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1.
1. The ATP analog, adenylyl-imidodiphosphate rapidly inhibited CO2-dependent oxygen evolution by isolated pea chloroplasts. Both α, β- and β, γ-methylene adenosine triphosphate also inhibited oxygen evolution. The inhibition was relieved by ATP but only partially relieved by 3-phosphoglycerate. Oxygen evolution with 3-phosphoglycerate as substrate was inhibited by adenylyl-imidodiphosphate to a lesser extent than CO2-dependent oxygen evolution. The concentration of adenylyl-imidodiphosphate required for 50% inhibition of CO2-dependent oxygen evolution was 50 μM.2. Although non-cyclic photophosphorylation by broken chloroplasts was not significantly affected by adenylyl-imidodiphosphate, electron transport in the absence of ADP was inhibited by adenylyl-imidodiphosphate to the same extent as by ATP, suggesting binding of the ATP analog to the coupling factor of phosphorylation.3. The endogenous adenine nucleotides of a chloroplast suspension were labelled by incubation with [14C]ATP and subsequent washing. Addition of adenylyl-imidodiphosphate to the labelled chloroplasts resulted in a rapid efflux of adenine nucleotides suggesting that the ATP analog was transported into the chloroplasts via the adenine nucleotide translocator.4. It was concluded that uptake of ATP analogs in exchange for endogenous adenine nucleotides decreased the internal ATP concentration and thus inhibited CO2 fixation. Oxygen evolution was inhibited to a lesser extent in spinach chloroplasts which apparently have lower rates of adenine nucleotide transport than pea chloroplasts. 相似文献
2.
Cold-acclimation (CA) of the halotolerant alga Dunaliella was inhibited by light and by high salt. CA was associated with enhanced resistance to freezing in saline growth solutions, as manifested by protection of photosynthetic oxygen evolution and by reduced permeabilisation of the plasma membrane. Oxygen evolution activity in isolated chloroplasts was not affected by freezing, but was inhibited by high salt and the inhibition could be reversed or protected by glycerol. The activity of chloroplasts from cold-acclimated cells was more resistant to salt than of non-acclimated cells. Electron transport measurements in chloroplasts indicated that high salt inhibited PS-II, but not PS-I electron transport. High salt also inhibited PS-II thermoluminescence (TL) activity in chloroplasts. Similar inhibition of PS-II TL was observed by freezing intact cells in saline solutions. Chloroplasts from cold-acclimated cells had enhanced resistance to inhibition of PS-II electron transport and of PS-II TL by high salt. These results suggest that inhibition of oxygen evolution upon freezing Dunaliella cells may result from inactivation of PS-II due to massive influx of salt and loss of glycerol. The enhanced freeze-resistance of cold-acclimated cells to inhibition of oxygen evolution can be accounted for partly by protection of PS-II against high salt. 相似文献
3.
HANS EGNÉUS 《Physiologia plantarum》1975,33(3):203-213
The oxygen exchange, obtained when isolated chloroplasts of Triticum aestivum, wheat, are irradiated without the addition of a Hill oxidant has been investigated using an oxygen electrode. Ascorbate, catalase, 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone(DBMIB), diethyldithio-carbamate (DEDT), dichlorophenylmethylurea (DCMU), and potassium cyanide were added to the Chloroplasts in order to investigate the oxygen exchange. At least two oxygen uptake reactions, one sensitive to catalase and one catalase-insensitive, appeared upon irradiation. Hydrogen peroxide was the product of the oxygen uptake in the former process, and water was the reductant. The formation of hydrogen peroxide was probably associated with photosystem I. The other oxygen consuming reaction was found to be insensitive to both catalase and potassium cyanide. After the chloroplasts had been treated with DCMU, it was possible to show that the catalase-insensitive oxygen uptake was localized in photosystem I, and that a cyclic electron transport system or some endogenous reductant (-s) acted in the oxygen uptake. Addition of ascorbate or DEDT to the chloroplasts led to an enhanced oxygen uptake in 710 nm light. This was probably due to the effect of these compounds on the superoxide radical ion formed in photosystem I. The stimulated oxygen uptake was only weakly affected by catalase, indicating that hydrogen peroxide was not a product of this oxygen uptake. Addition of DEDT and potassium cyanide inhibited (strongly respectively weakly) the oxygen uptake when photosystem II was functioning. The effect of these compounds was probably due to an inhibition of the electron transport at the plastocyanin. DBMIB inhibited the oxygen uptake reactions and the cooperation between the two photosystems. The cooperation between the photosystems was also studied in DCMU-treated chloroplasts. The reactions in photosystem II, measured as oxygen evolution, were more inhibited than the coupling between the photosystems. The oxygen “gush” appearing upon irradiation in light of 650 nm was not affected by a DBMIB-treatment, showing that the oxygen evolution was due to the reduction of plastoquinone. The reoxidation in the dark of the plastoquinone pool was stimulated by DBMIB and potassium cyanide indicating that an oxygen uptake could be associated with plastoquinone. The sites of interaction of oxygen with the electron transport pathways in chloroplasts, and the different reductants for the oxygen consuming reactions are discussed. 相似文献
4.
