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1.
The effect of oxygen on photosynthetic 14CO 2 fixation in theair-grown freshwater flagellate Chroomonas sp. (Cryptophyta)was studied. Considerable inhibition by anaerobiosis was observedonly under light-saturated conditions with no effect from theCO 2 concentration. This inhibition was reversed by 2% O 2. With,more than 2% O 2, the rate of 14CO 2 fixation was inhibited; 100%O 2 caused about 20% inhibition which could be reversed by 2%O 2. The degree of inhibition was only slightly higher at lowconcentrations (less than 0.43 mM NaHCO 3) than at high CO 2 concentrations,indicating that photorespiration is not a main cause of thisinhibition. Possible causes of the inhibitions by anaerobiosisand by oxygen are discussed. (Received June 29, 1983; Accepted January 23, 1984) 相似文献
2.
In "air-grown" Chroomonas sp. cells, low concentrations of DCMU(less than 0.1 µM) could prevent the inhibition of 14CO 2fixation by anaerobiosis under light-saturating conditions (morethan 40 W.m 2), with phenazine methosulfate showing asimilar effect. Antimycin A, carbonyl cyanide m-chlorophenylhydrazone(CCCP), and N, N'-dicyclohexylcarbodiimide strongly inhibitedanaerobic photosynthesis at concentrations which did not significantlyinhibit the rate under 2% O 2 at high light intensity (200 W.m 2),although 0.2 µM CCCP stimulated the rate under 2% O 2 tosome extent. On the other hand, KCN inhibited the rate muchmore strongly under 2% O 2 than N 2, although it inhibited therate very strongly at concentrations above 5 µM both underN 2 and 2% O 2. These results suggest that the inhibition of photosynthetic 14CO 2 fixation by anaerobiosis in this alga result from ATPdeficiency caused by over-reduction of electron carriers ofthe cyclic electron flow and that oxygen can prevent the over-reduction.Cyclic electron flow seems to be necessary to provide additionalATP for CO 2 reduction under anaerobic conditions, although itseems to be less necessary under aerobic conditions. (Received July 21, 1983; Accepted January 23, 1984) 相似文献
3.
Suspensions of dark-adapted guard cell protoplasts of Vicia faba L. alkalinized their medium in response to irradiation with red light. The alkalinization peaked within about 50 minutes and reached steady state shortly thereafter. Simultaneous measurements of O 2 concentrations and medium pH showed that oxygen evolved in parallel with the red light-induced alkalinization. When the protoplasts were returned to darkness, they acidified their medium and consumed oxygen. Both oxygen evolution and medium alkalinization were inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). In photosynthetically competent preparations, light-dependent medium alkalinization is diagnostic for photosynthetic carbon fixation, indicating that guard cell chloroplasts have that capacity. The striking contrast between the responses of guard cell protoplasts to red light, which induces alkalinization, and that to blue light, which activates proton extrusion, suggests that proton pumping and photosynthesis in guard cells are regulated by light quality. 相似文献
4.
To examine 14CO 2 fixation, potential translocation, and carbonflow among leaf chemical fractions of young developing leaves,the shoot tip of 24-leaf cottonwood ( Populus deltoides Bartr.ex. Marsh) plants were cut off under water, placed in artificialxylem sap, and treated with 14CO 2 in continuous and pulse-chaseexperiments. Additional leaves on whole plants were spot treatedon the lamina tip to follow export from the tip only. The analysedleaves ranged in age from leaf plastochron index(LPI) 5to 3, the spot treated leaves from LPI 2 to 5. After 30 minfixation, the specific activity in the lamina tip increasedlinearly with leaf age from LPI 5 to 1 (0.5 to 4.5 kBqmg 1). Specific activity in the lower lamina increasedslowly with leaf age and did not reach 500 kBq mg 1 untilLPI 1. Total 14CO 2 fixed in the lower lamina exceededthat fixed in the tip by LPI 2 because of the large amountof tissue present in the lower lamina. Although the lamina tipfixed high levels of 14CO 2, pulse-chase studies coupled withautoradiography indicated no vein loading or translocation fromthe tip until about LPI 4 or 5. The 14C fixed in both tip andlower lamina was incorporated at the site of fixation and wasnot distributed to younger tissue or translocated from the lamina.Although the percentage distribution ( 14C in each chemical fractioncompared with the total in all fractions) of 14C among certainchemical fractions, e.g. sugars, amino acids and proteins, indicatedthat the mesophyll of the tip was more mature than the lowerlamina, physiologically both leaf sectors were immature basedon the expected 14C distribution in mature tissue. Informationfrom this and other studies indicates that the extreme tip ofa developing cottonwood leaf first begins to export photosynthateabout LPI 4 or 5 on a 24-leaf plant. The first photosynthatetranslocated may be incorporated into the vascular tissues andmesophyll directly below the tip. However, as the tip continuesto mature photosynthate is translocated past the immature lowerlamina into the petiole and out of the leaf. Populus deltoides Bartr. ex. Marsh, eastern cottonwood, translocation, leaf development, 14C fixation, carbon metabolism 相似文献
6.
