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1.
Dark-grown cotyledons of pine (Pinus thunbergit) did not exhibitO2 evolution, but this capability was rapidly activated by illuminationfor a short period (photoactivation). To examine the biochemicalchanges which accompany the process of photoactivation in gymnosperms,a method enabling the preparation of highly active O2-evolvingphotosystem II (PS II) membranes was applied to light-grown,dark-grown, and photoactivated cotyledons. PS II membranes preparedfrom light-grown cotyledons exhibited high O2-evolving activity,and contained all the intrinsic proteins as well as the threeextrinsic proteins (32, 23 and 17 kDa) associated with PS II.These membranes were also found to contain 4.4 Mn and 0.83 Ca/PSII reaction center. PS II membranes from dark-grown cotyledonscontained all the intrinsic proteins, but preserved only 32kDa extrinsic protein, and zero Mn and 0.85 Ca/PS II reactioncenter. The two extrinsic proteins (23 and 17 kDa) absent inthe PS II membranes from dark-grown cotyledons were, however,present as mature forms in whole thylakoid membranes from thecorresponding sample. The PS II membranes isolated from photoactivatedcotyledons showed a high activity of O2 evolution and retainedthe three extrinsic proteins, 5.3 Mn and 1.1 Ca/PS II reactioncenter, respectively. The results indicated that Mn and thetwo extrinsic proteins were tightly integrated in the O2-evolvingapparatusduring the process of photoactivation but integration of Capreceded the integration of Mn by photoactivation. (Received December 9, 1991; Accepted February 1, 1992)  相似文献   

2.
Relative optical cross sections for flash-induced O2- and N2-productionwith water and 1 mM NH2OH as electron donors to PSII, respectively,as well as that for PSI-mediated O2-uptake have been measuredin tobacco chloroplasts by mass spectrometry. In the wild typetobacco these three reactions are driven by three populationsof photosynthetic units different with respect to the antennasize. The antenna size of O2-evolving units is twice as largecompared to the N2-evolving one, but both of these have thesame spectral characteristics in the far red region. In contrastto the wild type, the antenna sizes of O2- and N2-evolving unitsin the chlorophyll b-deficient tobacco mutant Su/su var. Aureaare the same as the sizes of the N2-evolying units in the wildtype chloroplasts. Taking into account the data of Thielen andVan Gorkom [Biochim. Biophys. Acta (1981) 635:111] on a strongdifference in the relative amounts of PSIIß and PSIIßin the mutant compared with the wild type (the ratio about 1: 3 and 3 : 1 , respectively) it is concluded that mainly thestroma-exposed PSIIß units are competent to N2-evolution. (Received November 11, 1993; Accepted April 25, 1994)  相似文献   

3.
The inhibitory effects of sulfite ions on zeatin-induced cellexpansion in cotyledons excised from dark-grown seedlings ofcucumber (Cucumis sativus L.) were examined. With 50 µMzeatin the growth rate in white light was about twice that ofthe control. Addition of Na2SO3 in the growth medium inhibitedthe zeatin-induced growth of cotyledons. Zeatin-treatment increasedthe osmotic potential in cell sap of cotyledons, while sulfitedecreased it. These treatments had no significant effect onpotassium concentration. Sulfite inhibited the zeatin-inducedincrease in contents of fructose and glucose, but did not affectsucrose content. The relative contents of non-cellulosic constituentsof cell walls fell with the advance of culture. This decreasewas repressed by sulfite, indicating that inhibition of expansiongrowth in cucumber cotyledons by sulfite ions was the resultof alterations in the cell wall structure due to changes inthe cell wall metabolism. (Received June 12, 1984; Accepted October 24, 1984)  相似文献   

