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1.
The formation of singlet molecular oxygen (1O2) in illuminatedchloroplasts and the effects of 1O2 on oxidation or destructionof components and functional integrity of chloroplasts werestudied. The rate of photoreduction of 2,6-dichloroindophenol(DCIP) and the extent of the 515-nm absorbance change were decreasedby light irradiation and by xanthine oxidase treatment. Malondialdehyde(MDA) formation, an indicator of lipid peroxidation, was observedin the light-irradiated chloroplast fragments, but not in thexanthine-xanthine oxidase-treated chloroplast fragments. MDAformation was absent under anaerobic conditions. MDA formation was stimulated when electron transfer on the oxidizingside of photosystem II (or I) was inhibited or inactivated bycarbonylcyanide m-chlorophenylhydrazone (CCCP), Tris-treatment,prolonged illumination, etc. MDA formation was also stimulatedby 3-(3,4-dichlorophenyl)-1, 1-dimethylurea (DCMU) when electrontransfer between water and the reaction center of photosystemII was intact. CCCPor DCMU-stimulated MDA formation was inhibitedby 1,4-diazabicyclo[2.2.2]octane, a quencher of singlet molecularoxygen (1O2). DCMU and electron donors for photosystem II, suchas ascorbate, hydroquinone and semicarbazide, inhibited MDAformation by illumination of the Tris-washed or CCCP-poisonedchloroplast fragments. Reduced DCIP, an electron donor for photosystemI, also inhibited MDA formation in the presence of DCMU. These results lead to the conclusion that MDA formation wasinitiated by 1O2 formed in illuminated chloroplasts. Of thethree mechanisms discussed for 1O2 generation in illuminatedchloroplasts, the formation by the electron transfer reactionbetween superoxide anion radical and the oxidant formed on theoxidizing side of photosystem II (or I) is mostimportant. (Received March 31, 1975; )  相似文献   

2.
The light-induced oxygen evolution, photoreduction of 2,6-dichlorophenolindophenol (DPIP) and carotenoid photobleaching induced by carbonylcyanide m-chlorophenylhydrazone (CCCP) were investigated withspinach chloroplast fragments in the presence of H2O2. Oxygenevolution in the presence of H2O2 was not inhibited by CCCPand was only partially inhibited by 5 µM 3-(3,4-dichlorophenyl)-1,1-dimethylurea(DCMU) which completely inhibited the Hill reaction with DPIP.The degree of inhibition by DCMU was decreased by a simultaneousaddition of CCCP. Carotenoid photobleaching in the presenceof CCCP was stimulated by H2O2. The CCCP-induced carotenoidphotobleaching was completely inhibited by DCMU. However, itwas only partially inhibited by DCMU in the presence of H2O2.These data indicate that H2O2 donates electrons at a site betweenthe CCCP-sensitive site and the reaction center of photosystemII and is reduced at a site between the DCMU-blocked site andthe reaction center of photosystem II. 1Present address: Department of Biology, Kyushu Dental College,Kitakyushu 803, Japan. (Received June 20, 1974; )  相似文献   

3.
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.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% O2 at high light intensity (200 W.m–2),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   

4.
Light filters and metabolic inhibitors have been used to investigatefurther the active transport of sulphate into Chara australis.Two states of influx, light (basal) and dark (transiently stimulated),have been described. The stimulated state noted on transferto dark has been found when the incident intensity of monochromaticlight is reduced, and when photosystem 2 in photosynthesis isinhibited, either by use of cut-ofT filters or by DCMU. Thelight influx is insensitive to CCCP when photosynthetic 14CO2fixation is totally inhibited, and is less sensitive to DNPthan the dark influx. Dark influx is inhibited by CCCP, DNP,and NaCN but is insensitive to DCMU. It is proposed that a respiratoryATP source may be sufficient energy supply for sulphate influxand that the state of influx is under separate control. It issuggested that a ‘triggering’ mechanism may bringabout the change from the light- to the dark-influx state.  相似文献   

