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1.
Changes in the level of nicotinamide nucleotides, rate of 14CO2output from [1–14C] or [614 C6/C1 ratios, glucose-6-phosphatedehydrogenase, 6-phosphogluconate dehydrogenase, and NAD kinaseactivities were determined during the first 72 h of germinationof seeds of Cicer arietinum L. The level of oxidized and reducedforms of nicotinamide nucleotides, together with the activityof glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase,NAD kinase, and C6/C1 ratios, suggest that the pentose phosphatepathway is activated during early germination in cotyledonsof chick pea seeds. The results obtained in embryonic axes seemsto indicate a lower participation of the PP pathway, probablydue to the development of the activity of the glycolytic-TCApathway.  相似文献   

2.
Dehydroquinate synthase from Phaseolus mungo seedlings was purified120-fold by DE-23, hydroxylapatite and Sephadex G-100 columnchromatography. The final preparation was free of dehydroquinatehydro-lyase and NAD(P)H2 oxidase. The dehydroquinate synthaserequired Co2+ and NAD as cofactors. Co2+ could be replaced byCu2+ at 0.1 mM, but Cu2+ at higher levels was inhibitory. Noneof the other metal ions tested activated the enzyme. Some activitywas observed in the absence of added Co2+ and this activitywas inhibited by EDTA but not by diethyldithiocarbamate, NaN3or NaCN. Heavy metal ions, such as Ag+ and Hg2+, and p-chloromercuribenzoatestrongly inhibited the enzyme activity. Of the pyridine nucleotidestested only NAD was required for the maximum activity of theenzyme. In the absence of NAD, the enzyme retained 30 to 40%of the activity obtained with added NAD. The apparent Km valuefor DAHP at pH 7.4 was about 23 µM. The enzyme activityappeared to be maximum at about pH 8.5. However, the characteristicsof the enzyme were studied at pH 7.4, because of the labilityof the enzyme under alkaline conditions. An Arrhenius plot ofthe enzyme reaction showed a break at about 21?C, and belowthis critical temperature the activation energy increased. (Received March 4, 1977; )  相似文献   

3.
The pattern for primary products of CO2-fixation and the chloroplaststructure of Amaranthus retrqflexus L., a species which incorporatescarbon dioxide into C4 dicarboxylic acids as the primary productof photosynthesis, were compared in various chlorophyll containingtissues,i.e., foliage leaves, stems, cotyledons and pale-greencallus induced from stem pith. Despite some morphological differencesin these assimilatory tissues, malate and aspartate were identifiedas the major compounds labelled during a 10 sec fixation of14CO2 in all tissues. Whereas, aspartate was the major componentin C4-dicarboxylic acids formed in foliage leaves, malate predominatedas the primary product in stems, cotyledons and the pale-greencallus. The percentage of 14C-radioactivity incorporated intoPGA and sugar-P esters increased and 14C-sucrose was detectedin the prolonged fixation of 14CO2 in the light, not only infoliage leaves, but also in stems and cotyledons. 1 This work was supported by a Grant for Scientific ResearchNo. 58813, from the Ministry of Education, Japan. 2 Present address: Institute of Applied Microbiology, Universityof Tokyo, Tokyo, Japan. 3 Present address: Department of Biochemistry, University ofGeorgia, Athens 30601. Georgia, U. S. A. (Received July 10, 1971; )  相似文献   

4.
The pathway of glutamine synthesis in germinating castor beanendosperm was investigated by feeding experiments with (2,3-14C)succinateand by determining enzyme activities related to pyruvate formationand utilization. 14C of (2,3-14C)succinate was rapidly and sequentiallyincorporated into amino acids in the following order: aspartateor alanine, glutamate and glutamine. 14CO2 was slowly released,especially during the early hours of incubation. Fluorocitrateinhibited 14CO2 release while aminooxyacetate stimulated itslightly. Fluorocitrate inhibited the incorporation of 14C intoglutamate and glutamine. Aminooxyacetate inhibited 14C incorporationinto aspartate, alanine, glutamate and glutamine. Glutaminesynthetase activity was detected in a soluble fraction. NAD-malicenzyme activity was detected in mitochondria by sucrose densitygradient centrifugation. Activities of pyruvate decarboxylaseand aldehyde dehydrogenasewere detected. Aldehyde dehydrogenasewas partially purified about 60-fold by ammonium sulfate fractionationand the DEAE-cellulose chromatography. The Km values of theenzyme were 0.71 miu for NAD and 0.43 mM for acetaldehyde. Basedon these results and properties of pyruvate kinase reportedpreviously (9), the metabolism of pyruvate in cytosol and mitochondriawas discussed in connection with glutamine synthesis in germinatingcastor bean endosperm. (Received August 25, 1978; )  相似文献   