4.
Three-day-old dark-grown soybean [Glycine max (L.) Merr.] seedlingswere transferred to 2 mM CaSO4 or 10–5 M dimethipin in2 nM CaSO4 and root-fed via liquid culture. Plants were placedin continuous darkness or in continuous white light (200 µE.m–2?s–11,PAR) at 25?C. Dimethipin inhibited root and shoot elongationin dark-grown plants after 24 h and 48 h, respectively. In thelight, root elongation was inhibited also after 24 h, but hypocotylelongation was not significantly affected. Extractable phenylalanineammonia-lyase (PAL) activity per axis in dimethipin-treateddark-grown axes was not generally affected but, in the lightdimethipin caused a significant decrease in PAL activity (24to 96 h). Total soluble hydroxyphenolics in axes were not affectedby dimethipin in light- or dark-grown plants. Anthocyanin andchlorophyll levels were lowered in hypocotyls of dimethipin-treatedplants after 48 to 96 h. Soluble protein in hypocotyls of light-or dark-grown seedlings was not substantially affected by dimethipin.Nitrate reductase (NR) activity (per organ) was generally notaffected by dimethipin in light-grown cotyledons, but in theroots of these seedlings, NR activity was significantly decreased.Proteolytic enzyme activity using three substrates (leucine-p-nitroanilide,LPNA; proline-p-nitroanilide, PPNA; and benzoylarginine-p-nitroanilide,BAPA) indicated little effect on enzyme activities per organin roots and hypocotyls. These data suggest that dimethipinat low concentrations can cause significant growth inhibitionin soybean seedlings grown in either light or darkness and thatfurthermore, extractable activities of some enzymes associatedwith nitrogen metabolism and secondary metabolism are alteredby this chemical. Light also plays a role in the activity ofthis chemical. (Received November 29, 1983; Accepted January 25, 1984)  相似文献   

5.
The stay-green mutations cytG and Gd1d2 prevent the normal yellowingduring senescence of soybean (Glycine max) leaves and cotyledons.Because light plays such an important role in regulating morphogenesisand it promotes the formation of chlorophyll (Chl), we determinedthe effect of cytG and Gd1d2 (in a cv. Clark background) onthe development and some light responses of seedlings. AlthoughcytG and Gd1d2 seeds, particularly the cotyledons, are greenwhen mature, 44 and 71 % respectively of this Chl broke downwhen the seeds were germinated in darkness. Chlorophyllidesand phaeophytins were not present in the seeds in significantamounts. cytG and Gd1d2 as well as wild type (cv. Clark) seedlingsdeveloped a full etiolation syndrome (morphology and lack ofChl) in darkness. Light induced rapid Chl accumulation in thedark-grown seedlings with no apparent difference among the threeisolines. A short (8 h) exposure to light induced some Chl inthe cotyledons of dark-grown plants, and 22 h of light producedfour times more. Following return to darkness, the 8-h groupshowed very little breakdown over the next 12 d. After the 22-hgroup was returned to darkness, the wild-type lost Chl steadily,but Gd1d2 and eventually also cytG inhibited this breakdown.In the 22-h group, the Chl a/b ratio decreased in wild typeand cytG indicating preferential breakdown of Chl a relativeto Chl b; however, Gd1d2 prevented this change. cytG and Gd1d2seem to act preferentially on Chl breakdown rather than synthesis.Copyright1995, 1999 Academic Press Glycine max, soybean, chlorophyll, chlorophyll a/b ratio, cotyledons, etiolation, cytG, Gd1d2, mutations, senescence  相似文献   

6.
During photoreactivation of the O2-evolving center in Tris-inactivated/Mn-depletedthylakoids, a slow O2-consumption occurred. This O2-consumptionbecame detectable when the O2-evolving activity of thylakoidswas inactivated by Tris-treatment and decreased as photoreactivationproceeded. The O2-consumption and photoreactivation similarlyrequired Mn2+ at µM levels in addition to PSII electrondonors and shared severa common characteristics. Stimulationof O2-consumption and photoreactivation by these cofactors werealways accompanied by enhancement in chlorophyll fluorescenceinduction, suggesting the involvement of a Mehler-type reactionin photoreactivation. Although the electron transport due tothis O2-consumption was rapid enough to oxidize 4 Mn2+ ionsto reconstitute the tetranuclear Mn-cluster in each O2-evolvingcenter in a few seconds, actual recovery of O2-evolving activityoccurred more slowly in a few minutes. It was inferred thatphotoreactivation in Tris-inactivated thylakoids is not a simplephotooxidation of Mn22+ but involves more complicated processeswhich are coupled to the Mehlertype electron transport fromPSII to oxygen via PSI. (Received July 11, 1994; Accepted August 23, 1996)  相似文献   

