envelope polypeptides resolved electrophoreticallyon sodium dodecylsulfate polyacrylamide gradient slab gels produceda more complex profile than did Coomassie staining which haspreviously been used with C 3 envelope preparations, even thoughsilver reacted poorly with polypeptides corresponding to thesubunits of RuBP carboxylase. All of the plants examined possesseda major polypeptide of 27 to 29 kilodaltons (kD) which was previouslysuggested to be the phosphate translocator in spinach. WithC 3 M. crystallinum, the 29 kD polypeptide stained most intensely.After induction of CAM, a 32 kD polypeptide also stained intensely,giving a profile similar to that obtained with the constitutiveCAM species. A 32 kD polypeptide was also prominent in C 4 envelopepreparations, suggesting that a 32 kD polypeptide may be a translocatorprotein which is required in Crassulacean acid metabolism andC4 photosynthesis, but not in C 3 photosynthesis. (Received April 25, 1983; Accepted July 9, 1983) 相似文献
4.
To study possible changes in the transport metabolites betweenchloroplasts and cytoplasm during CAM induction of Mesembryanthemumcrystallinum, we compared substrate specificity of P1 1 translocator(s)in isolated chloroplasts from the C 3 and CAM-induced plants.The [ 14C]glu-cose 6-phosphate (G6P) transport activity was significantonly in the chloroplasts of CAM-mode plants and not detectablein those of C 3-mode, while a similar high rate of [ 32P]P i uptakewas observed with both types of chloroplasts. Kinetic analysisof G6P uptake in the CAM chloroplasts showed a high V max [10.6µmol (mg Chl) 1 h 1] and a comparatively lowK m value (0.41 mM); the latter was similar to K i values of P i,3-phosphoglycerate and phospho- enolpyruvate, 0.30, 0.34 and0.47 mM, respectively. On the other hand, [32P]Pi uptake inthe CAM chloroplasts was inhibited competitively by G6P witha K i value (8.4 mM) 20-fold higher than the K m value for G6Puptake, while that in C 3 chloroplasts was not inhibited at all.These results suggest that a new G6P/P i, counterexchange mechanismis induced in the chloroplast envelope of CAM-induced M. crystallinumin addition to the ordinary type of P, translocator, that cannottransport G6P, already present in the C 3-type chloroplasts. (Received March 17, 1997; Accepted May 10, 1997) 相似文献
5.
The kinetic properties of the phosphate translocator from maize ( Zea mays L.) mesophyll chloroplasts have been determined. We have used a double silicone-oil-layer centrifugation system in order to obtain true initial uptake rates in forward-reaction experiments. In addition, it was possible to perform back-exchange experiments and to study the effects of illumination and of preloading the chloroplasts with different substrates on transport. It is shown that the phosphate translocator from mesophyll chloroplasts of maize, a C 4 plant, transports inorganic phosphate and phosphorylated C 3 compounds in which the phosphate group is linked to the C 3 atom (e.g. 3-phosphoglycerate and triose phosphate). The affinities of the transported metabolites towards the translocator protein are about one order of magnitude higher than in mesophyll chloroplasts from the C 3 plant, spinach. In contrast to the phosphate translocator from C 3-mesophyll chloroplasts, that of C 4-mesophyll chloroplasts catalyzes in addition the transport of C 3 compounds where the phosphate group is attached to the C 2 atom (e.g. 2-phosphoglycerate, phosphoenolpyruvate). The phosphate translocator from both chloroplast types is strongly inhibited by pyridoxal-5-phosphate (PLP), 2,4,6-trinitrobenzenesulfonic acid and 4,4-diisothiocyanostilbene-2,2-disulfonic acid (DIDS). In the case of the spinach translocator protein these inhibitors were shown to react with the same amino-acid residue at the substrate binding site, and one molecule of either DIDS or PLP is obviously required per substrate binding site for the inactivation of the translocation process. In the functionally active dimeric translocator protein only one substrate-binding site appears to be accessible at a particular time, indicating that the site might be exposed to each side of the membrane in turn. Using [ 3H]-H 2DIDS for the labelling of maize mesophyll envelopes the radioactivity was found to be associated with two polypeptides of about 29 and 30 kDa. Since Western-blot analysis showed that only the 30 kDa polypeptide reacted with an antiserum directed against the spinach phosphate translocator protein it is suggested that this polypeptide presumably represents the phosphate translocator from maize mesophyll chloroplasts.Abbreviations DIDS
4,4-diisothiocyanostilbene-2,2-disulfonic acid
- PEP
phosphoenolpyruvate
- 2-,3-PGA
2-,3-phosphoglycerate
- PLP
pyridoxal-5-phosphate
- SDS-PAGE
sodium dodecyl sulfate-polyacrylamide gel electrophoresis
- TNBS
2,4,6-trinitrobenzenesulfonic acid
- triose P
triose phosphate
This work was supported by the Deutsche Forschungsgemeinschaft 相似文献
6.