A group of 12 alkaloids were tested as inhibitors of photophosphorylation in spinach chloroplasts. Ajmaline, a dihydroindole alkaloid, was found to be the strongest inhibitor of both cyclic and non-cyclic photophosphorylation. Low concentrations of ajmaline also inhibited the dark and light ATPases, and the coupled electron flow from water to ferricyanide, measured either as ferrocyanide formed or as oxygen evolved, but not the uncoupled electron transport or the pH rise of illuminated unbuffered suspensions of chloroplasts. Higher concentrations of ajmaline stimulated, instead of inhibiting, photosynthetic electron transport or oxygen evolution and decreased the pH rise, thus behaving as an uncoupler, such as ammonia.Photophosphorylation was partially inhibited by 100 μM dihydrosanguinarine, 100 μM dihydrochelerythrine (benzophenanthridine alkaloids); 500 μM O,O'-dimethylmagnoflorine, 500 μM N-methylcorydine (aporphine alkaloids) and 1 mM julocrotine. They also inhibited coupled oxygen evolution and only partially (dihydrosanguinarine and dihydrochelerythrine) or not at all (the other alkaloids) uncoupled oxygen evolution.Spegazzinine (dihydroindole alkaloid), magnoflorine, N-methylisocorydine, coryneine (aporphine alkaloids), candicine and ribalinium chloride were without effect on photophosphorylation at 500 μM. 相似文献
5.
Oxygen ist reduced by the electron transport chain of chloroplasts during CO2 reduction. The rate of electron flow to oxygen is low. Since antimycin A inhibited CO2-dependent oxygen evolution, it is concluded that cyclic photophosphorylation contributes ATP to photosynthesis in chloroplasts which cannot satisfy the ATP requirement of CO2 reduction by electron flow to NADP and to oxygen. Inhibition of photosynthesis by antimycin A was more significant at high than at low light intensities suggesting that cyclic photophosphorylation contributes to photosynthesis particularly at high intensities. Cyclic electron flow in intact chloroplasts is under the control of electron acceptors. At low light intensities or under far-red illumination it is decreased by substrates which accept electrons from photosystem I such as oxaloacetate, nitrite or oxygen. Obviously, the cyclic electron transport pathway is sensitive to electron drainage. In the absence of electron acceptors, cyclic electron flow is supported by far-red illumination and inhibited by red light. The inhibition by light exciting photosystem II demonstrated that the cyclic electron transport pathway is accessible to electrons from photosystem II. Inhibition can be relieved by oxygen which appears to prevent over-reduction of electron carriers of the cyclic pathway and thus has an important regulatory function. The data show that cyclic electron transport is under delicate redox control. Inhibition is caused both by excessive oxidation and by over-reduction of electron carriers of the pathway. 相似文献
6.
1. A23187 will uncouple electron transport by broken chloroplasts in a divalent cation dependent manner provided that they have been treated with a low concentration of EDTA.2. A23187 stimulates oxaloacetate-dependent oxygen evolution and inhibits phosphoglycerate reduction by intact chloroplasts isolated in a cation-free medium whereas the full effect of nigericin was dependent on the presence of external K+.3. Uncoupling of oxaloacetate reduction by A23187 in intact chloroplasts is inhibited by EDTA and this effect is overcome by excess Mg2+.4. The results suggest that divalent and not monovalent cations are available for collapsing the light-induced H+ gradient within the intact organelle. 相似文献
7.