7.
Nitrogen dioxide (NO2) fumigation inhibited nitrate reductase(NR, EC 1.6.6.1 [EC] ) activity assayed by an in vivo system in thecotyledons, but not in the first leaves, of squash (Cucurbitamaxima Duch.) seedlings. The inhibition was recovered when theseedlings were transferred to NO2-free conditions, indicatingthat the effect of NO2 was reversible. The NADH content in thecotyledons, photosynthetic O2 evolution and respiratory O2 uptakedid not change notably under NO2 fumigation. Nitrate contentsin the cotyledons and first leaves did not change with NO2 fumigation,but nitrite, ammonium and rapidly-metabolized amino acids contentsincreased. The inhibitory effect of NO2 was also observed inthe in vitro assay, though the inhibition rate was smaller thanthat in the in vivo assay. These results indicate that the inhibitoryeffect of NO2 on NR activity in squash cotyledons was derivedin part from the decrease in the amount of active NR due toammonium and/or amino acids accumulated in the tissue underNO2 fumigation. (Received February 12, 1985; Accepted May 27, 1985)  相似文献   

8.
Time-courses of 14CO2-fixation and of enzyme activities involvedin photorespiration and photosynthesis were determined duringthe life span of cotyledons from sunflower seedlings (Helianthusannuus L.). Glycolate formation in vivo was estimated from theresults of combined labelling and inhibitor experiments. NADPH-glyceraldehyde-3-phosphatedehydrogenase, NADPH-glyoxylate reductase and chlorophyll werewell correlated with the time-course of 14CO2-fixation (photosynthesis).There was, however, a considerable discrepancy between the developmentalsequence of photosynthesis and that of both ribulose-l,5-bisphosphatecarboxylase and glycolate oxidase. Furthermore, time-coursesof glycolate oxidase activity in vitro and of glycolate formationin vivo differed significantly. Therefore, the use of glycolateoxidase as a marker for the activity of photorespiration ingreening sunflower cotyledons may be questionable. Results from14CO2-labelling experiments with cotyledons treated with theglycolate oxidase inhibitor 2-hydroxy butynoic acid suggestthat glycolate formation relative to CO2-fixation is reducedin senescent cotyledons. Key words: Development, glycolate oxidase, photorespiration, ribulose-l,5-bisphosphate carboxylase, oxygenase  相似文献   

9.
In starchy cotyledons of Vigna cylindrica (L.) Skeels (Mitorisasage)during seed germination, the enzymes of the glyoxylate cyclewere located in the matrix of mitochondria. Glyoxysomes wereabsent. The glyoxylate cycle in the mitochondria supplies organicacids to the tricarboxylic acid cycle. In mitochondria, isocitratelyase activity was much higher than malate synthase activity.Part of the glyoxylate thus produced in mitochondria may benonenzymatically converted to formate by H2O2 and the formatethen converted to CO2 by peroxidase or by formic dehydrogenase.The activity of superoxide dismutase, which supplies H2O2, washigher in mitochondria than in peroxisomes. The remaining glyoxylatein mitochondria is possibly converted to glycine by alanine-glyoxylateaminotransferase or transported to peroxisomes which lackedisocitrate lyase activity but had high malate synthase activity.In peroxisomes, glyoxylate may be also produced from urate,as is suggested by the fairly high activities of uricase, allantoinaseand allantoicase. Judging from the enzyme distribution, Vignaperoxisomes should be capable of producing malate, oxalacetate,citrate, isocitrate and a-ketoglutarate. 1Present address: Department of Horticulture, College of Agricultureand Animal Science, Yeugnam University, Gyeongsan 632, Korea. (Received May 27, 1987; Accepted October 7, 1987)  相似文献   