5.
Leaf extract of Sedum mexicanum, a typical CAM plant, decarboxylated14C-aspartate to form 14C-alanine. The reaction was activatedby the addition of 2-oxoglutarate and pyridoxal 5'-phosphate,while other keto acids had no effect on the reaction. The possiblepresence of aspartate 4-decarboxylase is discussed in relationto the participation of other enzymes concerned. (Received September 6, 1980; Accepted December 17, 1980)  相似文献   

6.
The influence of varying light intensity and quality on thecarbon labelling patterns in Rumex vesicarius (a C3 plant),Setaria italica (a malate-formingC4 plant), and Amaranthus paniculatus(an aspartate-forming C4 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 C4 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 C4-photosynthesis in Setariaand Amaranthus. Leaves of S. italica and A. paniculatus were allowed to photosynthesizein 14CO2 for 5 s and then the distribution of the labelled productsbetween the mesophyll and the bundle sheath cells was determinedduring subsequent photosynthesis in 12CO2. 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   

7.
When 14CO2 was fed to flag leaf laminae at 20 d post-anthesis,the transport organs between the leaf and the grains containedappreciable 14C in glutamine, glutamate, serine, alanine, threonineand glycine. Smaller amounts of 14C were present in gamma-aminobutyricacid (GABA), aspartate and cysteine. Other amino acids whichwere labelled in the source leaf were not labelled in the transportorgans. The export of labelled glutamine, serine, glycine andthreonine from the source leaf was favoured in comparison tothe other amino acids mentioned. Threonine accumulated, andwas subsequently metabolised, in the rachis. [14C]GABA alsoaccumulated in the rachis. In the grains, the relative amountof soluble [14C]alanine increased with chase time. This wasprobably due to de novo synthesis and reflected the specialrole of alanine in grain nitrogen metabolism. Wheat, Triticum aestivum, 14CO2, amino acids, transport, carbon metabolism  相似文献   

8.
1) With Chlorella ellipsoidea cells, in the presence of 5x10–6M DSPD, or in its absence, the amounts of 14CO2 incorporatedin P-esters, serine-plus-glycine and alanine were larger underred light than under blue light, whereas blue light specificallyincreased 14CO2-incorporation in aspartate, glutamate, malateand fumarate (blue light effect). The amount of total 14C fixedunder blue or red light was greatly decreased by the additionof DSPD. When the concentration of DSPD was raised to 5x10–4M, practically no radioactivity was found, under blue or redlight, in aspartate, glutamate and fumarate. Radioactivity inalanine was greatly increased. Effects of higher concentrationof DSPD are explained as due to the inhibition of PEP carboxylaseactivity in Chlorella cells. 2) The percentage incorporation of 14C into aspartate and theother compounds mentioned above, under near infra-red illuminationwas significantly smaller than that under blue light and wasalmost equal to that under red light. These results along withthe effect of 5x10–6 M DSPD, exclude the possibility thatcyclic photophosphorylation is involved in the "blue light effect"mechanism. (Received December 12, 1969; )  相似文献   

9.
The metabolic transformation of glycine into serine in the photosyntheticbacterium Chromatium vinosum was accompanied by the evolutionof CO2 due to decarboxylation of glycine. Isonicotinylhydrazideinhibited both 14CO2 evolution and the formation of 14C-serinefrom 14C-glycine. The results indicate that a glycine-serinetransformation reaction takes place which is analogous to thatoccurring in green leaf tissues. Glycine may be metabolisedthrough serine by this reaction. The light stimulation of 14CO2evolution and 14C-serine formation from 14C-glycine by the Chromatiumcells are judged to be results of the light-induced enhancementof 14C-glycine uptake by the bacterial cells. 1This is paper 53 in the series "Structure and Function of ChloroplastProteins" and paper 7 of the series "Biosynthetic Mechanismof Glycolate in Chromatium". Paper 6 of the latter series isRef. 3 by Asami and Akazawa (1978). 2This study was aided by research grants from the Ministry ofEducation, Science and Culture of Japan and the Nissan ScienceFoundation (Tokyo). 3Postdoctoral Fellow (1980) of the Japan Society for the Promotionof Science. (Received May 20, 1980; )  相似文献   