Rates of vectorial proton transport supported by cyclic electron flow during oxygen reduction by illuminated intact chloroplasts 总被引:3,自引:0,他引:3
The light-dependent quenching of 9-aminoacridine fluorescence was used to monitor the state of the transthylakoid proton gradient in illuminated intact chloroplasts in the presence or absence of external electron acceptors. The absence of appreciable light-dependent fluorescence quenching under anaerobic conditions indicated inhibition of coupled electron transport in the absence of external electron acceptors. Oxygen relieved this inhibition. However, when DCMU inhibited excessive reduction of the plastoquinone pool in the absence of oxygen, coupled cyclic electron transport supported the formation of a transthylakoid proton gradient even under anaerobiosis. This proton gradient collapsed in the presence of oxygen. Under aerobic conditions, and when KCN inhibited ribulose bisphosphate carboxylase and ascorbate peroxidase, fluorescence quenching indicated the formation of a transthylakoid proton gradient which was larger with oxygen in the Mehler reaction as electron acceptor than with methylviologen at similar rates of linear electron transport. Apparently, cyclic electron transport occured simultaneously with linear electron transport, when oxygen was available as electron acceptor, but not when methylviologen accepted electrons from Photosystem I. The ratio of cyclic to linear electron transport could be increased by low concentrations of DCMU. This shows that even under aerobic conditions cyclic electron transport is limited in isolated intact chloroplasts by excessive reduction of electron carriers. In fact, P700 in the reaction center of Photosystem I remained reduced in illuminated isolated chloroplasts under conditions which resulted in extensive oxidation of P700 in leaves. This shows that regulation of Photosystem II activity is less effective in isolated chloroplasts than in leaves. Assuming that a Q-cycle supports a H+/e ratio of 3 during slow linear electron transport, vectorial proton transport coupled to Photosystem I-dependent cyclic electron flow could be calculated. The highest calculated rate of Photosystem I-dependent proton transport, which was not yet light-saturated, was 330 mol protons (mg chlorophyll h)–1 in intact chloroplasts. If H+/e is not three but two proton transfer is not 330 but 220 mol (mg Chl H)–1. Differences in the regulation of cyclic electron transport in isolated chloroplasts and in leaves are discussed. 相似文献
8.
Lei Z Mingyu S Chao L Liang C Hao H Xiao W Xiaoqing L Fan Y Fengqing G Fashui H 《Biological trace element research》2007,119(1):68-76
With a photocatalyzed characteristic, nanoanatase TiO2 under light could cause an oxidation–reduction reaction. Our studies had proved that nano-TiO2 could promote photosynthesis and greatly improve spinach growth. However, the mechanism of nano-TiO2 on promoting conversion from light energy to electron energy and from electron energy to active chemistry energy remains
largely unclear. In this study, we report that the electron transfer, oxygen evolution, and photophosphorylation of chloroplast
(Chl) from nanoanatase-TiO2-treated spinach were greatly increased under visible light and ultraviolet light illumination. It was demonstrated that nanoanatase
TiO2 could greatly improve whole chain electron transport, photoreduction activity of photosystem II, O2-evolving and photophosphorylation activity of spinach Chl not only under visible light, but also energy-enriched electron
from nanoanatase TiO2, which entered Chl under ultraviolet light and was transferred in photosynthetic electron transport chain and made NADP+ be reduced into NADPH, and coupled to photophosphorylation and made electron energy be transformed to ATP. Moreover, nanoanatase
h+, which photogenerated electron holes, captured an electron from water, which accelerated water photolysis and O2 evolution. 相似文献
9.
Effects of lanthanum and calcium on photoelectron transport activity and the related protein complexes in chloroplast of cucumber leaves 总被引:1,自引:0,他引:1
The effects of lanthanum and calcium ions on electron transport, dichlorephenol indophenol (DCIP) photoreduction, and oxygen
evolution activities in chloroplast from cucumber (Cucumis satives L.) were determined. The lanthanum inhibited the whole electron chain-transport activity of chloroplast. DCIP photoreduction
and oxygen evolution activities of the photosystem I (PSII) also decrease after treatment with La3+. But the diminished activities of PSII and chloroplast caused by La3+ could be reversed by Ca2+ and even became higher than the control level. The concentration analysis of related protein complexes to photoelectron transport
in chloroplast included that La3+ induced the concentration of chlorophyll protein complexes increasing but caused some nonchlorophyll protein complexes to
decompose partially. This increasing effect of La3+ on chlorophyll protein complexes results in the improvement of chlorophyll content, which will improve the absorption of
photoelectron and energy transport in the process of photosynthesis. 相似文献
10.
