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1.
In "air-grown" Chroomonas sp. cells, low concentrations of DCMU(less than 0.1 µM) could prevent the inhibition of 14CO2fixation by anaerobiosis under light-saturating conditions (morethan 40 W.m2), 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% O2 at high light intensity (200 W.m2),although 0.2 µM CCCP stimulated the rate under 2% O2 tosome extent. On the other hand, KCN inhibited the rate muchmore strongly under 2% O2 than N2, although it inhibited therate very strongly at concentrations above 5 µM both underN2 and 2% O2. These results suggest that the inhibition of photosynthetic14CO2 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 CO2 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
2.
Photosynthetic carbon metabolism was studied with Chroomonassp. cells in which the rate of photosynthesis was inhibitedunder both an anaerobic condition and high concentrations ofoxygen. The time course of 14C-incorporation into photosyntheticproducts showed that 3-phosphoglycerate was the initial productof photosynthetic CO2 fixation in Chroomonas sp. cells. During5-min photosynthesis, a considerable amount of 14C was incorporatedinto the insoluble fraction (mostly cryptomonad starch), andoxygen predominantly affected 14C-incorporation into this fraction.Although 14C-incorporation into intermediates of the photorespiratorypathway increased with increasing O2 concentration, the amountswere much less than expected from the degree of oxygen inhibition.It is noteworthy that 14C-dihydroxyacetone phosphate accumulatedduring photosynthesis only under the anaerobic condition, whereasthe levels of the other phosphate esters were scarcely affectedby the oxygen concentration. Ribulose-1,5-bisphosphate carboxylase from Chroomonas sp. wascompetitively inhibited by oxygen, and its Km(CO2) value wassimilar to those of terrestrial C3 plant enzymes. (Received November 19, 1984; Accepted May 20, 1985) 相似文献
3.
Oxygen enhanced photosynthetic 14CO2 fixation in Anacystis nidulanscells. Results obtained under different conditions revealedthe following properties of the oxygen enhancement:
- The enhancement was most significant at ca. 10% O2. Furtherincrease in oxygen concentration decreased the enhancing effect.The rate under 100% O2 was equivalent to or a little higherthan that under N2 gas.
- b) With the increase in CO2 concentration,the magnitude ofthe enhancing effect decreased. No oxygen enhancementwas observedwhen the CO2 concentration. was raised to 9,000ppm.
- c) The enhancement was observed only at high light intensities.No enhancement was observed when the rate of photosynthesiswas limited by light intensity.
- Ribulose 1,5-diphosphate (RuDP)carboxylase activity was demonstratedin the extract obtainedfrom A. nidulans cells. We also foundthat the RuDP carboxylaseactivity in this extract was competitivelyinhibited by oxygen.
- Based on the above-mentioned results, the possible mechanismunderlying the observed enhancing effect of oxygen was discussed.
4.
Photosynthetic CO2 fixation was studied using cells of Rhodospirillumrubrum grown heterotrophically on malate or butyrate. Ratesof CO2 fixation were higher in the malategrown cells than inthe butyrate-grown bacteria but ribulosebisphosphate (RUP2)carboxylase/oxygenase activities were higher in the extractsprepared from the butyrate-grown bacteria. The photosyntheticCO2 fixation in the butyrate-grown R. rubrum cells was inhibitedby KCN, and the inhibitory effect of O2 on CO2 fixation wasreversed when cells were returned to an N2 atmosphere. In themalate-grown cells, photosynthetic CO2 fixation was insensitiveto KCN and the inhibitory effect exerted by O2 was practicallyirreversible. 14CO2 was not incorporated into glycolate by either malate-or butyrate-grown cells in an N2 atmosphere, but small amountsof labeled glycolate were found in malate- and butyrate-growncells in air or 100% O2. Glycolate excreted by these cells in100% O2 was measured colorimetrically and its identity establishedby mass spectrometry. When the O2 atmosphere was labeled with18O2, only one of the carboxyl oxygens of the excreted glycolatewas labeled, and the enrichment of 18O in this carboxyl oxygenrelative to the 18O2 provided was greater than 80%. These studiesshow that significant glycolate production by R. rubrum onlyoccurs in the presence of O2 and that in both malateand butyrate-growncells, the glycolate so formed is presumably produced via RuP2oxygenase.