5.
Light-induced changes in membrane potential in Spirogyra   总被引:2,自引:0,他引:2  
Spirogyra cells exhibited changes in membrane potential whenthey were exposed to light. Cells made chloroplast-free didnot show any light-induced potential change (LPC) upon illuminationwith white light and also monochromatic red (680 nm) and farred (720 nm) light. LPC was observed when the cell containedonly a small fragment of chloroplast, whether the cell had anucleus or not. The magnitude of LPC depended on the amountof chloroplast in the cell. DCMU at 10–5 M, CCCP at 10–5 M and DNP at 10–4M at pH 5.5 suppressed LPC, while CCCP at 1–5 ? 10–6M, NH4Cl at 5 ? 10–2 M and DNP at 10–4 M at pH 7.0stimulated LPC. PMS at 10–4 M stimulated LPC and couldinduce LPC which was completely inhibited by DCMU. These factssuggest that LPC is related to noncyclic and cyclic electronflows. The influences of light and dark conditions and various metabolicinhibitors (DCMU, DNP, CCCP, NH4Cl) on ATP level have been investigated.No significant difference in the ATP level was observed betweencells in the light and dark. DNP at 10–4 M (pH 5.5) andCCCP at 5 ? 10–6 M decreased the ATP level significantly,while DCMU and NH4Cl only slightly. Good correlation was notfound between the total ATP level and LPC in Spirogyra. LPC occurred even when the external medium contained only asingle salt such as KCl, NaCl or CaSO4. LPC was also recorded in chloroplasts in situ and in vitro.The mode of LPC of chloroplasts was quite different from thatof the cell. On illumination, the chloroplast potential changedvery rapidly and transiently in the positive direction thenrecovered spontaneously to almost the original potential level. Possible causes of LPC are discussed in relation to the electrogenicion pump. 1 Present address: Department of Botany, Faculty of Science,University of Tokyo, Hongo, Bunkyo, Tokyo 113, Japan. (Received November 9, 1977; )  相似文献   

6.
The light-dependent production of hydroxyl radicals (HO{dot})by thylakoids, chloroplasts and leaves of Spinacia oleraceawas investigated using dimethylsulfoxide as HO{dot} trappingagent. Maximum rates of HO{dot} production by thylakoids asindicated by the formation of methane sulfinic acid were observedunder aerobic conditions in the absence of added electron acceptors.They were higher than 2 µmol (mg Chl h)–1. Saturationof HO{dot} production occurred at the low photon flux densityof 100 µmol m–2 s–1. Trapping of HO{dot} bydimethylsulfoxide suppressed, but did not eliminate light-dependentinactivation of PSI and II suggesting that HO{dot} formationcontributed to the photosensitivity of isolated thylakoids.DCMU inhibited HO{dot} formation. Importantly, methylviologendecreased HO{dot} formation in the absence, but stimulated itin the presence of Fe3+. In intact chloroplasts, HO{dot} formation became appreciableonly after KCN had been added to inhibit effective H2O2 scavengingby ascorbate peroxidase. It was stimulated by ferrisulfate,but not by ferricyanide which does not penetrate the chloroplastenvelope. Infiltrated spinach leaves behaved similar in principleto intact chloroplasts in regard to HO{dot} formation but HO{dot}production was very slow if detectable at all by the formationof methylsulfinic acid indicating effective radical detoxification. HO{dot} formation is interpreted to be the result of a Fenton-typereaction which produces HO{dot} in chloroplasts from H2O2 andreduced ferredoxin, when O2 is electron acceptor in the Mehlerreaction and radical detoxification reactions are inhibited. (Received November 13, 1996; Accepted April 23, 1996)  相似文献   