Purified mesophyll protoplasts from the C4 plant Digitaria sanguinalis were used to prepare intact mesophyll chloroplasts with low cytoplasmic contamination. The procedure involved breakage of protoplasts, differential centrifugation, partition in a dextran-polyethylene glycol two-phase system, and Percoll density gradient centrifugation. The final chloroplast preparation contained about 80% intact chloroplasts with a phosphoenolpyruvate carboxylase contamination of 0.2–1% of the original protoplast activity, corresponding to 1–6 μmol 14CO2 fixed/mg Chl h. The purified chloroplasts showed substrate-dependent oxygen evolution in the range of 40–150 μmol substrate reduced/mg Chl h, with phosphoglycerate or oxaloacetate as substrate. Both reactions were stimulated 1.5 fold by pyruvate and further by addition of the other substrate. These measurements indicated that phosphoglycerate reduction was limited by substrate transport across the chloroplast envelope. Without added substrate, the chloroplasts consumed oxygen via pseudo-cyclic electron transport in the light. Also this reaction was stimulated by pyruvate. Phosphoglycerate-dependent oxygen evolution was inhibited by Pi and by phosphoenolpyruvate to about the same extent with purified chloroplasts, but only by Pi with protoplast extracts. This suggests that phosphoglycerate, Pi and phosphoenolpyruvate share a common carrier, similar to the Pi-translocator in C3 chloroplasts, and that the lack of inhibition obtained with phosphoenolpyruvate and unpurified chloroplasts is artefactual, possibly due to oxaloacetate formation from added phosphoenolpyruvate and concomitant stimulation of oxygen evolution by oxaloacetate reduction. Furthermore, the results suggest that phosphoenolpyruvate is transported with a Km similar to that of Pi in C4 mesophyll chloroplasts. 相似文献
11.
A growth regulator (G; 4-ethyl-1-hydroxy-4,8,8,10,10 pentamethyl-7,9-dioxo-2,3 dioxyabicyclo (4.4.0) decene-5) from Eucalyptus grandis (Maiden) reduced stomatal conductance and also photosynthetic capacity when fed through the transpiration stream of detached leaves. The concentration of G required for this effect was high (10−4 molar), but the amount of G taken up (dose) was below the level which has previously been found in E. grandis leaves. Similar effects were observed in detached leaves of Xanthium strumarium L. though almost 10 times more G was required. G reduced CO2-dependent O2 evolution from isolated cells of X. strumarium. In spinach (Spinacia oleracea L.) chloroplasts, electron transport through photosystem II was reduced by G. It is proposed that G affects stomatal conductance and photosynthesis by reducing photosystem II activity in both the guard cell chloroplasts and mesophyll cell chloroplasts. 相似文献
12.
Xiaolan Gong Ying Wang Chao Liu Sisi Wang Xiaoyang Zhao Min Zhou Na Li Yun Lu Fashui Hong 《Biological trace element research》2010,136(3):372-382
The effects of Mn2+ deficiency on light absorption, transmission, and oxygen evolution of maize chloroplasts were investigated by spectral methods.
Several effects of Mn2+ deficiency were observed: (1) the skeleton of pigment protein complexes and oxygen-evolving center and the combination between
pigment and protein were damaged; (2) the light absorption of chloroplasts was obviously decreased; (3) the energy transfer
among amino acids within PS II protein–pigment complex and decreased energy transport from tyrosine residue to chlorophyll
a and from chlorophyll b and carotenoid to chlorophyll a were inhibited; (4) the oxygen-evolving of chloroplast was significantly
inhibited. However, Mn2+ addition decreased the damage of light absorption, transmission, and oxygen evolution of maize chloroplasts caused by Mn2+ deficiency. 相似文献
13.