The photosynthetic carbon reduction cycle intermediates can be divided into three classes according to their effects on the rate of photosynthetic CO 2 evolution by whole spinach ( Spinacia oleracea) chloroplasts and on their ability to affect reversal of certain inhibitors (nigericin, arsenate, arsenite, iodoacetate, antimycin A) of photosynthesis: class I (maximal): fructose 1, 6-diphosphate, dihydroxyacetone phosphate, glyceraldehyde-3-phosphate, ribose-5-phosphate; class 2 (slight): glucose 6-phosphate, fructose 6-phosphate, ribulose-1, 5-diphosphate; class 3 (variable): glycerate 3-phosphate. While class 1 compounds influence the photosynthetic rate, they do not lower the Michaelis constant of the chloroplast for bicarbonate or affect strongly other photosynthetic properties such as the isotopic distribution pattern. It was concluded that the class 1 compounds influence the chloroplast by not only supplying components to the carbon cycle but also by activating or stabilizing a structural component of the chloroplast. 相似文献
7.
A system has been developed for the study of photosynthetic CO 2 fixation by isolated spinach chloroplasts at air levels of CO 2. Rates of CO 2 fixation were typically 20 to 60 micromoles/milligrams chlorophyll per hour. The rate of fixation was linear for 10 minutes but then declined to less than 10% of the initial value by 40 minutes. Ribulose 1,5-bisphosphate (RuBP) levels remained unchanged during this period, indicating that they were not the cause for the decline. The initial activity of the RuBP carboxylase in the chloroplast was high for 8 to 10 minutes and then declined similar to the rate of CO 2 fixation, suggesting that the decline in CO 2 fixation may have been caused by deactivation of the enzyme. 相似文献
8.
Photosynthetic carbon metabolism was characterized in four photoautotrophic cell suspension cultures. There was no apparent difference between two soybean (Glycine max) and one cotton ( Gossypium hirsutum) cell line which required 5% CO 2 for growth, and a unique cotton cell line that grows at ambient CO 2 (660 microliters per liter). Photosynthetic characteristics in all four lines were more like C 3 mesophyll leaf cells than the cell suspension cultures previously studied. The pattern of 14C-labeling reflected the high ratio of ribulosebisphosphate carboxylase to phospho enolpyruvate carboxylase activity and showed that CO 2 fixation occurred primarily by the C 3 pathway. Photorespiration occurred at 330 microliters per liter CO 2, 21% O 2 as indicated by the synthesis of high levels of 14C-labeled glycine and serine in a pulse-chase experiment and by oxygen inhibition of CO 2 fixation. Short-term CO 2 fixation in the presence and absence of carbonic anhydrase showed CO 2, not HCO 3−, to be the main source of inorganic carbon taken up by the low CO 2-requiring cotton cells. The cells did not have a CO 2-concentrating mechanism as indicated by silicone oil centrifugation experiments. Carbonic anhydrase was absent in the low CO 2-requiring cotton cells, present in the high CO 2-requiring soybean cell lines, and absent in other high CO 2 cell lines examined. Thus, the presence of carbonic anhydrase is not an essential requirement for photoautotrophy in cell suspension cultures which grow at either high or low CO 2 concentrations. 相似文献
9.