3-Phosphoglycerate (PGA)-dependent O 2 evolution by mesophyll chloroplasts of the C 4 plant, Digitaria sanguinalis L. Scop. (crabgrass), was inhibited by micromolar levels of 4,4′-diisothiocyano-2,2′-disulfonic acid stilbene (DIDS). As little as 1.8 micromolar DIDS added to the assay medium (containing 0.7 millimolar PGA) resulted in 80 to 100% inhibition of O 2 evolution. The extent of inhibition of O 2 evolution observed was dependent on various factors including: pH, concentration of DIDS to relative chlorophyll, concentration of PGA, and the time of addition of DIDS to the chloroplasts relative to addition of PGA. Preincubation of crabgrass chloroplasts with micromolar levels of DIDS, followed by washing to remove any nonirreversibly bound DIDS, inhibited PGA-dependent O2 evolution. Protection against this inhibition was afforded by preincubating the chloroplasts with various substrates before adding DIDS. For example, if the chloroplasts were first incubated with 8.3 millimolar PGA, phosphoenolpyruvate (PEP) or inorganic phosphate before adding 42 micromolar DIDS, the percentage of inhibition was decreased from 100% (without any substrate) to 0, 54, and 67%, respectively. 2-Phosphoglycerate caused a slight decrease in the inhibition (about 10%) and glucose-6-phosphate had no protective effect. If the chloroplasts were pretreated with DIDS initially, the inhibition could not be overcome by PGA, suggesting that DIDS acts as an irreversible inhibitor. Micromolar levels of DIDS also inhibited PGA dependent O2 evolution by isolated chloroplasts of the C3 plant barley. As with crabgrass, preincubation with PGA or inorganic phosphate resulted in a decrease in the DIDS inhibition, but PEP was very ineffective compared to the C4 chloroplasts. Oxalacetate-dependent O2 evolution and its stimulation by the uncoupler, NH4Cl, were unaffected by the addition of DIDS to crabgrass mesophyll chloroplasts. Furthermore, preincubation of the chloroplasts with DIDS (up to 65 micromolar) had no inhibitory effect on the extractable activity of NADP glyceraldehyde-3-P dehydrogenase and phosphoglycerate kinase. Inhibition by DIDS was interpreted to be at the substrate binding site of the phosphate translocator. The data further suggest that in C4 crabgrass chloroplasts, PEP is transported on a carrier which also transports PGA. 相似文献
7.
Enzymes of the C 4, C 3 pathway and photorespiration have beenanalyzed for P. hians and P. milioides, which have chlorenchymatousbundle sheath cells in the leaves. On whole leaf extracts thelevels of PEP carboxylase are relatively low compared to C 4species, RuDP carboxylase is typical of C 3 species, and enzymesof photorespiratory metabolism appear somewhat intermediatebetween C 3 and C 4. Substantial levels of PEP carboxylase, RuDPcarboxylase, and photorespiratory enzymes were found in bothmesophyll and bundle sheath cells. Low levels of C 4-acid decarboxylatingenzymes may limit the capacity for C 4 photosynthesis in P. hiansand P. milioides. The results on enzyme activity and distributionbetween mesophyll and bundle sheath cells are consistent withCO 2 fixation via C 3 pathway in these two species.
1 This research was supported by the College of Agriculturaland Life Sciences, University of Wisconsin, Madison; and bythe University of Wisconsin Research Committee with funds fromthe Wisconsin Alumni Research Foundation; and by the NationalScience Foundation Grant BMS 74-09611. (Received September 16, 1975; ) 相似文献
8.