10.
The effects of light on denitrifying activity during growthwere studied in an aerobic photosynthetic bacterium, Roseobacterdenitrificans (formerly Erythrobacter sp. OCh 114). When aerobicallygrown cells were transferred to anaerobic conditions in thepresence of nitrate, this bacterium exhibited denitrifying activity,with either succinate or malate serving as an electron donorin addition to endogenous substrates. The final product of denitrificationwas identified as nitrous oxide (N2O), a result that confirmsthe presence of nitrate and nitrite reductases, but not N2Oreductase, in these cells. Illumination during aerobic growthcaused a marked enhancement of the denitrifying activity. Theactivity increased with increasing intensity of light up to40 mW cm–2 and was over 20 times that in dark-grown cells.Enhancement of denitrifying activity in illuminated cells wasclosely related to increases in levels of components that areinvolved in the denitrifying pathway, namely, nitrate and nitritereductases. Development of a denitrifying system under aerobicconditions and the enhancement of denitrifying ability by lightin Roseobacter denitrificans are unique characteristics, unlikethose of other known denitrifying bacteria. (Received October 29, 1990; Accepted January 17, 1991)  相似文献   

11.
Four 13-hydroxygibberellins, gibberellin A1 (GA1), 3-epi-GA1,GA19 and GA20 were identified by full-scan GC/MS in extractsof lettuce seedlings (Lactuca sativa L. cv. Grand Rapids). Theresults suggest that the early-13-hydroxylation biosyntheticpathway to GA1 functions in the lettuce seedlings. It was alsofound that GA1 is active per se in the control of hypocotylelongation in lettuce seedlings. To investigate the relationshipbetween control by light of hypocotyl elongation and levelsof endogenous GAs in lettuce, endogenous levels of GAs werequantified by radioimmunoassay in seedlings that had been grownfor 5 days in the dark (5D) and in those that had been grownfor 4 days in the dark and then under white light for 1 day(4D1L). The endogenous level of GA1 in the upper and lower partsof hypocotyls in 5D seedlings was about four times higher thanthat in 4D1L seedlings. The response of explants (hypocotylsegments with cotyledons) from dark-grown seedlings to GA1 isknown to be similar in the dark and under white light when theexplants are treated with inhibitors of the biosynthesis ofGA. Therefore, the above information suggests that the highlevel of GA1 in hypocotyls of dark-grown seedlings is responsiblefor the rapid elongation of hypocotyl, while irradiation bywhite light decreases the endogenous level of GA1 in the hypocotylswith a resultant decrease in the rate of hypocotyl elongation. (Received March 13, 1992; Accepted May 21, 1992)  相似文献   

12.
Endopeptidase (azocaseolytic enzyme) and carboxypeptidase activitiesin cotyledons of germinating Vigna mungo seeds increased until3 days after the onset of imbibition and decreased thereafter.In detached and incubated cotyledons, the endopeptidase activityincreased only a little while the carboxypeptidase activitycontinued increasing even after 3 days of incubation. The activitiesof leucine-aminopeptidase and alanine-aminopeptidase, exceptfor that of one leucine-aminopeptidase isoenzyme relativelyabundantly present in unimbibed dry cotyledons, increased slightlyon the first day and declined during germination. In detachedcotyledons, the activities maintained their initial levels throughoutthe incubation period. When cotyledons were detached from germinatingseedlings on days 2 and 4 then incubated, the endopeptidaseactivity started to decrease just after removal of the axisbut the carboxypeptidase activity increased more markedly thanwhen the axis remained attached. Exogenously supplied GA3, kinetin,IAA, or their combinations, showed no significant effect onthe developmental patterns of the endopeptidase and carboxypeptidaseactivities in cotyledons. These results are discussed in relationto the role of the axis in controlling peptidase formation incotyledons of germinating V. mungo seeds. (Received November 18, 1983; Accepted February 28, 1984)  相似文献   

