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1.
The influence of vanadium compounds (vanadate, vanadyl citrate) on photosynthesis in Chlorella fusca and in algal and spinach chloroplasts has been investigated. It was found that: 1. At moderately high concentrations (at least 0.1 mM) both vanadate and vanadyl citrate enhance photosynthetic O2 production in intact C. fusca cells. At lower V concentration (about 2 μM) only vanadate stimulates photosynthesis. The increase is dependent on culture conditions and on light intensity. 2. Up to 1 mM V, neither vanadium compound influences PS II activity, either in intact cells or in algal or spinach chloroplasts. 3. The PS I reaction in algal and spinach chloroplasts is maximally enhanced (3-fold) in presence of vanadium (20 μM). The increase is independent of light intensity. 4. Cr(VI), Mo(VI), and W(VI) (1 mM) stimulate photosynthesis in intact C. fusca cells, but do not influence the photosystems of isolated chloroplasts. Vanadium is suggested to act as a redox catalyst in the electron transport from PS II to PS I. 相似文献
2.
The ratio of Photosystem (PS) II to PS I electron-transport capacity in spinach chloroplasts was compared from reaction-center and steady-state rate measurements. The reaction-center electron-transport capacity was based upon both the relative concentrations of the PS IIα, PS IIβ and PS I centers, and the number of chlorophyll molecules associated with each type of center. The reaction-center ratio of total PS II to PS I electron-transport capacity was about 1.8:1. Steady-state electron-transport capacity data were obtained from the rate of light-induced absorbance-change measurements in the presence of ferredoxin-NADP+, potassium ferricyanide and 2,5-dimethylbenzoquinone (DMQ). A new method was developed for determining the partition of reduced DMQ between the thylakoid membrane and the surrounding aqueous phase. The ratio of membrane-bound to aqueous DMQH2 was experimentally determined to be 1.3:1. When used at low concentrations (200 μM), potassium ferricyanide is shown to be strictly a PS I electron acceptor. At concentrations higher than 200 μM, ferricyanide intercepted electrons from the reducing side of PS II as well. The experimental rates of electron flow through PS II and PS I defined a PS II/PS I electron-transport capacity ratio of 1.6:1. 相似文献
3.
Thylakoids prepared from spinach (Spinacea oleracea L.) chloroplasts were exposed to osmotic stress in vitro in the presence or absence of different inorganic salts. By an hour after incubation in 1.0 M sorbitol and 10 mM (or more) MgCl2, the thylakoids lost approximately 80% of their photosystem (PS) II activity, but not PS I. The inhibition occurred only in presence of magnesium as indicated by the combinations of several cations/anions. The PS II activity was relatively insensitive to osmotic stress in the presence of diphenyl carbazide. We therefore conclude that under conditions of water stress in the presence of 10 mM or higher Mg2+, the oxygen evolving system in chloroplasts is rapidly inactivated.Abbreviations DCMU
3(3,4-dichlorophenyl)-1,1-dimethylurea
- DCPIP
2,6-dichlorophenol indophenol
- DPC
diphenyl carbazide
- MV
methyl viologen
- PS
photosystem
Part of this work was included in the thesis submitted by the first author of M.Phil.degree. 相似文献
4.
EGTA, a calcium chelator, inhibits electron transport in photosystem II of spinach chloroplasts at two different sites 总被引:2,自引:0,他引:2
A fifteen minute incubation of spinach chloroplasts with the divalent Ca2+ chelator, EGTA, in concentrations 50–250 μM, inhibits electron transport through both photosystems. All photosystem II partial reactions, including indophenol, ferricyanide and the DCMU-insensitive silicomolybdate reduction are inhibited from 70–100%. The photosystem II donor reaction, diphenyl carbazide → indophenol, is also inhibited, indicating that the inhibition site comes after the Mn2+ site, and that the first Ca2+ effect noted (site II) is not on the water oxidation enzyme, as is commonly assumed, but between the Mn2+ site and plastoquinone A pool. The other photosystem II effect of EGTA (Ca2+ site I), occurs in the region between plastoquinone A and P700 in the electron transport chain of chloroplasts. About 50% inhibition of the reaction ascorbate + TMPD → methyl viologen is given by incubation with 200 μM EGTA for 15 min. Ca2+ site II activity can be restored with 20 mM CaCl2. Ca2+ site I responds to Ca2+ and plastocyanin added jointly. More than 90% activity in the ascorbate + TMPD → methylviologen reaction can be restored. Various ways in which Ca2+ ions could affect chloroplast structure and function are discussed. Since EGTA is more likely to penetrate chloroplast membranes than EDTA, which is known to remove CF1, the coupling factor, from chloroplast membranes, and since Mg2+ ions are ineffective in restoring activity, it is concluded that Ca2+ may function in the electron transport chain of chloroplasts in a hitherto unsuspected manner. 相似文献
5.