10.
The activities of Hill reaction and photosynthetic 14CO2 fixationin bundle sheath strands enzymatically isolated from millet(Panicum miliaceum) were 3–15 times as high as those observedin corn (Zea mays). In both preparations, 3-phosphoglyceratewas the initial 14CO2 fixation product and the radioactivitywas incorporated into sucrose and insoluble compounds (glucose-polymers)during the later period. After 20 sec of photosynthetic 14CO2fixation, the percent of 14C incorporated into sugar phosphatesin millet was about 3 times as high as that in corn, while incorn, the percent of 14C in 3-phosphoglycerate was higher thanthat observed in millet throughout the experimental period.When 14C-phosphoglycerate was added to the isolated bundle sheathstrands, the rates of transfer of the radioactivity to dihydroxyacetonephosphate and sugar diphosphates in millet were significantlyhigher than those in corn. These results indicate that in thebundle sheath strands isolated from corn in which photosystemII activity is deficient, the reductive pentose cycle is impairedat the reduction step of 3-phosphoglycerate to glyceraldehydephosphate due to the limited supply of NADPH through the photoelectrontransport system. In contrast, the bundle sheath strands isolatedfrom millet which have adequate photosystem II activity cancarry out normal photosynthetic CO2 fixation. (Received January 23, 1975; )  相似文献   

11.
The utilization of inorganic carbon and role of the coccolithswere investigated in intact cells and protoplasts of a marineunicellular calcareous alga, Emiliania huxleyi. Protoplastswith high photosynthetic activity were obtained by artificialdecalcification with 50 mM MES-NaOH (pH5.5). (1) The kineticsof the photosynthetic evolution of O2 at various concentrationsof externally added NaHCO3 were the same for intact cells andprotoplasts, indicating that the kinetic properties with respectto dissolved inorganic carbon (DIC) were not affected by thepresence or absence of the coccoliths on the cell surface. Double-reciprocalplots and plots of the concentration of substrate divided byvelocity (s/v) against the concentration of substrate (s) werebiphasic in the case of both intact cells and protoplasts. TheCO2-utilization reaction was, therefore, considered to involvetwo processes with different values of Km and Vmax. From thekinetic analyses, Km and Vmax [µmoles O2 (ml PCV)–1h–1] were deduced to be 92 µM and 76.3 for a "low-Km"reaction and 4.1 mM and 252 for a "high-Km" reaction, respectively.(2) In short-term (40-min) experiments, time courses of thetotal uptake of 14C-DIC and the incorporation of 14C into acid-stableproducts of photosynthesis and the internal pool of DIC, determinedas acid-labile compounds, under CO2-limiting conditions (80µM) were very similar for intact cells and protoplasts.However, incorporation of 14C into CaCO3 apparently occurredmore slowly in protoplasts than in intact cells. (3) In longterm (24-h) experiments, patterns of incorporation of 14C werealmost same for intact cells and protoplasts, with the exceptionthat the amount of 14C incorporated into CaCO3 was much smallerin the former than the latter. The production of Ca14CO3 increasedduring the course of 10 h after a 4-h lag. However, after 10h the level of Ca14CCO3 started to decrease. The decrease wasaccompanied by an increase in 14C in the products of photosynthesis,suggesting that CaCO3 was reutilized for the photosyntheticfixation of CO2 and, therefore, that the coccoliths functionas sites of storage of DIC. However, the internal level of DICremained at the same level even after the supply of externalDIC has been almost completely depleted. (Received July 25, 1995; Accepted December 11, 1995)  相似文献   