13.
Diffusion resistance to oxygen within nodules was calculatedusing the respiratory quotient (RQ) of nodules from intact plantsof subterranean clover (Trifolium subterraneum L.) cv. SeatonPark nodulated by Rhizobiun trifolii WU95. From 21 to 52% O2,the RQ remained between 0.94 and 1.04, whereas at 10% O2, theRQ was 1.65. When nodulated roots of intact plants were exposedto sub-ambient pO2 in a continuous flow-through system, respirationdeclined immediately, followed by a partial recovery within30 min. The magnitude of the final respiration rate was dependentupon the pO2 in the gas stream. Initial rates of respirationwere re-established after 24 h at sub-ambient pO2 as a resultof changes in the resistance of the variable barrier to oxygendiffusion within the nodules. Nitrogenase activity also decreasedlinearly with decreasing pO2 in the gas stream, but partialrecovery occurred after 24 h incubation at sub-ambient pO2.Maximum rates of nitrogenase activity occurred at rhizosphereoxygen concentrations between 21% and 36% O2. Resistance tothe diffusion of oxygen within the nodules increased at supra-ambientpO2 and at oxygen concentrations above 36% O2, resulted in adecrease in both nitrogenase activity and nodulated root respiration.The diffusion resistance of nodules to oxygen increased rapidlyin the presence of either supra-ambient pO2 or saturating pC2H2.Reductions in nodule diffusion resistance either during recoveryfrom exposure to 10% acetylene or to sub-ambient pO2 occurredmore slowly. It is concluded that subterranean clover is welladapted for maximum nitrogen fixation at ambient pO2. Key words: Nitrogenase activity, oxygen, subterranean clover, diffusion resistance  相似文献   

14.
Short-term effects of water deficit on nitrogenase activitywere investigated with hydroponically grown soybean plants (Glycinemax L. Merr. cv. Biloxi) by adding polyethylene glycol (PEG)to the hydroponic solution and measuring nitrogenase activity,nodule respiration, and permeability to oxygen diffusion (Po).These experiments showed a rapid decrease in acetylene reductionactivity (ARA) and nodule respiration. A consequence of thedecreased respiration rate was that Po calculated by Fick'sLaw also decreased. However, these results following PEG treatmentwere in direct conflict with a previous report of stabilityin Po determined by using an alternative technique. To resolvethis conflict, an hypothesis describing a sequence of responsesto the initial PEG treatment is presented. An important findingof this study was that the response to water deficit inducedby PEG occurred in two stages. The first stage of decreasednodule activity was O2-limited and could be reversed by exposingthe nodules to elevated pO2. The second stage which developedafter 24 h of exposure to PEG resulted in substantial loss innodule activity and this activity could not be recovered withincreased pO2. Severe water deficit treatments disrupt noduleactivity to such a degree that O2 is no longer the major limitation. Key words: Glycine max, N2 fixation, soybean, oxygen permeability, water deficit  相似文献   