Salsola arbusculiformis is identified as a C 3C 4intermediatespecies based on anatomical, biochemical and physiological characteristics.This is the first report of a naturally occurring intermediatespecies in the Chenopodiaceae, the family with the largest numberof C 4species amongst the dicots. In the genus Salsola, mostspecies have Salsoloid anatomy with Kranz type bundle sheathcells and C 4photosynthesis, while a few species have Sympegmoidanatomy and were found to have non-Kranz type bundle sheathcells and C 3photosynthesis. In the cylindrical leaves of C 4Salsolawith Salsoloid type anatomy, there is a continuous layer ofdistinct, chlorenchymatous Kranz type bundle sheath cells surroundedby a single layer of mesophyll cells; whereas species with Sympegmoidtype anatomy have an indistinct bundle sheath with few chloroplastsand multiple layers of chlorenchymatous mesophyll cells. However, S. arbusculiformis has intermediate anatomical features. Whileit has two-to-three layers of mesophyll cells, characteristicof Sympegmoid anatomy, it has distinctive, Kranz-like bundlesheath cells with numerous chloroplasts and mitochondria. Measurementsof its CO 2compensation point and CO 2response of photosynthesisshow S. arbusculiformis functions as an intermediate specieswith reduced levels of photorespiration. The primary means ofreducing photorespiration is suggested to be by refixing photorespiredCO 2in bundle sheath cells, since analysis of photosyntheticenzymes (activity and immunolocalization) and 14CO 2labellingof initial fixation products suggests minimal operation of aC 4cycle. Copyright 2001 Annals of Botany Company Immunolocalization, photosynthetic enzymes, C 3C 4intermediate, C 4-plants, leaf anatomy, Chenopodiaceae, Salsola arbusculiformis 相似文献
9.
The kinetic properties of phosphoenolpyruvate (PEP) carboxylasehave been studied among several Flaveria species: the C 3 species F. cronquistii, the C 3C 4 species F. pubescens and F.linearis, and the C 4 species F. trinervia. At either pH 7 or8, the maximum activities (in µmol.mg Chl 1.h 1)for F. pubescens and linearis (187513) were intermediateto those of the C 3 species (1219) and the C 4 species(2,1822,627). The response curves of velocity versusPEP concentration were hyperbolic for the C 3 and C 3C 4species at either pH 7 or 8 while they were sigmoidal for theC 4 species at pH 7 and hyperbolic at pH 8. The Km values forPEP determined from reciprocal plots were lowest in the C 3 species,and of intermediate value in the C 3C 4 species comparedto the K' values of the C 4 species determined from Hill plotsat either pH 7 or 8. Glucose-6-phosphate (G6P) decreased the Km values for PEP at both pH 7 and 8 in the C 3 and C 3C 4species. In the C 4 species, G6P decreased the K' values at pH8 but increased the K' values at pH 7. In all cases, G6P hadits effect by influencing the activity at limiting PEP concentrationswith little or no effect on the maximum activity. At pH 8 andlimiting concentrations of PEP the degree of stimulation ofthe activity by G6P was greatest in the C 4 species, intermediatein F. linearis, a C 3C 4 species, and lowest in the C 3species. In several respects, the PEP carboxylases of the C 3C 4Flaveria species have properties intermediate to those of theC 3 and C 4 species. (Received April 30, 1983; Accepted August 22, 1983) 相似文献
10.
The influence of varying light intensity and quality on thecarbon labelling patterns in Rumex vesicarius (a C 3 plant), Setaria italica (a malate-formingC 4 plant), and Amaranthus paniculatus(an aspartate-forming C 4 plant) was studied. In A. paniculatusand B. vesicarius blue light decreased the transfer of radioactivityto sugars and starch but in S. italica only slightly decreasedradioactivity in sugar phosphates, sucrose, and insolubles.Negligible transfer was observed from the C 4 acids to sugarphosphates, sucrose, and starch under dim blue-green and blue-yellowlights in S. italica and A. paniculatus. Blue light favouredthe formation of malate, aspartate, and alanine in all threeplants. The differential effect of blue and red light suggesteda variation in the mechanisms of C 4-photosynthesis in Setariaand Amaranthus. Leaves of S. italica and A. paniculatus were allowed to photosynthesizein 14CO 2 for 5 s and then the distribution of the labelled productsbetween the mesophyll and the bundle sheath cells was determinedduring subsequent photosynthesis in 12CO 2. Malate and aspartatewhich appeared initially in the mesophyll layer moved rapidlyinto the bundle sheath cells. Phosphoglyceric acid originatingin the bundle sheath moved swiftly to the mesophyll layer. Sugarphosphates were recovered from both the mesophyll and the bundlesheath cells. Most of the starch was found in the bundle sheathcells while sucrose and alanine were localized in the mesophyllcells. 相似文献
11.