1 Paper No. 46 in the series "Structure and Function of ChloroplastProteins", and research supported in part by research grantsfrom the Japanese Ministry of Education (No. 211113), the TorayScience Foundation (Tokyo), and the Nissan Science Foundation(Tokyo). (Received August 19, 1978; ) 相似文献
5.
Methionine sulfoximine (MSO) greatly reduced the carbon dioxideexchange rate (CER) of detached wheat (Triticum aestivvm L.cv Roland) leaves in 21% O2, but only slightly reduced it in2% O2. A supply of 50 mM NH4Cl had little effect on the CERirrespective of the O2 concentration. A simultaneous additionof glutamine and MSO protected against the inhibition of photosynthesisto a considerable extent and caused the accumulation of moreNH3 than did the addition of MSO alone. Fixation of 14CO2 in wheat leaves was inhibited by MSO treatmentin 22% O2, 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 14CO2 fixation pattern. NH4Cl stimulatedthe synthesis of amino acids from 14CO2, especially the synthesisof serine in 22% O2. Our observations show that factors other than the uncouplingof photophosphorylation by accumulated NH3 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
6.
The reductive carboxylic acid cycle appears to be the majorcarbon assimilation pathway in green sulfur bacteria, Chlorobiumthiosulfatophilum. While cyanide was relatively ineffectivein inhibiting the bacterial photosynthetic CO2 fixation, photosynthesiswas strongly impaired in an O2-containing atmospheric environment.No glycolate formation was detected in Chlorobium under an O2atmosphere. In the purple sulfur bacteria, Chromatium vinosum,however, photosynthesis was highly sensitive to cyanide, andin a short-term incubation (up to 10 min) photosynthetic CO2fixation was found to be relatively indifferent to an O2-containingatmosphere of up to 100% O2. Significant formation of glycolatewas demonstrated upon a very brief exposure to O2, whereas thetotal photosynthetic CO2 fixation was slightly affected. However,ribulose-1,5-bisphosphate carboxylase activity in Chromatiumextract was competitively inhibited by O2 in a similar mannerto the higher plant enzyme, K1(O2) value being 0.7 mM at pH8.2. The percentage of incorporation of 14CO2 into glycolateand glycine under an O2-containing atmosphere declined withincreasing levels of bicarbonate concentrations in the medium.The Warburg effect and biosynthetic mechanisms involving glycolatein photosynthetic bacteria are discussed.
1 This is paper XXXIX in the series "Structure and Functionof Chloroplast Proteins". Paper XXXVIII is reference (6) Asamiand Akazawa (1977). This research was supported in part by grantsfrom the Ministry of Education of Japan (111912), the TorayScience Foundation (Tokyo), and the Japan Securities ScholarshipFoundation (Tokyo). (Received January 28, 1977; ) 相似文献
7.
A study has been made of photosynthetic 14CO2 fixation by isolatedmature internodes of Nitella translucens. Experimentalconditions were similar to those used in studies of the ionicrelations of these cells. Maximum rates of photosynthesis were3340µµmoles CO2, fixed per cm2 of surfacearea per second (equivalent to 1215 /xmoles fixed permg chlorophyll per hour). l4CO2 fixation was inhibited to thedark level by 3(3,4,dichlorophenyl)-1, 1-dimethylurea (at 0-6µM or 10µM) and by the uncoupler carbonyl cyanide-m-chlorophenylhydrazone(SµM). The presence of imidazole or ammonium sulphate(both of which uncouple ATP production in vitro) did not resultin an inhibition of 14CO2 fixation. These results are discussedin relation to published work on solute uptake by Nitella translucens.During photosynthesis there was rapid movement of 14C-labelledorganic compounds out of the chloroplasts. 14C-labelled sucrose,ammo-acids, and sugar phosphates were found in samples of vacuolarsap. 相似文献
8.
Exposure to atmospheric conditions which promote photorespirationstrongly inhibits photosynthesis in a mutant of Arabidopsislacking mitochondrial serine transhydroxymethylase activity,and glycine accumulates as a stable end-product of photorespiratorycarbon and nitrogen flow. By providing exogenous serine andammonia to leaves of the mutant, wild-type photosynthesis ratescan be temporarily maintained in the absence of photorespiratoryCO2 evolution. In these circumstances, the rate of glycine accumulationprovides a direct measure of photorespiratory flux which isnot complicated by the efflux and refixation of photorespiredCO2, the dilution of radioactive label by endogenous metabolicpools, or non-specific effects of metabolic inhibitors. At thestandard atmospheric concentration of CO2, the rate of glycineaccumulation in the mutant was proportional to the oxygen concentration,amounting to 53% of the rate of gross CO2-fixation at 21% O2.At normal levels of O2, glycine accumulation was maximal atabout 475 µl CO211 and was reduced at higher orlower CO2 concentrations, being almost abolished at 3000µ1CO211. These observations are discussed in the contextof a model of photorespiration based on the properties of ribulose1, 5-bisphosphate carboxylase/oxygenase, and in relation tothe results of previous attempts to measure photorespiration.Preliminary evidence from 14CO2-labelling experiments whichsuggests a non-photorespiratory pathway of serine synthesisis also presented. Key words: Arabidopsis mutant, Photorespiration, Serine transhydroxymethylase 相似文献
9.