The metabolism of fixed 14CO 2 and the utilization of the C-4 carboxyl of malate and aspartate were examined during photosynthetic induction in Flaveria trinervia, a C 4 dicot of the NADP-malic enzyme subgroup. Pulse/chase experiments indicated that both malate and aspartate appeared to function directly in the C 4 cycle at all times during the induction period (examined after 30 seconds, 5 minutes and 20 minutes illumination). However, the rate of loss of 14C-label from the C-4 position of malate plus aspartate was relatively slow after 30 seconds of illumination, compared to treatments after 5 or 20 minutes of illumination. Similarly, the appearance of label in other photosynthetic products (e.g. 3-phosphoglycerate, sugar phosphates, alanine) during the chase periods was generally slower after only 30 seconds of leaf illumination, compared to that after 5 of 20 minutes illumination. This may be due to the lower rate of photosynthesis after 30 seconds illumination. The appearance of label in carbons 1→3 of each C 4 acid during the chase periods was relatively slow after either 30 seconds or 5 minutes illumination, while there was a relatively rapid accumulation of label in carbons 1→3 of both C 4 acids after 20 minutes illumination. Thus, while the turnover rate of the 14C-4 label in both C 4 acids increased only during the first 5 minutes of the induction period, only later during induction is there an increased rate of appearance of label in other carbon atoms of the C 4 acids. The implied source of 14C for labeling of the 1→3 positions of the C 4 acids is an apparent carbon flux from 3-phosphoglycerate of the reductive pentose phosphate pathway to phosphoenolpyruvate of the C 4 cycle. 相似文献
10.
Experiments are reported in which the effects on photosynthesisof various inhibitors of cyclic photophosphorylation were investigated.These inhibitors, generally had only a small inhibitory effecton photosynthesis, and the inhibition was not increased by conditionswhich inhibit pseudocyclic photophosphorylation. These inhibitorsdo not inhibit the Emerson enhancement effect. From these resultsit was concluded that photosynthesis does not need any ATP otherthan that produced in non-cyclic photophosphorylation. The effectsof these inhibitors on active K influx in light-anaerobic conditionsin the presence or absence of CO 2 suggest that some of the ATPproduced by non-cyclic photophosphorylation can be used to supportactive K influx. The results are discussed in relation to themechanism of the Emerson effect, the stoichiometry of non-cyclicphotophosphorylation, and the ATP requirements for autotrophicgrowth. 相似文献
12.
Products of the nodule cytosol in vivo dark [ 14C]CO 2 fixation were detected in the plant cytosol as well as in the bacteroids of pea ( Pisum sativum L. cv “Bodil”) nodules. The distribution of the metabolites of the dark CO 2 fixation products was compared in effective (fix +) nodules infected by a wild-type Rhizobium leguminosarum (MNF 300), and ineffective (fix −) nodules of the R. leguminosarum mutant MNF 3080. The latter has a defect in the dicarboxylic acid transport system of the bacterial membrane. The 14C incorporation from [ 14C]CO 2 was about threefold greater in the wild-type nodules than in the mutant nodules. Similarly, in wild-type nodules the in vitro phospho enolpyruvate carboxylase activity was substantially greater than that of the mutant. Almost 90% of the 14C label in the cytosol was found in organic acids in both symbioses. Malate comprised about half of the total cytosol organic acid content on a molar basis, and more than 70% of the cytosol radioactivity in the organic acid fraction was detected in malate in both symbioses. Most of the remaining 14C was contained in the amino acid fraction of the cytosol in both symbioses. More than 70% of the 14C label found in the amino acids of the cytosol was incorporated in aspartate, which on a molar basis comprised only about 1% of the total amino acid pool in the cytosol. The extensive 14C labeling of malate and aspartate from nodule dark [ 14C]CO 2 fixation is consistent with the role of phospho enolpyruvate carboxlase in nodule dark CO 2 fixation. Bacteroids from the effective wild-type symbiosis accumulated sevenfold more 14C than did the dicarboxylic acid transport defective bacteroids. The bacteroids of the effective MNF 300 symbiosis contained the largest proportion of the incorporated 14C in the organic acids, whereas ineffective MNF 3080 bacteroids mainly contained 14C in the amino acid fraction. In both symbioses a larger proportion of the bacteroid 14C label was detected in malate and aspartate than their corresponding proportions of the organic acids and amino acids on a molar basis. The proportion of 14C label in succinate, 2-oxogultarate, citrate, and fumarate in the bacteroids of the wild type greatly exceeded that of the dicarboxylate uptake mutant. The results indicate a central role for nodule cytosol dark CO 2 fixation in the supply of the bacteroids with dicarboxylic acids. 相似文献
13.