Panicum hians and Panicum milioides were found to have characteristicsintermediate to those of C 3 and C 4 species with respect to CO 2compensation point, percentage inhibition of photosynthesisby O 2 at various O 2/CO 2 solubility ratios, and water use efficiency.C 4 species have a higher carboxylation efficiency than eitherthe intermediate or C 3 species. During photosynthesis, evenunder 2.5% O 2, C 4 species have a higher affinity for intercellularCO 2 ( Km 1.6 µM) apparently due to the initial carboxylationthrough PEP carboxylase. Under low O 2 the intermediate and C 3species had a similar affinity for intercellular CO 2 duringphotosynthesis ( Km 57 µM) consistent with carboxylationof atmospheric CO 2 through RuDP carboxylase. There were considerablevariation in photosynthesis/unit leaf area at saturating CO 2levels in the species examined which in part is due to differencesin RuDP carboxylase /unit leaf area. The highest rates of photosynthesis/unitleaf area under CO 2-saturating conditions were with the C 3 specieswhich had a correspondingly high level of RuDP carboxylase/unitleaf area. Possibilities for the greater efficiency of P. hiansand P. milioides in comparison to C 3 species in utilizing lowlevels of CO 2 in the presence of atmospheric O 2 are discussed.
1 This research was supported by the College of Agriculturaland Life Sciences, University of Wisconsin, Madison; and theUniversity of Wisconsin Research Committee with funds from theWisconsin Alumni Research Foundation. (Received June 25, 1977; ) 相似文献
12.
Light-dependent active uptake of pyruvate was reported in mesophyllchloroplasts of a C 4 plant, Panicum miliaceum [Ohnishi and Kanai(1987) Plant Cell Physiol. 28: 1]. The present study tried toclarify the energy source of this active uptake. Preilluminationof the mesophyll chloroplasts increased over tenfold their pyruvateuptake in the light and dark. This indicates that light itselfis not essential for the enhancement. The pyruvate uptake capacity(the initial uptake rate) of the mesophyll chloroplasts increasedon illumination and reached a steady-state level after a fewminutes; this rise was faster under higher light intensities.When the chloroplasts were returned to darkness, the uptakecapacity decayed with a half-life of about 1 min; this was independentof the light intensity of preillumination. Illumination of thechloroplasts also increased the stromal pH from about 7 to 8and the stromal ATP level from about 5 to 1525 nmol.(mg chl) 1. The change of the former during dark-to-lightand light-to-dark transitions occurred within 2 to 5 min, whilethe change of the latter took place much faster within 1 min.The steady-state levels of the pyruvate uptake capacity andstromal pH were saturated at a light intensity of 3 µE.m 2.s 1,while the ATP level increased with a further increase in thelight intensity. The former two parameters also showed similarsensitivity to the inhibition by carbonylcyanide- m-chlorophenylhydrazone,while a higher concentration of the inhibitor was needed toreduce the ATP level. Nitrite at 4 mM inhibited the light-dependentpyruvate uptake and stromal alkalization but had little effecton the stromal ATP level, while 2 mM arsenate decreased thestromal ATP without significant effects on pyruvate uptake andstromal pH. The good correlation of pyruvate uptake and stromalpH suggests that the active pyruvate uptake by the mesophyllchloroplasts is primarily driven by the pH gradient across theenvelope. (Received August 15, 1986; Accepted December 8, 1986) 相似文献
13.
Intact chloroplasts were isolated from mesophyll and bundlesheath protoplasts of a C 4 plant, Panicum miliaceum L., to measurethe uptake of [1- 14C]pyruvate into their sorbitol-impermeablespaces at 4?C by the silicone oil filtering centrifugation method.When incubated in the dark, both chloroplasts showed similarslow kinetics of pyruvate uptake, and the equilibrium internalconcentrations were almost equal to the external levels. Whenincubated in the light, only mesophyll chloroplasts showed remarkableenhancement of the uptake, the internal concentration reaching1030 times of the external level after 5 min incubation.The initial uptake rate of the mesophyll chloroplasts was enhancedabout ten fold by light and was saturated with increasing pyruvateconcentration; K m and V max were 0.20.4 mM and 2040µmol(mg Chl) 1 h 1, respectively. The lightenhancement was abolished by DCMU and uncoupling reagents suchas carbonylcyanide- m-chlorophenylhydrazone and nigericin. Theseresults indicate the existence of a light-dependent pyruvatetransport system in the envelope of mesophyll chloroplasts of P. miliaceum. The uptake activity of mesophyll chloroplastsboth in the light and the dark was inhibited by sulfhydryl reagentssuch as mersalyl and p-chloromercuriphenylsulfonate, but thebundle sheath activity was insensitive to the reagents. Thesefindings are further evidence for the differentiation of mesophylland bundle sheath chloroplasts of a C 4 plant with respect tometabolite transport. (Received July 3, 1986; Accepted October 8, 1986) 相似文献
14.