The rate of net CO2 fixation in Lemna gibba L. was decreasedto 50% by 100150 min incubation in the presence of 05mol m3 L-methionine-D,L-Sulphoximine (MSO), an irreversibleinhibitor of glutasnine synthetase (GS). The pattern of inhibitionwas similar in both 21% O2 and 2% O2. The inhibition was accompaniedby increased intracellular levels. Incubation with 10 mol m3 under the same conditions, but without MSO, resulted in even higher levels but the rate of CO2 fixation was unaffected. Additions of glutamine, glutamate, glycine or serine delayedthe MSO-induced inhibition of CO2 fixation. The same amino acidsdelayed the inactivation of GS by MSO. Thus inhibition of CO2 fixation by MSO in Lemna is neither causedby elevated levels nor closely related to photorespiration. Possibly, MSO causes shortage of amino-N formaintenance of the functional integrity of the photosyntheticapparatus. Key words: Methionine sulphoximine, CO2, fixation, Lemna 相似文献
10.
Ammonia Induces Starch Degradation in Chlorella Cells 总被引:3,自引:0,他引:3
When ammonia was added to cells of Chlorella which had fixed14CO2 photo synthetically, 14C which had been incorporated intostarch was greatly decreased. A similar effect was observedwhen potassium nitrate and sodium nitrite were added. The ammonia-induceddecrease in 14C-starch was observed in all species of Chlorellatested. With cells of C. vulgaris 11h, most of the radioactivityin starch was recovered in sucrose, indicating that ammoniainduces the conversion of starch into sucrose. The percent of14C recovered in sucrose differed from species to species andpractically no recovery in sucrose was observed in C. pyrenoidosa.In most species tested, the enhancing effects of blue lightand ammonia on O2 uptake as well as the ammonia effect on starchdegradation were greater in cells which had been starved inphosphate medium in the dark than in non-starved cells. In contrast,the enhancing effect of ammonia on dark CO2 fixation was muchgreater in non-starved cells. C. pyrenoidosa was unique in thatblue light did not show any effect on its O2 uptake. (Received August 15, 1984; Accepted November 16, 1984) 相似文献
11.
The influence of hydrogenase in Bradyrizobum-Phaseoleae symbioseswas studied ex-planta and in-planra in soybean (Glycine max)and cowpea (Vigna unguiculata). The hydrogenase was activatedby the addition of hydrogen in the incubation gas phase whichmodified the response of nitrogenase activity of Hup+ (hydrogenuptake positive) symbiosis to the external oxygen partial pressure.For bacteroids the hydrogenase expression increased nitrogenaseactivity at supraoptimal pO2, acting possibly as a respiratoryprotection of nitrogenase. However, at suboptimal pO2, nitrogenaseactivity of Hup+ bacteroids decreased with hydrogen, a phenomenonattributed to the lower efficiency of ATP synthesis from hydrogenthan from carbon substrates oxidation. For undisturbed nodules,the hydrogenase expression in soybean increased the optimalpO2 for ARA (COP), from 35.3 to 40.3 kPa O2, and the ARA atsupraoptimal pO2; at suboptimal PO2 there was a negative effectof hydrogenase on ARA, although this inhibition was less thanon bacteroids and was not detected if plants were grown at 15°C rather than 20 °C root temperature. No H2 effectwas detected on cowpea nodules. The results on soybean nodulesare consistent with the concept that symbiotic nitrogen fixationis oxygen-limited and that hydrogenase activity has no beneficialeffect on nitrogen fixation in O2 limitation. Key words: Glycine max, hydrogenase, nitrogenase, nitrogen fixation, nodules, Vigna unguiculata 相似文献
12.