The structural-functional organization of higher plant chloroplasts has been investigated in relation to the particular light conditions during plant growth. (1) Light intensity variations during growth caused changes in the ratio, in the light-saturated uncoupled rates of electron transport to a Hill oxidant and in the distribution of the chloroplast volume between the membrane and stroma phases. (2) Light quality differences during growth had an effect on the PS II/PS I reaction center ratio and on the chloroplast membrane phase differentiation into grana and stroma thylakoids. Plants grown under far-red-enriched (680–710 nm) illumination contained higher (20–25%) amounts of PS II and simultaneously lower (20–25%) amounts of PS I reaction centers. They also showed a higher grana density along with thicker grana stacks in their chloroplasts. (3) The size of the light-harvesting antenna pool of PS II centers was estimated from the fluorescence time course of 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea-poisoned chloroplasts and was found to be fairly constant (±10%) in spite of the variable PS II/PS I reaction center ratio. The results are compatible with the hypothesis that the structural entities of grana facilitated the centralization and relative concentration increase of a certain group of PS II reaction centers. 相似文献
6.
Chloroplasts developed at cold-hardening (5°C) and non-hardening temperatures (20°C) were compared with respect to the stability of photosynthetic electron transport activities, the capacity to produce and maintain a H+ gradient and the capacity fat photophosphorylation as a function of resuspension in the presence or absence of osmoticum. The results for electron transport indicate that whole chain, photosystem I and pfaotosystem II activities in non-hardened chloroplast thyalkoids were unaffected by resuspension in the presence of high or low osmoticum. In contrast, the same electron transport activities in cold-hardened chloroplast thylakoids exhibited a 3- to 4-fold decrease in activity when resuspended in the presence of low osmoticum. Impairment of electron transport through photosystem II of cold-hardened thylakoids resuspended in the presence of low osmoticum was supported by room temperature fluorescence induction kinetics. Since the presence of Mn2+ partially overcame this inhibition, it is concluded that this osmotically-induced inhibition of PSII activity in cold-hardened chloroplast thylakoids may, in part, be due to damage to the H2O-splitting side of photosystem II. Both the initial rate and the maximum capacity for cyclic photophosphorylation were significantly inhibited in cold-hardened as compared to non-hardened thylakoids upon resuspension in the presence of low concentrations of osmoticum. This was correlated with an inability of the cold-hardened chloroplast thylakoids to maintain a significant transrnembrane H+ gradient. The results indicate that cold-hardened thylakoid membranes required an osmotic concentration (0.8 M) twice as high as non-hardened thylakoids (0.4 M) to produce the same initial rate of H+ uptake. In addition, the capacity to produce a proton gradient in cold-hardened thylakoids was less stable than that in non-hardened thylakoids regardless of the osmotic concentration tested. It is concluded that development of rye thylakoid membranes at low temperature results in a differential sensitivity to low osmoticum and thus extreme caution should be exercised when comparing the structure and function of isolated thylakoids developed under contrasting thermal regimes. 相似文献
7.
The effects of protein phosphorylation and cation depletion on the electron transport rate and fluorescence emission characteristics of photosystem I at two stages of chloroplast development in light-grown wheat leaves are examined. The light-harvesting chlorophyll a/b protein complex associated with photosystem I (LHC I) was absent from the thylakoids at the early stage of development, but that associated with photosystem II (LHC II) was present. Protein phosphorylation produced an increase in the light-limited rate of photosystem I electron transport at the early stage of development when chlorophyll b was preferentially excited, indicating that LHC I is not required for transfer of excitation energy from phosphorylated LHC II to the core complex of photosystem I. However, no enhancement of photosystem I fluorescence at 77 K was observed at this stage of development, demonstrating that a strict relationship between excitation energy density in photosystem I pigment matrices and the long-wavelength fluorescence emission from photosystem I at 77 K does not exist. Depletion of Mg2+ from the thylakoids produced a stimulation of photosystem I electron transport at both stages of development, but a large enhancement of the photosystem I fluorescence emission was observed only in the thylakoids containing LHC I. It is suggested that the enhancement of PS I electron transport by Mg2+-depletion and phosphorylation of LHC II is associated with an enhancement of fluorescence at 77 K from LHC I and not from the core complex of PS I. 相似文献
8.