The effect of tribenzylphosphate on the activity of the phosphatetranslocator of intact pea chloroplasts was tested. The translocatoractivity was followed by O 2 evolution, 14CO 2 fixation and 32Pback-exchange. The reagent inhibited 3-phosphoglycerate dependent-photosyntheticactivities probably through an interaction with the PGA translocator. (Received September 11, 1985; Accepted November 21, 1985) 相似文献
15.
The enzyme content and functional capacities of mesophyll chloroplasts from Atriplex spongiosa and maize have been investigated. Accompanying evidence from graded sequential blending of leaves confirmed that mesophyll cells contain all of the leaf pyruvate, P i dikinase, and PEP carboxylase activities and a major part of the adenylate kinase and pyrophosphatase. 3-Phosphoglycerate kinase, NADP glyceraldehyde-3-P-dehydrogenase, and triose-P isomerase activities were about equally distributed between mesophyll and bundle sheath cells but other Calvin cycle enzymes were very largely or solely located in bundle sheath cells. In A. spongiosa extracts of predominantly mesophyll origin the proportion of the released pyruvate, P i dikinase, adenylate kinase, pyrophosphatase, 3-phosphoglycerate kinase, and NADP glyceraldehyde-3-P dehydrogenase retained in pelleted chloroplasts was similar but varied between 30 and 80% in different preparations. The proportion of these enzymes and NADP malate dehydrogenase recovered in maize chloroplast preparations varied between 15 and 35%. Washed chloroplasts retained most of the activity of these enzymes but ribulose diphosphate carboxylase and other Calvin cycle enzyme activities were undetectable. Among the evidence for the integrity of these chloroplasts was their capacity for light-dependent conversion of pyruvate to phosphoenolpyruvate and O 2 evolution when 3-phosphoglycerate or oxaloacetate were added. These results support our previous conclusions about the function of mesophyll chloroplasts in C 4-pathway photosynthesis and clearly demonstrate that they lack Calvin cycle activity. 相似文献
16.
The phosphate translocator protein of C 3 and C 4 mesophyll chloroplast envelopes was specifically labeled using the anion exchange inhibitor, 1,2-ditritio-1,2-(2,2′ -disulfo-4,4′ -diisothiocyano) diphenylethane ([ 3H] 2-DIDS). Intact mesophyll chloroplasts were isolated from the C 3 plants, Spinacia oleracea L. (spinach) and Pisum sativum L. (pea), and the C 4 plant, Zea mays L. (corn). Chloroplasts were incubated with 5 to 50 μ m [ 3H] 2-DIDS and, in addition, pea chloroplasts were also incubated with pyridoxal phosphate/tritiated sodium borohydride. The chloroplasts were washed, the envelopes isolated and solubilized. Following sodium dodecyl sulfate polyacrylamide gel electrophoresis, label from bound [ 3H] 2-DIDS was detected only in the 28- to 30-kilodalton protein (proposed C 3 phosphate translocator) for both C 3 and C 4 chloroplasts, as demonstrated by fluorography. In contrast, when pyridoxal phosphate/tritiated sodium borohydride was used to label pea chloroplasts, radioactivity was detected in several other bands in addition to the 29-kilodalton polypeptide. These findings suggest that DIDS is a much more specific inhibitor than reagents previously employed to study the phosphate translocator and could be used to isolate and characterize the differences in the C 3 and C 4 phosphate translocator protein(s). 相似文献
17.
C 4 cereals ( Zea maya L. and Sorghum bicolor L. Moench) and C 3cereals ( Triticum aestivum L. and Hordeum vulgare L) were grownin nutrient solutions with constant, interrupted, or absentpotassium supply. The lack of potassium retarded shoot growthand depressed the chlorophyll accumulation in all species ina similar way. After the renewal of potassium, the differencesin the compensation for growth retardation were not correlatedwith the photosynthetic system, but with the recovery of chlorophyllaccumulation in younger leaves. As important for the compensationof shoot growth retardation was a slower senescence of old leavescompared to plants with a constant potassium supply. This wasshown by the chlorophyll content and PEP carboxylase activity.In contrast to C 3 cereals, the C 4 cereals did not react withhigher chlorophyll contents to the same extent after the renewalof the postassium supply. The PEP carboxylase activity, however,was immediately raised higher than in control leaves. Chlorophylland PEP carboxylase activity increased simultaneously only inless aged leaves. 相似文献
18.