Accumulation and Utilization of Dissolved Inorganic Carbon by a Marine Unicellular Coccolithophorid, Emiliania huxleyi 总被引:1,自引:0,他引:1
The mechanism for utilization of dissolved inorganic carbon(DIC) was investigated in the marine unicellular calcareousalga Emiliania huxleyi, grown with constant aeration. The apparentK0.5 (DIC), the concentration of DIC which attains one-halfof the maximum velocity of apparent photosynthesis, for photosyntheticevolution of O2, measured under saturating light, was 5.5 mM(55 µM for CO2) at pH 8.0 and 25°C. The value of K0.5was not affected by inhibitors of carbonic anhydrase (CA), andan electrometric assay of CA showed that the enzyme was notinvolved in photosynthesis in this alga. The rate of photosyntheticfixation of 14C-DIC into acid-stable products was about 20 timeshigher than that into CaCO3, irrespective of the external concentrationof DIC. In short-term experiments, 14C-DIC was usually incorporatedinto the internal pool of DIC (IIC) to concentrations up to13 to 16 times higher than that of the external DIC. CO2 addedexternally was utilized mainly for fixation of CO2 and accumulationof IIC. By contrast, HCO-3 was utilized mainly for productionof CaCO3 and accumulation of IIC. Incorporation of 14C intoIIC was partially suppressed by DCMU or in darkness but itstransfer to CaCO3 was unaffected. These results suggest thataccumulation of IIC in this alga, even under ordinary circumstances,is only partially responsible for increasing the efficiencyof utilization of DIC by photosynthetic fixation but may bemost useful for the production of CaCO3. (Hydroxyethylidene) bisphosphonic acid, an inhibitor of thegrowth of CaCO3 crystals, completely suppressed production ofCaCO3. The accumulation of IIC was also partially suppressed,but photosynthetic fixation of CO2 was enhanced. In a pulse-chaseexperiment with 14CDIC, 14C incorporated into IIC and CaCO3in darkness was transferred to acid-stable products of photosynthesisin the light. These results suggest that 14C-DIC in IIC andpre-formed CaCO3 may be useful sources of carbon for fixationof CO2. (Received July 2, 1993; Accepted January 10, 1994) 相似文献
13.
Chlorella vulgaris 11h cells grown in air enriched with 4% CO2(high-CO2 cells) had carbonic anhydrase (CA) activity whichwas 20 to 90 times lower than that of algal cells grown in ordinaryair (containing 0.04% CO2, low-CO2 cells). The CO2 concentrationduring growth did not affect either ribulose 1,5-bisphosphate(RuBP) carboxylase activity or its Km for CO2. When high-CO2 cells were transferred to low CO2 conditions,CA activity increased without a lag period, and this increasewas accompanied by an increase in the rate of photosynthetic14CO2 fixation under 14CO2-limiting conditions. On the otherhand, CA activity as well as the rate of photosynthetic 14CO2fixation at low 14CO2 concentrations decreased when low-CO2cells were transferred to high CO2 conditions. Diamox, an inhibitor of CA, at 0.1 mM did not affect photosynthesisof low-CO2 cells at high CO2 concentration (0.5%). Diamox inhibitedphotosynthesis only under low CO2 concentrations, and the lowerthe CO2 concentration, the greater was the inhibition. Consequently,the CO2 concentration at which the rate of photosynthesis attainedone-half its maximum rate (Km) greatly increased in the presenceof this inhibitor. When CO2 concentration was higher than 1%, the photosyntheticrate in low-CO2 cells decreased, while that in high-CO2 cellsincreased. Fractionation of the low-CO2 cells in non-aqueous medium bydensity showed that CA was fractionated in a manner similarto the distribution of chlorophyll and RuBP carboxylase. These observations indicate that CA enhances photosynthesisunder CO2-limiting conditions, but inhibits it at CO2 concentrationshigher than a certain level. The mechanism underlying the aboveregulatory functions of CA is discussed.
1This work was reported at the International Symposium on PhotosyntheticCO2-Assimilation and Photorespiration, Sofia, August, 1977 (18).Requests for reprints should be addressed to S. Miyachi, RadioisotopeCentre, University of Tokyo, Bunkyo-ku, Tokyo 113, Japan. (Received December 11, 1978; ) 相似文献
14.