12.
Seeni  S.; Gnanam  A. 《Plant & cell physiology》1983,24(6):1033-1041
Photomixotrophic cell suspension culture was established fromthe leaf derived callus cells of Gisekia pharnaceoides L., aC4 dicotyledonous weed. The late log phase cells possessed shade-typecharacters such as low chlorophyll a/b ratio, less pronouncedO2 evolution and CO2 fixation, saturation of photosyntheticCO2 fixation at low intensity. The chloroplasts from these cellscontained granal stacking with high degree of a very few granawhich are characterized by their wide and high degree of stackings. The predominant labelling of 3-phosphoglyceric acid and sugarphosphates (40% of the total 14C incorporated) during 5 s exposureto 14CO2 in light and subsequent decrease in percentage of 14Cin these compounds with increase in exposure time indicatedthe operation of the C3 pathway in these cells. The simultaneoussynthesis of malate (23% of the total 14C incorporated) is relatedto the much pronounced glycolytic and tricarboxylic acid cycleactivities in these cells. The initial proliferation of callimainly from the zones of vascular supplies in the leaf, highstarch content of the cells, presence of large starch grainsin all the chloroplasts, activities of Calvin cycle enzymes,heavy labelling of C3 type intermediates and less labellingof aspartate as early photosynthates and rapid accumulationof radioactivity into starch during 14CO2 assimilation indicatedthat most of the cells in photomixotrophic culture were derivedfrom bundle sheath cells or the leaf cells of Gisekia changetheir function under culture conditions. 1Present address: Tropical Botanic Garden and Research Institute,Navaranga Road, Trivandrum 695 011, India. (Received January 29, 1982; Accepted June 4, 1983)  相似文献   

13.
Chlorella cells incubated in the dark longer than 12 hr showedpronounced blue light-induced 14CO2 fixation into aspartate,glutamate, malate and fumarate (blue light effect), whereasthose kept under continuous light showed only a slight bluelight effect, if any. 2) During dark incubation of Chlorellacells, phosphoenolpyruvate carboxylase activity and the capacityfor dark 14CO2 fixation decreased significantly, whereas ribulose-1,5-diphosphatecarboxylase activity and the capacity for photosynthetic 14CO2fixation (measured under illumination of white light at a highlight intensity) did not decrease. 3) In cells preincubatedin the dark, intracellular levels of phosphoenolpyruvate and3-phosphoglycerate determined during illumination with bluelight were practically equal to levels determined during illuminationwith red light. 4) The blue light effect was not observed incells incubated widi chloramphenicol, indicating that blue light-inducedprotein synthesis is involved in the mechanism of the effect. (Received April 9, 1971; )  相似文献   

14.
15.
The mechanism by which malate synthesis from CO2 is increasedunder low concentrations of CO2 was investigated in C3 plants.A number of metabolites were administered to illuminated tomatoleaves, and their effects on the incorporation of 14CO2 intomalate were determined. Compared with water as a control, glycolate,glyoxylate, D,L-glycerate, glycine, phosphoglycolate and L-serineincreased malate synthesis by factors of 6.8, 3.8, 3.3, 2.5,2.3 and 2.2, respectively. The effect of exogenous glycolateon malate synthesis from CO2 was dependent on its concentrationup to 100 mu, but was independent of ambient CO2 concentration.The feeding of l-14C-glycolate in the light indicated that glycolatestimulated the carbon flow from CO2 to malate. The analysis of the products of 14CO2 fixation in illuminatedleaves supplied with glycolate showed increases in malate andsugar and decreases in serine and phosphate esters. However,this stimulated malate synthesis ceased when malonate was suppliedsimultaneously with glycolate. Treatment with glycolate didnot affect the dark 14CO2-fixation, but increased the 14C-malatesynthesis, with a corresponding decrease in 14C-aspartate and14C-glutamate. These results suggest that exogenous glycolateactivates malate dehydrogenase in leaves, and that the increasedglycolate formation at low CO2 concentrations is associatedwith the increased malate synthesis from CO2. (Received January 12, 1981; Accepted May 20, 1981)  相似文献   

16.
Addition of 2 mM ammonium ion to isolated mesophyll cells ofPapaver somniferum resulted in a 3-fold or greater increasein their rate of dark 14C fixation, while even 0.1 mM NH4+ nearlydoubled that rate. The most rapid increase in the labeling ofa metabolite occurred in aspartate, and was accompanied by adecrease in the steady-state level of labeled phosphoenolpyruvate.No change in labeled pyruvate level occurred, and alanine labelingdeclined. Ammonium ion addition had no effect on the respiratoryrate of these cells in the dark. We conclude that NH4+ stimulatesphosphoenolpyruvate carboxylation in this system, but has nodetectable effect on the pyruvate kinase reaction in the dark.Our results are compared with earlier findings and the possibleregulatory function of ammonia is discussed. (Received July 23, 1979; )  相似文献   