7.
Chlorophyll a and carotenoids of spinach began to be destroyed2 to 3 hr after fumigation with 2 ppm SO2 under light, whereaschlorophyll b was undamaged during 8 hr of exposure to SO2.Pheophytin a was not affected by the fumigation. When disks excised from leaves fumigated with SO2 at 2 ppm for2 hr were illuminated, chlorophyll a and carotenoids were brokendown, while they were not destroyed in darkness. The destructionof these pigments was suppressed under nitrogen. Chlorophylla destruction was inhibited by l,2-dihydroxybenzene-3,5-disulfonate(tiron), hydro-quinone and ascorbate, but not by l,4-diazabicyclo-[2,2,2]-octane(DABCO), methio-nine, histidine, benzoate and formate. Chlorophylla destruction was inhibited by phenazine methosulfate but stimulatedby methyl viologen. Addition of superoxide dismutase (SOD) tothe homogenate of SO2-fumigated leaves inhibited the chlorophylla destruction. The activity of endogenous SOD was reduced to40% by 2-hr fumigation before the loss of chlorophyll was observed.These results suggest that chlorophyll a destruction by SO2was due to superoxide radicals (O2). Moreover, malondialdehyde (MDA), a product of lipid peroxidation,was formed in SO2-fumigated leaves. MDA formation was inhibitedby tiron, hydroquinone and DABCO but not by benzoate and formate.MDA formation was increased by D2O. These results suggest thatlipid peroxidation in SO2-fumigated leaves was due to singletoxygen 1O2 produced from O2. (Received May 15, 1980; )  相似文献   

8.
Chlorophyll a and carotenoids of spinach began to be destroyed2 to 3 hr after fumigation with 2 ppm SO2 under light, whereaschlorophyll b was undamaged during 8 hr of exposure to SO2.Pheophytin a was not affected by the fumigation. When disks excised from leaves fumigated with SO2 at 2 ppm for2 hr were illuminated, chlorophyll a and carotenoids were brokendown, while they were not destroyed in darkness. The destructionof these pigments was suppressed under nitrogen. Chlorophylla destruction was inhibited by l,2-dihydroxybenzene-3,5-disulfonate(tiron), hydro-quinone and ascorbate, but not by l,4-diazabicyclo-[2,2,2]-octane(DABCO), methio-nine, histidine, benzoate and formate. Chlorophylla destruction was inhibited by phenazine methosulfate but stimulatedby methyl viologen. Addition of superoxide dismutase (SOD) tothe homogenate of SO2-fumigated leaves inhibited the chlorophylla destruction. The activity of endogenous SOD was reduced to40% by 2-hr fumigation before the loss of chlorophyll was observed.These results suggest that chlorophyll a destruction by SO2was due to superoxide radicals (O2). Moreover, malondialdehyde (MDA), a product of lipid peroxidation,was formed in SO2-fumigated leaves. MDA formation was inhibitedby tiron, hydroquinone and DABCO but not by benzoate and formate.MDA formation was increased by D2O. These results suggest thatlipid peroxidation in SO2-fumigated leaves was due to singletoxygen 1O2 produced from O2. (Received May 15, 1980; )  相似文献   

9.
Chemiluminescence of luminol (CLL) was induced by illuminatedspinach chloroplast fragments. CLL was diminished by superoxidedismutase or under anaerobic conditions and increased by anautoxidizable electron acceptor, methyl viologen. The optimumpH for CLL was 10.0-10.5. Ferredoxin and cytochrome c reducing substance (CRS) did notaffect the intensity of CLL, but accelerated the dark decayin the absence of methyl viologen. In the presence of methylviologen, ferredoxin and CRS lowered the intensity and acceleratedthe dark decay. 3-(4-Chlorophenyl)-1,1-dimethylurea diminishedCLL. Carbonylcyanide m-chlorophenylhydrazone accelerated theinitial rate of CLL increase at low concentration and inhibitedit at high concentration. Half-decay time of CLL after the cessationof light was shortened by inhibiting electron transfer on theoxidizing side of photosystem II. We conclude that most of the CLL observed in illuminated chloroplastsis dependent on O2. The results also suggest that O2is reduced by reduced ferredoxin or CRS and oxidized on theoxidizing side of photosystem II. The half life of O2in illuminated chloroplasts was estimated from the half-decaytime of CLL to be a few sec. 1 Present address: Kyushu Dental College, Department of Biology,Kitakyushu 803, Japan. (Received May 30, 1977; )  相似文献   