Abstract A simple mechanical method for the rapid isolation of chloroplasts with high rates of photosynthesis from young leaves of oat (Avena sativa L.) was described. The photosynthetic activity of these chloroplasts was stable for at least 2 h with rates of CO2-dependent O2 evolution of 30–40 μmol g 1 Chl s 1. The photosynthetic properties of these chloroplasts were similar to those reported for spinach and pea chloroplasts isolated by mechanical disruption. The pH optimum for photosynthetic O2 evolution was pH 7.6. The induction time was 0.5–2 min. Maximal rates of photosynthetic O2 evolution in these chloroplast preparations were obtained in the absence of both divalent cations and EDTA. Addition of divilent cations strongly inhibited photosynthesis which could be partially restored by the subsequent addition of EDTA. But when these cations were not present in the assay medium the addition of EDTA greater than 1 mol m 3 decreased photosynthetic activity. The optimal orthophosphate concentration required for photosynthesis in these chloroplast preparations was 0.2–0.3 mol m 3. In contrast, the addition of pyrophosphate either in the light or dark inhibited photosynthesis. In a comparative study, chloroplasts were also isolated from oat and wheat (Triticum aestivum L., cultivar Hybrid C306) protoplasts. These chloroplast preparations were found to have properties similar to those determined for oat chloroplasts isolated by the mechanical method reported above. 相似文献
14.
1. The ATP analog, adenylyl-imidodiphosphate rapidly inhibited CO2-dependent oxygen evolution by isolated pea chloroplasts. Both alpha, beta- and beta, gamma-methylene adenosine triphosphate also inhibited oxygen evolution. The inhibition was relieved by ATP but only partially relieved by 3-phosphoglycerate. Oxygen evolution with 3-phosphoglycerate as substrate was inhibited by adenylyl-imidodiphosphate to a lesser extent than CO2-dependent oxygen evolution. The concentration of adenylylimidodiphosphate required for 50% inhibition of CO2-dependent oxygen evolution was 50 micronM. 2. Although non-cyclic photophosphorylation by broken chloroplasts was not significantly affected by adenylyl-imidodiphosphate, electron transport in the absence of ADP was inhibited by adenylyl-imidodiphosphate to the same extent as by ATP, suggesting binding of the ATP analog to the coupling factor of phosphorylation. 3. The endogenous adenine nucleotides of a chloroplast suspension were labelled by incubation with [14C]ATP and subsequent washing. Addition of adenylyl-imidodiphosphate to the labelled chloroplasts resulted in a rapid efflux of adenine nucleotides suggesting that the ATP analog was transported into the chloroplasts via the adenine nucleotide translocator. 4. It was concluded that uptake of ATP analogs in exchange for endogenous adenine nucleotides decreased the internal ATP concentration and thus inhibited CO2 fixation. Oxygen evolution was inhibited to a lesser extent in spinach chloroplasts which apparently have lower rates of adenine nucleotide transport than pea chloroplasts. 相似文献
15.
Zinc-inhibited Electron Transport of Photosynthesis in Isolated Barley Chloroplasts 总被引:13,自引:1,他引:12
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In isolated barley chloroplasts, the presence of 2 millimolar ZnSO4 inhibits the electron transport activity of photosystem II, as measured by photoreduction of dichlorophenolindophenol, O2 evolution, and chlorophyll a fluorescence. The inhibition of photosystem II activity can be restored by the addition of the electron donor hydroxylamine or diphenylcarbazide, but not by benzidine and MnCl2. These observations suggest that Zn inhibits electron flow at the oxidizing side of photosystem II at a site prior to the electron donating site(s) of hydroxylamine and diphenylcarbazide. No inhibition of photosystem I-dependent electron transport by 3 millimolar ZnSO4 is observed. However, with concentrations of ZnSO4 above 5 millimolar, photosystem I activity is partially inactivated. Washing Zn2+-treated chloroplasts partially restores the O2-evolving activity. 相似文献
16.
Oxygen reduction by isolated chloroplast lamellae from spinach, yielding the superoxide free radical in the light, is stimulated by a fluorescent factor (“compound No. 4”, isolated from Euglena gracilis strain Z) in a ferredoxin-dependent reaction. This reaction is not observed with Euglena chloroplasts, although there is a stimulation by compound No. 4 of ferredoxin-dependent oxygen reduction at the expense of NADPH + H+ as electron donor in the dark. Evidence is provided that in Euglena chloroplasts in the absence of NADP as electron acceptor a cyclic electron transport is predominating, including photosystem I, ferredoxin, NADP-ferredoxin reductase, and cytochrome552. Isolated spinach chloroplast lamellae show a similar “cyclic” electron transport after treatment with digitonin, depending on the addition of the above cofactors. This result might indicate that Euglena chloroplast lamellae show this cyclic electron transport only as an artifact due to the isolation procedure. The results furthermore indicate that the pteridine-like, fluorescent compound No. 4 is not active as the primary electron acceptor of photosystem I; it may however be involved in oxygen activation by Euglena gracilis chloroplasts. 相似文献
17.