17.
Dark CO2 fixation by Anabaena cylindrica was stimulated aboutthree-fold by the addition of NH4Cl to the cells. The 14CO2incorporation experiments showed that 14C is most rapidly incorporatedinto aspartate and then glutamine by adding NH4CI. Glutamineaccumulated predominantly after the addition of NH4Cl showingthat NH4 is incorporated into glutamine by glutamine synthetase.The stimulating effect of NH4Cl on CO2 fixation and amino acidsynthesis was suppressed by methionine sulfoximine, an inhibitorof glutamine synthetase. It was suggested that dark CO2 fixationwas stimulated by the action of glutamine synthesis which isenhanced by ammonia. (Received February 10, 1981; Accepted April 2, 1981)  相似文献   

18.
Pericarps of Datura stramomum L. photosynthesizing in 14CO2,have been shown to contribute amino acids (especially aspartate,threonine, serine, glutamate, glycine, alanine, phenylalanine,lysine, and histidine) to the protein-bound amino acids of theseed. This contribution is, however, a relatively minor onein comparison with the contribution made by photosyntheaizingleaves in the close proximity of the fruit.  相似文献   

19.
The metabolic transformation of glycolate to glycine occurringin photosynthesizing cells of Chromatium was investigated bythe radioisotopic technique and by amino acid analysis. By analyzingthe distribution of radiocarbon upon feeding [1-14C] glycolate,[2-14C] glyoxylate and [1-14C] glycine to bacterial cells, itwas demonstrated that glycolate is converted to glycinc viaglyoxylate, and both glycolate and glycine are excreted extracellularly.Although the formation of serine was barely detected by theabove two techniques in both N2 and O2 atmospheres, it was foundthat 14CO2 is evolved quite markedly from both [1-14C] glycolateand [1-14C] glycine fed to the Chromatium cells. Analyticalresults of transient changes in amino acid compositions underatmospheric changes of N2O2 and by the addition of exogenousglycolate in N2 confirm the notion that glycolate is convertedto glycine. Acidic amino acids (glutamic acid and aspartic acid)appear to take part in glycine formation as amino donors. Theformation of glycine from glycolate in a N2 atmosphere suggeststhat an unknown glycolate dehydrogenation reaction may operatein the overall process. 1 This is paper XXXVII in the series ‘Structure and Functionof Chloroplast Proteins’. Paper XXXVI is ref. (5). Theresearch was supported in part by grants from the Ministry ofEducation of Japan (No. 111912), the Toray Science Foundation(Tokyo) and the Naito Science Foundation (Tokyo). (Received July 14, 1976; )  相似文献   

20.
The capacity for C4 photosynthesis in Panicum milioides, a specieshaving reduced levels of photorespiration, was investigatedby examining the activity of certain key enzymes of the C4 pathwayand by pulse-chase experiments with 14CO2. The ATP$P1 dependentactivity of pyruvate,P1 dikinase in the species was extremelylow (0.14–0.18 µmol mg chlorophyll–1 min–1).Low activity of the enzyme was also found in Panicum decipiensand Panicum hians (related species with reduced photorespiration)and in Panicum laxum (a C3 species). The antibody to pyruvate,P1dikinase caused about 70% inhibition of the ATP$P1 dependentactivity of the enzyme in P. milioides. The activity of NAD-malicenzyme and NADP-malic enzyme in P. milioides was equally low(approximately 0.1–0.2 µmol mg chlorophyll–1min–1) and similar to the activity in P. decipiens, P.hians and P. laxum. Photosynthetic pulse-chase experiments underatmospheric conditions showed a typical C3-like pattern of carbonassimilation including the labelling of glycine and serine asexpected during photorespiration. During the pulse with 14CO2only about 1% of the labelled products appeared in malate and2–3% in aspartate. During a chase in atmospheric levelsof CO2 for up to 6 min there was a slight increase in labellingin the C4 acids. The amount of label in carbon 4 of aspartatedid not change during the chase, indicating little or no turnoverof the C4 acid via decarboxylation. The results indicate thatunder atmospheric conditions P. milioides assimilates carbondirectly through the C3 pathway. Photorespiration as indicatedby the CO2 compensation point may be repressed in the speciesby a more efficient recycling of photorespired CO2. (Received June 8, 1982; Accepted July 22, 1982)  相似文献   

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