10.
The aim of the present study is to detect the monodehydroascorbicacid (MDA) radical in broad bean (Vicia faba L.) leaves whichwere treated by vacuum-infiltration in Na2SO3 solution and subsequentcentrifugation (sulfite-treated leaves). When sulfite-treatedleaves were illuminated with white light, the electron spinresonance (ESR) signal of MDA radical was observed. The levelof the MDA radical depended on the concentration of sulfitethat was used for vacuum-infiltration and on the light intensityof illumination. The formation of the MDA radical in sulfite-treatedleaves was inhibited by DCMU or by replacement of air with N2.Glycolaldehyde also inhibited the formation of MDA radical insulfite-treated leaves. Catalase activity was decreased by thesulfite treatment without affecting significantly the activitiesof ascorbate peroxidase (AA-POX) and of peroxidase which preferentiallyoxidizes phenolics (PhOH-POX). From these results, we concludethat the formation of the MDA radical in sulfite-treated leavesis catalyzed by peroxidases using the H2O2 which is generatedby photorespiration and the Mehler reaction. 1On leave from the Center for Multidisciplinary Studies, Universityof Belgrade, Yugoslavia.  相似文献   

11.
Photosynthetic Properties of Guard Cell Protoplasts from Vicia faba L.   总被引:3,自引:0,他引:3  
Guard cell protoplasts were isolated enzymatically from theepidermis of Vicia faba L. and their photosynthetic activitieswere investigated. Time courses of light-induced changes inthe chlorophyll a fluorescence intensity of these protoplastsshowed essentially the same induction kinetics as found formesophyll protoplasts of Vicia. The transient change in thefluorescence intensity was affected by DCMU, an inhibitor ofphotosystem II; by phenylmercuric acetate, an inhibitor of ferredoxinand ferredoxin NADP reductase; and by methyl viologen, an acceptorof photosystem I. Low temperature (77 K) emission spectra ofthe protoplasts had peaks at 684 and 735 nm and a shoulder near695 nm. A high O2 uptake (175 µmol mg–1 Chl hr–1)was observed in guard cell protoplasts kept in darkness, whichwas inhibited by 2 mM KCN or NaN3 by about 60%. On illumination,this O2 uptake was partially or completely suppressed, but itssuppression was removed by DCMU, which indicates that oxygenwas evolved (150 µmol mg–1 Chl hr–1) photosynthetically.We concluded that both photosystems I and II function in guardcell chloroplasts and that these protoplasts have high respiratoryactivity. (Received January 30, 1982; Accepted May 15, 1982)  相似文献   