The effect of indoleacetic acid, gibberellic acid, 2,4-dichloro-phenoxyacetic acid and amitrole at various concentration levels ranging from 0.05 to 1.0 mM on the photosynthetic evolution of O2 and 14CO2 fixation by isolated leaf cells was studied. The plant growth regulators enhanced O2 evolution and 14CO2 fixation at low concentrations and were inhibitory beyond a critical level. The amitrole had an inhibitory effect at all the concentration levels used. All the substances exhibited similar patterns of effect on the ferricyanide reduction by isolated chloroplasts and on the electron transport rates of sub-chloro-plast particles containing PS-I and PS-II independently, under non-phosphorylating conditions. As was seen from the response in all the three electron transport systems of the chloroplast studied, the electron transport chain connecting PS-II and PS-I could be considered as a possible site of action at least for the growth regulating substances as it is the only part that is common to all the three reactions. The phosphorylation associated with this part of the electron transport was “inhibited” by the substances even at the lowest concentration used. The stimulation of non-phosphorylating electron flow, with a simultaneous reduction in the rate of ATP synthesis, at low concentration levels indicated that these substances played a possible uncoupling role. The amitrole on the other hand appeared to have a generalized non-specific inhibitory action on all the partial reactions of photosynthesis. 相似文献
18.
Effects of batatasins I, III and V, phenolic growth inhibitors occuring in dormant bulbils of Dioscorea batatas Decne., on photosynthetic reactions of chloroplasts from spinach (Spinacia oleracea L.) and on respiration of mitochondria from potatoes (Solanum tuberosum L.) were investigated. In chloroplasts, the batatasins effectively inhibited CO2-dependent oxygen evolution and electron flow from water to acceptors such as dichlorophenolindophenol, ferricyanide and methylviologen. Photosystem-I dependent electron transport from ascorbate to oxygen was stimulated. The proton conductivity of thylakoid membranes was increased and phosphorylation was uncoupled from electron transport. Inhibition of electron transport with water as electron donor appeared to precede uncoupling. In mitochondrial, batatasin I did not much inhibit succinate-dependent O2 uptake in the absence of ADP, but caused strong inhibition in the presence of ADP. Batatasins III and V inhibited oxygen uptake irrespective of the presence or absence of ADP. Inhibition of chloroplast and mitochondrial reactions by batatasins was shown to be reversible.Abbrevations B-I
batatasin I, 6-hydroxy-2,4,7-trimethoxyphenanthrene
- B-III
batatasin III, 3,3-dihydroxy-5-methoxybibenzyl
- B-V
batatasin V, 2-hydroxy-3,4,5-trimethoxybibenzyl
- Chl
chlorophyll
- MV
methylviologen
- DCPIP
2,6-dichlorophenol-indophenol
- DCMU
3-(3,4-dichlorophenyl)-1,1-dimethylurea
- PVP
polyvinylpyrrolidone 相似文献
19.
Cyanobacterin is a secondary metabolite produced by the cyanobacterium (blue-green alga) Scytonema hofmanni. The compound had previously been isolated and chemically characterized. It was shown to inhibit the growth of algae at a concentration of approximately 5 micromolar. Cyanobacterin also inhibited the growth of angiosperms, including the aquatic, Lemna, and terrestrial species such as corn and peas. In isolated pea chloroplasts, cyanobacterin inhibited the Hill reaction when p-benzoquinone, K3Fe(CN)6, dichlorophenolindophenol, or silicomolybdate were used as electron acceptors. The concentration needed to inhibit the Hill reaction in photosystem II was generally lower than the concentration of the known photosystem II inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethyl urea. Cyanobacterin had no effect on electron transport in photosystem I. The data indicate that cyanobacterin inhibits O2 evolving photosynthetic electron transport in all plants and that the most probable site of action is in photosystem II. 相似文献
20.
Water stress inhibited the photosynthetic O2 evolution rate of wheat leaves. It was shown that water stress decreased the electron transport rate, the activities of photophosphorylation and, coupling factor, and, the synthesis of ATP in chloroplasts. PS Ⅱ electron transport was more senstitive to water stress than PS Ⅰ. The reduction in photophosphorylation activity might be the results of reduction in electron transport rate and coupling factor activity, as well as the uncoupling effect of water stress on chloroplasts. The uncoupling effect could be due to the inhibition of light induced proton translocation in chloroplasts. 相似文献