When isolated spinach chloroplasts are illuminated, photosynthesis and CO 2 fixation die off within 30 to 90 minutes. Even when air levels of CO 2 are used which maintain high and rate-saturating amounts of ribulose 1,5-bisphosphate inside the plastids, CO 2 fixation declines. The decline begins with a drop in activity of the ribulose 1,5-bishosphate carboxylase/oxygenase, specifically loss of the enzyme-activator CO 2-Mg 2+ form. Next, the light reactions cause gradual leakage of the carboxylase and other stromal proteins to the suspending medium. The chloroplast outer envelope appears to reseal and protect the thylakoids since there is little change in the ferricyanide-dependent Hill reaction. In the dark, under otherwise identical conditions, leakage of carboxylase does not occur. 相似文献
14.
Phosphoenolpyruvate carboxylase was purified from corn root tips about 80-fold by centrifugation, ammonium sulfate fractionation, and anion exchange and gel filtration chromatography. The resulting preparation was essentially free from malate dehydrogenase, isocitrate dehydrogenase, malate enzyme, NADH oxidase, and pyruvate kinase activity. Kinetic analysis indicated that l-malate was a noncompetitive inhibitor of P-enolpyruvate carboxylase with respect to P-enolpyruvate (K I = 0.8 m m). d-Malate, aspartate, and glutamate inhibited to a lesser extent; succinate, fumarate, and pyruvate did not inhibit. Oxaloacetate was also a noncompetitive inhibitor of P-enolpyruvate carboxylase with an apparent K I of 0.4 m m. A comparison of oxaloacetate and l-malate inhibition suggested that the mechanisms of inhibition were different. These data indicated that l-malate may regulate CO 2 fixation in corn root tips by a feedback or end product type of inhibition. 相似文献
15.
Methionine sulfoximine (MSO) greatly reduced the carbon dioxideexchange rate (CER) of detached wheat ( Triticum aestivvm L.cv Roland) leaves in 21% O 2, but only slightly reduced it in2% O 2. A supply of 50 mM NH 4Cl had little effect on the CERirrespective of the O 2 concentration. A simultaneous additionof glutamine and MSO protected against the inhibition of photosynthesisto a considerable extent and caused the accumulation of moreNH 3 than did the addition of MSO alone. Fixation of 14CO 2 in wheat leaves was inhibited by MSO treatmentin 22% O 2, and there was decreased incorporation of 14G intoamino acids and sugars and increased label into acid fractions.The addition of MSO and glutamine together eliminated the effectof MSO on the photosynthetic 14CO 2 fixation pattern. NH 4Cl stimulatedthe synthesis of amino acids from 14CO 2, especially the synthesisof serine in 22% O 2. Our observations show that factors other than the uncouplingof photophosphorylation by accumulated NH 3 may be responsiblefor the early stage of photosynthesis inhibition by MSO underphotorespiratory conditions.
1Present address: Department of Agricultural Chemistry, KyushuUniversity, Fukuoka 812 Japan.
2Also at U.S. Department of Agriculture, Agricultural ResearchService, Urbana, Illionois 61801, U.S.A. (Received September 13, 1983; Accepted February 2, 1984) 相似文献
16.
The enhanced dark CO 2 uptake after a preillumination period under varying O 2 concentrations has been measured with maize, a C 4 plant. For comparison the same study has been conducted with tomato, a C 3 plant. Increasing the O 2 concentration during preillumination inhibits by 70% the subsequent dark CO 2 uptake in tomato but stimulates 2-fold this CO 2 uptake in maize. The O 2 enhancement of CO 2 uptake in maize is due to the enhancement of malate and aspartate synthesis. The percentages of radioactivity incorporated in the C-4 of malate and aspartate vary from 74 to 87% when O 2 concentration during preillumination is increased from 0 to 100%. 相似文献
17.