12.
The luciferin-luciferase method was used to determine ATP extractedfrom darkmaintained and light-exposed samples of the green algaChlorella pyrenoidosa and of the blue-green alga Anacystis nidulans.A few measurements on Synechococcus lividus (a bluegreen thermophile,clone 65?C) are also reported.
  1. The light-minus-dark ATP levels (ATP) from aerobic cells ofChlorella and Anacystis were negative; however, ATP from Synechococcuswas positive. Large positive ATP was obtained in regularly grown(RG: moderate light) Chlorella treated with oligomycin; darklevels were reduced, light levels remained essentially unaffected.In high-light exposed (HLE) Chlorella, oligomycin reduced bothlight and dark ATP levels, but positive ATP was still obtained.However, in Anacystis, which has a different organization ofthylakoid membrane, oligomycin severely reduced both the lightand the dark ATP levels and the ATP remained negative.
  2. Theoligomycin (12 µM) treated Chlorella and the untreatedAnacystis and Synechococcus show the presence of cyclic photophosphorylationunder conditions in which the non-cyclic electron flow fromphotosystem II to photosystem I is blocked by 10 µM 3-(3,4-dichlorophenyl)-l,l-dimethylurea(DCMU), or not allowed to operate by the absence of CO2. Cyclicphotophosphorylation ranged from 10–30% of the maximumATP in RG, to 40–50% in HLE Chlorella. In RG Chlorella,cyclic and non-cyclic (in the absence of DCMU) photophosphorylation(ATP) saturate at about 103 ergs cm–2 sec–1 and104 ergs cm–2 sec–1 and 104 ergs cm–2 sec–1red (>640 nm) light, respectively; a lag was observed inthe light curve.
  3. In Chlorella, the addition of the photosystemI electron acceptormethyl viologen (MV; 1 mM) increased ATPby twofold. Furtheraddition of DCMU (25 µm) reduced thisto the level observedwith DCMU alone. If 1 mM reduced dichlorophenolindophenol orphenazine methosulphate (DCPIPH2 or PMSH2, respectively)wasadded along with DCMU, the ATP level was 30–40% ofthecontrol. Further addition of MV increased the JATP to be70–80%of that of the control. These and other resultsconfirm thepresence of both non-cyclic and cyclic photophosphorylationin vivo, the former predominating in Chlorella, and the latterin Anacystis and Synechococcus.
(Received May 1, 1973; )  相似文献   

13.
The effects of deuterium oxide (D2O) on light-induced lipidperoxidation and carbonylcyanide m-chlorophenylhydrazone (CCCP)-inducedcarotenoid photobleaching were examined in isolated chloroplastfragments. D2O stimulated the lipid peroxidation in the presenceof CCCP or methyl viologen as well as in their absence. Carotenoidphotobleaching was also enhanced by D2O. These results led tothe conclusion that the lipid peroxidation and part of the carotenoidphotobleaching were induced by the singlet molecular oxygenbecause D2O prolongs its lifetime. (Received June 23, 1978; )  相似文献   

14.
Normal Euglena chloroplasts contained 1 atom of Mn per 47±8chlorophyll molecules. The manganese content of chloroplastswas decreased by heat treatment. After complete removal of manganeseby incubation at 45°C for 5 min, Hill activity with DPIPas electron acceptor was abolished, but the activity of DPIPphotoreduction with diphenylcarbazide as electron donor wasunaffected. Hill activity was inactivated by incubating Euglena chloroplastsat alkaline pH. The presence of a high concentration of Trisduring incubation of chloroplasts at an alkaline pH had no additionaleffect on the activity drop. Donor-supported DPIP photoreduction in heated Euglena chloroplasts,as well as the normal Hill reaction in untreated chloroplasts,was inhibited by DCMU, HOQNO and ioxynil which block electrontransport at the reducing side of system II. These reactionswere also inhibited by another group of inhibitors; CCCP, salicylaldoxime,antimycin A and azide, which block electron transport at a sitebetween the electron carriers, Y1 and Y2 located on the oxidizingside of system II. Possible sites of inhibition by heat treatment and by inhibitorsand sites for entry of electrons from artificial electron donorsin the photosynthetic electron transport chain, especially inrelation to the functional site of endogenous manganese in chloroplasts,were proposed. (Received October 30, 1971; )  相似文献   