Dwarf french beans (Phaseolus vulgaris var. Canadian Wonder)were grown in chambers at 25?C with the roots aerated at 20per cent oxygen and tops variously maintained at: T1 O2 0.21;CO2 270?106: T2; O2 0.05, CO2, CO2 270?106: T3;O2 0.21; CO2 550?106. Experiment 1 (T1 and T2) lasted2 weeks: Experiment 2 (T1 T2 and T3) only one week. Hourly estimatesof CO2 uptake were made by gas analysis and weekly estimatesof fresh weight, dry matter in tops and roots, and leaf area,by sampling. Light intensity was 80 W m2 of photosyntheticallyactive radiation. An attempt was made to explain the results in terms of a simplelight absorption model such that
where dV/dt is the rate of CO2 uptake per plant, ßis the photosynthetic efficiency, I0 is the incident light intensity,f is the fraction of incident light absorbed by unit leaf layerand L is the leaf area index. The analysis showed that ß(T2)was at least double ß(T1), whilst f(T2) was smallerthan f(T1) at a given leaf area. The results also required thatthroughout the period of the experiment, fL(T1)=fL(T2) at anygiven time, i.e. the treatment with the larger leaf area (T2)has the smaller value of f, and therefore intercepts less lightper unit leaf area. This could be advantageous for plant growth,but requires further experiments. The photosynthetic rates per unit leaf are about 40 per centgreater in T2 than T1. Over the relatively short period of the experiment the resultsare adequately described by U=btn, where U is the accumulatedcarbon dioxide uptake, b is related to the photosynthetic efficiency(different for the differing treatments), and n is a constant(similar for all treatments). This relationship with time isbelieved to be a relationship with accumulated radiation, forthe light was constant throughout the experiments. Comparisons of carbon fixed (measured gas uptake) and dry matteraccumulation (sampling) show great scatter with an average valueof 0.43. The first week's results were generally smaller thanthis value and the second week's greater. Energy fixation as a fraction of photosynthetically active radiationon the ground area covered by the plants ranged from 3.5 to10 per cent. The results from treatment T3 were similar to T2 suggestingthat increasing CO2 concentration decreases the growth inhibitionat 21 per cent O2. 相似文献
15.
Biochemical studies of epidermal tissue may not reflect metabolismof the guard cells which represent less than 5% of the tissuevolume. Pure samples of guard cell protoplasts of Commelinacommunis were therefore used to investigate CO2 fixation ratesand 14C-labelling patterns of metabolites in the light and thedark. Qualitatively, results were similar in most respects tothose obtained in a previous study (Schnabl, 1980) for guardcell protoplasts of Vicia faba. CO2 fixation rates by guardcell protoplasts of C. communis were the same in the light andthe dark but about 50 times lower than the values Schnabl obtainedfor V.faba. The 14C-labelling pattern of metabolites in C. communiswas also similar in the light and the dark: over 60% of thetotal fixed was in malate with only 1% in sugar phosphates.Label was also detected in starch, aspartate, glutamate andcitrate but not in glycollate as previously recorded in V. fabaguard cell protoplasts. The results confirm the view that the reductive pentose phosphatepathway does not occur in guard cells of C. communis. Key words: CO2 fixation, Guard cell protoplasts, Stomata 相似文献
16.
The nature of the lack of oxygen inhibition of C3-photosynthesisat low temperature was investigated in white clover (Trifoliumrepens L.). Detached leaves were brought to steady-state photosynthesisin air (34 Pa p(CO2), 21 kPa p(O2), balance N2) at temperaturesof 20°C and 8°C, respectively. Net photosynthesis, ribulose1,5-bisphosphate (RuBP) and ATP contents, and ribulose 1,5-bisphosphatecarboxylase/oxygenase (RuBPCO) activities were followed beforeand after changing to 2·0 kPa p(O2). At 20°C, lowering p(O2) increased net photosynthesis by37%. This increase corresponded closely with the increase expectedfrom the effect on the kinetic properties of RuBPCO. Conversely,at 8°C net photosynthesis rapidly decreased following adecrease in p(O2) and then increased again reaching a steady-statelevel which was only 7% higher than at 21 kPa p(O2). The steady-staterates of RuBP and associated ATP consumption were both estimatedto have decreased. ATP and RuBP contents decreased by 18% and33% respectively, immediately after the change in p(O2) suggestingthat RuBP regeneration was reduced at low p(O2) due to reducedphotophosphorylation. Subsequently, RuBP content increased again.Steady-state RuBP content at 2·0 kPa p(O2) was 24% higherthan at 21 kPa p(O2). RuBPCO activity decreased by 22%, indicatingcontrol of steady-state RuBP consumption by RuBPCO activity. It is suggested that lack of oxygen inhibition of photosynthesisat low temperature is due to decreased photophosphorylationat low temperature and low p(O2). This may be due to assimilateaccumulation within the chloroplasts. Decreased photophosphorylationseems to decrease RuBP synthesis and RuBPCO activity, possiblydue to an acidification of the chloroplast stroma. Key words: Oxygen inhibition, photosynthesis, ribulose bisphosphate carboxylase/oxygenase 相似文献
17.