15.
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   

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.
Recent data support the hypothesis that reactive oxygen species (ROS) play a central role in the initiation and progression of vascular diseases. An important vasoprotective function related to the regulation of ROS levels appears to be the antioxidant capacity of nitric oxide (NO). We previously reported that treatment with NO decreases phosphotyrosine levels of adapter protein p130cas by increasing protein tyrosine phosphatase-proline, glutamate, serine, and threonine sequence protein (PTP-PEST) activity, which leads to the suppression of agonist-induced H2O2 elevation and motility in cultured rat aortic smooth muscle cells (SMCs). The present study was performed to investigate the hypotheses that 1) IGF-I increases the activity of the small GTPase Rac1 as well as H2O2 levels and 2) NO suppresses IGF-I-induced H2O2 elevation by decreasing Rac1 activity via increased PTP-PEST activity and dephosphorylation of p130cas. We report that IGF-I induces phosphorylation of p130cas and activation of Rac1 and that NO attenuates these effects. The effects of NO are mimicked by the overexpression of PTP-PEST or dominant-negative (dn)-p130cas and antagonized by the expression of dn-PTP-PEST or p130cas. We conclude that IGF-I induces rat aortic SMC motility by increasing phosphotyrosine levels of p130cas and activating Rac1 and that NO decreases motility by activating PTP-PEST, inducing dephosphorylating p130cas, and decreasing Rac1 activity. Decreased Rac1 activity lowers intracellular H2O2 levels, thus attenuating cell motility. hydrogen peroxide; protein tyrosine phosphatase-proline, glutamate, serine, and threonine sequence protein; p130cas  相似文献   

18.
Alanine aminotransferase increased in pumpkin cotyledons duringgermination with the greatest increase occurring in green cotyledons.The enzyme was found in the soluble fraction and was inhibitedby NH2OH and p-chloromercuribenzoate. Pyridoxal phosphate andglutathione or dithiothreitol overcame die respective inhibition.Dialysis of the enzyme reduced enzyme activity but the activitywas restored by the addition of pyridoxal phosphate. Alanineaminotransferase was proposed to play a major role in the synthesisof the alanine which occurs in pumpkin cotyledons during germination. (Received September 17, 1975; )  相似文献   

19.
Distribution of iron-containing oxidases in aging nodal rootsof rice and wheat was studied. Activities of cytochrome c oxidase(1.9.3.1 [EC] , cytochrome c : O2 oxidoreductase), catalase (1.11.1.6 [EC] ,H2O2: H2O2 oxidoreductase) and peroxidase (1.11.1.7 [EC] , donor:H2O2 oxidoreductase) in wheat roots were comparatively higherthan were those in rice roots at corresponding stages. Cytochromec oxidase in roots remained active throughout the lives of therice and wheat crops. In rice roots, catalase seemed to playa distinct role around the panicle formation stage. Decay ofcatalase activity took place earlier than did that of peroxidaseand cytochrome c oxidase activities. In wheat roots similarenzyme activity changes were not observed. Data may suggestthat the high activity of iron containing oxidases at the panicleformation stage (I) may be chiefly due to catalase activityin rice roots. 1Paper presented at the 14th Annual Meeting of the Society ofthe Science of Soil and Manure, Japan (1968). (Received November 21, 1968; )  相似文献   

20.
The kinetics of the flash induced 518 nm absorbance change (A518)in lettuce leaves were found to be dependent on O2 concentration.(1) Either a lower O2 partial pressure or the addition of weakred background illumination accelerated the decay of (A518)while far-red background light induced a transient acceleration.(2) In the presence of background red light the accelerateddecay could be restored to the original dark level by the additionof O2. A linear relationship was found between the intensityof red background light and the O2 pressure required for thisrestoration. (3) The O2 dependence of (A518) decay halftimewas biphasic, the sensitive phase saturating at 0.3 atmospheresO2 independent of input light energy while the O2 concentrationneeded to saturate the second phase increased with increasinginput light energy (increasing flash frequency). (4) Treatmentwith N, N'-dicyclohexylcarbodiimide (DCCD) or KCN eliminatedall O2 and background light effects and DCMU treatment inhibitedall but the sensitive phase of the O2 dependence on (A518) decayhalftime. (5) The extent of the lag phase in the dark recoveryof (A518) normally present after preillumination induced accelerationof decay was decreased with added O2 or KCN. (6) It was concludedthat O2 competes directly with background red light inducedelectron transport to PS I acceptors to influence the (A518)decay. A possible mechanism involving the O2 sensitive ferredoxin-thioredoxin-reductaseactivation of chloroplast coupling factor 1 ATP-hydrolase activitywas discussed. (Received December 17, 1982; Accepted April 28, 1983)  相似文献   

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