15.
The generally observed light-induced uptake of protons intothe thylakoid lumen is diminished by adding protonophores. Insteadof the H+ uptake, the release of protons was observed duringillumination in the presence of various protonophores at highconcentrations, namely, 1 µM nigericin, 10 µM carbonylcyanidem-chlorophenylhydrazone or 30 µM gramicidin. An uncoupler,NH4C1 (4 mM), and a detergent, Triton X-100 (0.02%), also inducedthe H+ release but a K+ ionophore, valinomycin, did not. Theamount of H+ released reached about 100 nmol H+ (mg Chl)–1at pH 7.5 under continuous illumination. The rate of the H+release was similar to that of the conventional H+ uptake butits dark relaxation was much slower than that of the H+ uptake.We compared the H+ release in protonophore-added thylakoidswith the previously reported H+ release in coupling factor 1(CF1-depleted thylakoids. The H+ release in thylakoids withnigericin showed similar characteristics to that in CF1-depletedthylakoids in terms of their responses to pH, phenazine methosulfateand light intensity. Both types of H+ release were relativelyinsensitive to DCMU and were stimulated somewhat by DCMU atlow concentrations (around 200 nM). Nigericin did not inhibitthe superoxide dismutase activity of the membranes. These resultsindicate that the H+ release in protonophore-added thylakoidsand that in CF1 depleted thylakoids involve the same mechanismand that water-derived protons from PS II that result from animpairment of the activity of superoxide dismutase, as previouslyproposed, are not involved. Judging from the rate of electronflow and the lumenal acidification under the illumination, weconclude that the H+ release is a light-dependent scalar processwhich can be observed in thylakoid membranes with high H+ permeability.The H+ release of this type was not observed in mitochondriafrom rat liver or in chromatophores from Rhodobacter sphaeroides. (Received November 29, 1990; Accepted June 27, 1991)  相似文献   

16.
Light-induced redox-reactions of cytochrome b559 in spinachchloroplasts were investigated. Illumination of chloroplastsinduced photoreduction of cytochrorne b559 Red light (650 nm)was more effective than far-red light (725 nm), indicating thatthe photoreduction is a photosystem II-mediated reaction. Onaddition of DCMU, the photoreduction was eliminated and a photooxidationof cytochrome b559 was observed. The rate of this photooxidationwas faster with photosystem II light than with photo-systemI light. On addition of Mn++ the photooxidation was partly suppressed;far-red light became as effective as red light in inducing photooxidationof cytochrome b599, in the presence of DCMU and Mn++. Ascorbate completely suppressed photooxidation of cytochromeb559 In the presence of ascorbate, however, photooxidation wasobserved in the presence of inhibitors or after inhibitory treatmentsof chloroplasts which affected the oxidizing side of systemII. These inhibitors and inhibitory treatments, but not DCMU,decreased the redoxpotential of cytochrome b559. Reactivationof Hill reaction in Tris-washed chloroplasts by indophenol-ascorbatetreatment was not accompanied by an abolishment of photooxidationof cytochrome b559. A possible mechanism is proposed to account for these reactionsof cytochrome b559 in the photosynthetic electron transportin chloroplasts. (Received April 4, 1972; )  相似文献   

17.
Perfused Chara cells were used to measure the rapid light-inducedpotential change (rapid LPC) caused by activation of a K+ channelin the plasma membrane through photosynthesis in the presenceof various photosynthetic inhibitors. The rapid LPC was inhibitedby DCMU but recovered on addition of phenazinemethosulfate (PMS)in the presence of DCMU. Carbonylcyanide m-chlorophenylhydrazone(CCCP) stimulated the rapid LPC. DCCD partially inhibited therapid LPC with a partial inhibition of oxygen evolution. Itis concluded that both cyclic and noncyclic electron flows arecoupled with the rapid LPC. To understand the mechanism of K+ channel activation by photosyntheticelectron flow, the rapid LPC was measured under continuous internalperfusion. It was suggested that a diffusible substance wasnot released from chloroplasts, since vigorous continuous perfusiondid not inhibit the rapid LPC. The suggestion that the rapid LPC is caused by changes in surfacecharge density of chloroplasts was supported by the fact thatthe rapid LPC was inhibited by increasing the ionic strengthof the perfusion medium. (Received February 28, 1986; Accepted April 30, 1986)  相似文献   