Etiolated Avena sativa L. coleoptile sections were used to determinethe influence of C2H4 on in vivo and in vitro rates of CO2 fixation,and to measure the influence of various permutations of C2H4,CO2, and malate on growth. Whereas 1 mM malate or 320 µI-1 CO2 stimulated growth by approximately 100 per cent, inhibitionof growth by 10-8 µ I-1 C2H4 was substantial only in thepresence of malate or CO2 The increase in growth rate in responseto these two agents was eliminated by the simultaneous applicationof C2H4. The in vivo rate of dark [14C]bicarbonate fixationand in vitro enzymic assays of fixation were not measurablyinhibited by C2H4. These results are discussed in the lightof evidence which indicates that CO2-stimulated growth is mediatedby dark fixation. The data do not support the view that C2H4inhibition of growth results from an inhibition of fixation,but suggests that C2H4 may inhibit some step in the processby which malate stimulates growth. 相似文献
18.
Atwell, B. J. and Greenway, H. 1987. Carbohydrate metabolismof rice seedlings grown in oxygen deficient solution.J.exp. Bot. 38: 466478. Rice seedlings (Oryza sativa L.) were grown in the dark forup to 4 d in solutions containing various concentrations ofO2. The rate of depletion of the endosperm was most rapid inaerated solution (0·25 mol O2 m3), largely dueto the inhibition of growth of seedlings at very low O2 concentrations.Earlier suggestions that there is a deficit of sugars for growthand energy generation in O2 deficient coleoptiles were tested. Coleoptiles, shaking in aerated solution, respired about one-thirdof the endogenous sugars to CO2 and incorporated the rest intostructural compounds. In contrast, the proportion of carbonwhich went to growth in anoxia was very low. Consistent withthese results, endogenous sugar levels were generally highestat low O2 concentrations. Even so, coleoptiles grown and testedas low as 0·03 mol O2 m3 showed appreciable metabolismof exogenous 14C-glucose to CO2, soluble and insoluble compounds,suggesting that a minimal O2 supply was sufficient to sustainsome growth. Furthermore, glucose feeding caused little or norise in O2 uptake or tissue sugar levels. Similarly, the specificactivity of the evolved CO2 was not markedly different in coleoptilesgrowing at 0·03 and 0·25 mol O2 m3 Further evidence was obtained to show that endogenous substrateswere adequate for growth and respiration at both low and highO2 concentrations. Exogenous glucose and malate did not stimulateO2 uptake at any stage of growth in aerated coleoptiles. Therewas sufficient endogenous substrate to sustain a 3545%rise in O2 uptake induced by uncoupling and enrichment withO2. Exogenous glucose did not stimulate growth of intact seedlingsat any O2 concentration. Key words: Rice seedlings, carbohydrate metabolism, oxygen deficient solution 相似文献
19.
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
20.
Inorganic carbon transport during photosynthesis of cyanobacteriumAnabaena variabilis grown under ordinary air was investigatedby supplying 14CO2 or H14CO3 solution to three differentstrains. Both CO2 and HCO3 were accumulated within thealgal cells. In the cell suspension from which dissolved inorganiccarbon had been depleted by pre-illumination, CO2 was transportedand accumulated faster than HCO3. When the concentrationof HCO3 injected into the cell suspension of A. variabilisM3 was 25 times as high as that of CO2 (the expected ratio atequilibrium at pH 7.8), the initial rates of fixation of bothinorganic carbon species were practically the same. On the otherhand, when 14CO2 or H14CO3 was added under steady statephotosynthetic conditions, both carbon species were transportedat similar rates. The ratio of fixed to transported carbon measuredafter the initial 5 s was only 2327% regardless of thecarbon species supplied. This percentage is much lower thanthat reported for Chlorella cells.
1 To whom reprint requests should be addressed (Received June 30, 1986; Accepted December 16, 1986) 相似文献