Bundle sheath protoplasts (BSP) were isolated and purified fromfour C 4 species of the phosphoenolpyruvate (PEP) carboxykinasetype ( Panicum maximum, P. texanum, Chloris gayana and Eriochloaborumensis), and cell organellses were separated from the BSPextract by differential centrifugation or sucrose density gradientcentrifugation. Separation of the organelles was ascertainedby the distribution of marker enzymes for chloroplasts, mitochondria,peroxisomes and cytoplasm. Contrary to the previous report [Rathnamand Edwards (1975) Arch. Biochem. Biophys. 171: 214], the distributionof PEP carboxykinase in BSP of P. maximum was the same as thatof UDP-glucose pyrophosphorylase, a marker for cytoplasm, andPEP carboxykinase activity was not recovered in the intact chloroplasts.The same results were obtained with P. texanum, C. gayana and E. borumensis. Therefore, we conclude that PEP carboxykinase is exclusivelylocalized in the cytoplasm of bundle sheath cells of C 4 plants. (Received July 23, 1983; Accepted October 17, 1983) 相似文献
19.
Intact mesophyll and bundle sheath chloroplasts wee isolated from the NADP-malic enzyme type C 4 plants maize, sorghum (monocots), and Flaveria trinervia (dicot) using enzymic digestion and mechanical isolation techniques. Bundle sheath chloroplasts of this C 4 subgroup tend to be agranal and were previously reported to be deficient in photosystem II activity. However, following injection of intact bundle sheath chloroplasts into hypotonic medium, thylakoids had high Hill reaction activity, similar to that of mesophyll chloroplasts with the Hill oxidants dichlorophenolindophenol, p-benzoquinone, and ferricyanide (approximately 200 to 300 micromoles O 2 evolved per mg chlorophyll per hour). In comparison to that of mesophyll chloroplasts, the Hill reaction activity of bundle sheath chloroplasts of maize and sorghum was labile and lost activity during assay. Bundle sheath chloroplasts of maize also exhibited some capacity for 3-phosphoglycerate dependent O 2 evolution (29 to 58 micromoles O 2 evolved per milligram chlorophyll per hour). Both the mesophyll and bundle sheath chloroplasts were equally effective in light dependent scavenging of hydrogen peroxide. The results suggest that both chloroplast types have noncyclic electron transport and the enzymology to reduce hydrogen peroxide to water. The activities of ascorbate peroxidase from these chloroplast types was consistent with their capacity to scavenge hydrogen peroxide. 相似文献
20.
The mechanism of light-dependent active transport of pyruvatein C 4 mesophyll chloroplasts has not been clarified, particularlyin Na +-type C 4 species, in which the pyruvate uptake into mesophyllchloroplasts is enhanced by illumination or by making a Na +gradient (Na +-jump) across the envelope in the dark. We re-investigatedhere the effect of Na + on the active transport of pyruvate inmesophyll chloroplasts of Panicum miliaceum, a Na +-type C 4 species,by comparing the rate of pyruvate uptake at various externalpHs under four conditions; in the light and dark together with/withoutNa +-jump: (1) At neutral pH, the rate of pyruvate uptake inthe dark was enhanced by Na +-jump but scarcely by illumination.(2) While the enhancement effect by Na +-jump was independentof external pH, that by illumination increased greatly at pHover 7.4, and the effects of light and Na + at the alkaline pHwere synergistic. (3) The light-enhanced pyruvate uptake wasrelated to stromal alkalization induced by illumination. Infact, pyruvate uptake was induced by H +-jump in the medium frompH 8.0 to 6.7. (4) Stromal pH was lowered by the addition ofK +-pyruvate and more by Na +-pyruvate into the medium at pH 7.8in the light. (5) However, the pH and ATP levels in the stromawere not affected by Na +-jump. Thus, we discussed possibility that besides pyruvate/Na + cotransportat neutral pH in the medium, pyruvate/H + cotransport enhancedby the presence of Na+ operates in mesophyll chloroplasts ofNa +-type C4 species at alkaline medium.
1Present address: Biological Resources Division, Japan InternationalResearch Center for Agricultural Sciences (JIRCAS), Ministryof Agriculture, Forestry and Fisheries, 2-1 Ohwashi, Tsukuba,305 Japan 相似文献
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