18.
The effect of the intracellular concentration of ATP ([ATP]1)on the light-induced potential change (LPC) in tonoplast-freeChara cells was studied. The LPC was hardly affected by loweringthe [ATP]1 by about 1/10 or by raising it to about 10 timesthe normal cytoplasmic concentration (0.5–1.3 mM). Theinsensitivity of LPC to [ATP]1 excludes the possibility thatan increase in [ATP]1 due to photosynthesis may induce the LPC.However, extreme lowering of the [ATP]1 to about 1–2 µMcompletely inhibited LPC, although photosynthetic O2 evolutionwas not significantly inhibited. This fact supports the hypothesisthat light stimulates the putative H+pump fueled by ATP. Theuncoupling agents DNP and CCCP greatly depolarized the membrane,and inhibited LPC strongly, but they did not decrease [ATP]1.Photosynthetic O2 evolution was inhibited to some extent by2 µM CCCP and strongly inhibited by 0.1 mM DNP. Sincethe membrane resistance increased significantly, these chemicalsare believed to act on the membrane as an inhibitor of the electrogenicH+ pump not as an H+conductor. Introduction of 1 mM ATP intocells treated with uncouplers, to a large extent restored theirability to produce LPC although the membrane potential in darknesswas maintained at a low level. 1Present address: Niigata College of Pharmacy, 5829 Kamishinei-cho,Niigata 950-21, Japan. 2Present address: Department of Agricultural Chemistry, Collegeof Agriculture, Kyoto University, Kyoto 606, Japan. 3Present address: Department of Botany, Faculty of Science,University of Tokyo, Hongo, Tokyo 113, Japan. (Received March 9, 1979; )  相似文献   

19.
Redox Reactions between Kaempferol and Illuminated Chloroplasts   总被引:5,自引:2,他引:3       下载免费PDF全文
Bleaching of kaempferol by illuminated chloroplasts was observed at 380 nanometers. The photobleaching was stimulated by methyl viologen and suppressed by superoxide dismutase indicating the participation of O2 in the reaction. An electron transfer inhibitor on the oxidizing side of photosystem II, carbonylcyanide m-chlorophenylhydrazone (CCCP), stimulated the photobleaching and 3-(3,4-dichlorophenyl)-1,1-dimethylurea partially suppressed it. The stimulation by CCCP suggests that kaempferol is also bleached on the oxidizing side of photosystem II. The spectrum of kaempferol bleaching in the presence of methyl viologen was the same as that in the presence of CCCP having a maximum in absorbance decrease at around 380 nanometers. When kaempferol was oxidized by KMnO2 or KO2, the oxidized minus reduced difference spectra had also a negative peak at about 380 nanometers. The results suggest that kaempferol was oxidized by illuminated chloroplasts.

The rate of kaempferol photooxidation increased as its concentration was increased from 1 to 100 micromolar. The rate of quercetin photooxidation also increased as its concentration was increased from 1 to 100 micromolar. Concentration of quercetin glycosides higher than 10 micromolar was required to detect their photobleaching by illuminated chloroplasts. From these results, it is postulated that flavonols function as antioxidants in chloroplasts.

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20.
The effects of cyanide on the electron flow in NO3 andNO2 reductions and photosynthetic electron transfer wereinvestigated with intact cells of a photodenitrifier, Rhodobactersphaeroides f. s. denitrificans. In the presence of 30 µMKCN, electron transfer for NO3 reduction was inhibitedby about 70% and the concomitant H translocation was completelyinhibited. However, neither NO2 reduction nor photosyntheticcyclic electron transfer was affected at 30 µM. Theseresults suggested that the electron transfer pathway to NO3has, in addition to a b-type cytochrome and the nitratereductase,a component sensitive to a low concenration of cyanide whichis not involvedin the cytochrome bc1 complex. (Received April 13, 1987; Accepted July 23, 1987)  相似文献   

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