Nonautotrophic CO 2 metabolism in Opuntia echinocarpa roots was studied with techniques of manometry and radiometry. The roots were grown in a one-quarter strength nutrient solution for several days; the distal 2 cm was used for physiological studies. The roots assimilated significant quantities of 14CO 2 and appeared to show a crassulacean-type acid metabolism with respect to quality and quantity. Most of the 14C activity was associated with the distal portion of the elongating root indicating correlation with metabolic activity. The 14CO 2 assimilation was comparable to a crassulacean leaf succulent, but 3 times greater than that found for stem tissue of the same Opuntia species. The rates of O2 and CO2 exchange and estimated CO2 fixation were 180, 123, and 57 μl/g per hour. A respiratory quotient of 0.66 was found. The products of 14CO2 fixation were similar in most respects to reported experiments with leaf succulents. Equilibration of the predominant malic acid with isocitric, succinic, and fumaric acids was not evident. The latter observation was interpreted as metabolic isolation of the fixation products rather than poor citric acid cycle activity. A rapid turnover of the fixed 14CO2 was measured by following decarboxlyation kinetics and by product analysis after a postincubation period. The first order rate constant for the steady state release was 4.4 × 10−3 min−1 with a half-time of 157.5 minutes. Amino acids decayed at a more rapid rate than organic acids. 相似文献
18.
Treatment of Chlamydomonas reinhardtii cells, cultured at 5% CO 2, with 1 to 1000 micrograms triacontanol (TRIA) per liter resulted in 21 to 35% increases in cell density, 7 to 31% increases in total chlorophyll, and 20 to 100% increases in photosynthetic CO 2 assimilation. The increase in CO 2 fixation with TRIA treatment occurred before, and was independent of, increases in total chlorophyll or cell number. Chlamydomonas cells responded to a broad range of TRIA concentrations that were at least one order of magnitude above the optimum concentration established for higher plants. The necessity for larger concentrations of TRIA may be due to destabilizing effects of Ca 2+ and K + present in the Chlamydomonas growth medium. These ions caused flocculation of the colloidally dispersed TRIA in apparent competition with binding of [ 14C]TRIA to Chlamydomonas cells. Octacosanol inhibited the effect of TRIA on photosynthetic CO 2 assimilation. TRIA treatment did not alter the distribution of 14C-label among photosynthetic products. The effect of TRIA on photosynthetic CO 2 assimilation increased with time after treatment up to 3 days. Chlamydomonas cells that had been grown at low-CO 2 (air) did not respond to TRIA, and transfer of high-CO 2 (5%) grown cells that had responded to TRIA to a low-CO 2 atmosphere resulted in a loss of the effect of TRIA. The effect of pH on photosynthetic CO 2 assimilation indicated that CO 2 is probably the species of inorganic carbon utilized by control and TRIA-treated Chlamydomonas cells. 相似文献
19.
Chloroplasts were isolated from the marine alga Codium vermilara (Siphonales). The isolated chloroplasts were active in CO 2 fixation in the light at a rate comparable to the rates obtained by fragments of thalli. Maximal rates of CO 2 fixation by isolated chloroplasts from Codium were obtained in the presence of salt or sorbitol isoosmotic with sea water. The conditions of isolation of Codium chloroplasts are much less stringent than those required for active chloroplasts from higher plants. The isolated chloroplasts comprise a homogeneous population of the intact “class I” type, as based on microscopic observations and on their inability to reduce ferricyanide unless osmotically shocked. The intact chloroplasts are able to reduce p-benzoquinone at a high rate. 相似文献
20.
Excised leaves of kidney bean plants treated with various concentrationsof atrazine for different periods were allowed to fix 14CO 2CO 2 fixation was inhibited by atrazine. The 14C-labelling patternof atrazine-treated leaves resembled dark Co 2-fixation patterns.The carbon-I-carboxyl group of 14C-aspartic acid from atrazine-treatedand dark leaves showed no significant differencesin total radioactivity. Although atrazine disrupted the photosyntheticapparatus, it seemed to have no effect on non-photosyntheticCO 2 fixation. 相似文献
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