Light-induced Fourier transformed infrared (FTIR) difference spectroscopy is a powerful method to study the structures and reactions of redox cofactors involved in the photosynthetic electron transport chain. So far, most of the FTIR studies of the reactions of oxygenic photosynthesis have been performed using isolated photosystem I (PSI) and photosystem II (PSII) preparations, which, however, could be modified during isolation procedures. In this study, we developed a methodology to evaluate the photosynthetic activities of thylakoids using FTIR spectroscopy. FTIR difference spectra upon successive flashes using thylakoids from spinach exhibited signals typical of the S-state cycle at the Mn4CaO5 cluster and QB reactions in PSII with period-four and -two oscillations, respectively. Similar measurement in the presence of an artificial quinone as an exogenous electron acceptor showed features specific to the S-state cycle. Simulations of the oscillation patterns provided the quantum efficiencies of the S-state cycle and electron transfer in PSII. Moreover, FTIR measurement under continuous illumination on thylakoids in the presence of DCMU showed signals due to QA reduction and P700 oxidation simultaneously. From the relative amplitudes of marker bands of QA? and P700+, the molar ratio of photoactive PSII and PSI centers in thylakoids was estimated. FTIR analyses of the photo-reactions in thylakoids, which are more intact than isolated photosystems, will be useful in investigations of the photosynthetic mechanism especially by genetic modification of photosystem proteins. 相似文献
9.
Redox titration of the electrochromic carotenoid band shift, detected at 50 μs after a saturating actinic flash, in spinach chloroplasts, shows that only one electron acceptor in Photosystem II participates in a transmembrane primary electron transfer. This species, the primary quinone acceptor, Q, shows only one midpoint potential (Em,7.5) of approx. 0 V and is undoubtedly equivalent to the fluorescence quencher, QH. A second titration wave is observed at low potential () and at greater than 3 ms after a saturating actinic flash. This wave has an action spectrum different from that of Photosystem II centers containing Q and could arise from a secondary but not primary electron transfer. A low-potential fluorescence quencher is observed in chloroplasts which largely disappears in a single saturating flash at ? 185 mV and which does not participate in a transmembrane electron transfer. This low-potential quencher (probably equivalent to fluorescence quencher, QL) and Q are altogether different species. Redox titration of C550 shows that if electron acceptor Qβ is indeed characterized by an Em,7 of + 120 mV, then this acceptor does not give rise to a C550 signal upon reduction and does not participate in a transmembrane electron transfer. This titration also shows that C550 is not associated with QL. 相似文献
10.
Adam J. Bell Laurie K. Frankel Terry M. Bricker 《The Journal of biological chemistry》2015,290(30):18429-18437
Styrene-maleic acid copolymer was used to effect a non-detergent partial solubilization of thylakoids from spinach. A high density membrane fraction, which was not solubilized by the copolymer, was isolated and was highly enriched in the Photosystem (PS) I-light-harvesting chlorophyll (LHC) II supercomplex and depleted of PS II, the cytochrome b6/f complex, and ATP synthase. The LHC II associated with the supercomplex appeared to be energetically coupled to PS I based on 77 K fluorescence, P700 photooxidation, and PS I electron transport light saturation experiments. The chlorophyll (Chl) a/b ratio of the PS I-LHC II membranes was 3.2 ± 0.9, indicating that on average, three LHC II trimers may associate with each PS I. The implication of these findings within the context of higher plant PS I antenna organization is discussed. 相似文献
11.
Pea chloroplasts were treated with phospholipase A2 which hydrolysed approx. 75% phosphatidylglycerol and 60% phosphatidylcholine. The major effect of the treatment was an inhibition of Photosystem (PS) II electron transport together with an (approx. 30%) increase of initial chlorophyll fluorescence (F0) and a subsequent loss of variable fluorescence during induction, as well as an inhibition of the cation-induced rise in steady-state chlorophyll fluorescence. In contrast to the effects upon PS II activities, PS I activity was not depressed and increased slightly under certain conditions, while the coupling factor for photophosphorylation was inhibited to some extent. No significant increase in spillover was observed following the treatment with phospholipase A2. These results are discussed in relation to the ways in which phospholipid depletion may lead to the various effects observed. It is proposed that the site of PS II inhibition after phospholipase A2 treatment may be at the electron transfer from pheophytin to Q, the first quinone-type electron acceptor. 相似文献
12.
Single-photon timing with picosecond resolution is used to investigate the effect of Mg2+ on the room-temperature fluorescence decay kinetics in broken spinach chloroplasts. In agreement with an earlier paper (Haehnel, W., Nairn, J.A., Reisberg, P. and Sauer, K. (1982) Biochim. Biophys. Acta 680, 161–173), we find three components in the fluorescence decay both in the presence and in the absence of Mg2+. The behavior of these components is examined as a function of Mg2+ concentration at both the F0 and the Fmax fluorescence levels, and as a function of the excitation intensity for thylakoids from spinach chloroplasts isolated in the absence of added Mg2+. Analysis of the results indicates that the subsequent addition of Mg2+ has effects which occur at different levels of added cation. At low levels of Mg2+ (less than 0.75 mM), there appears to be a decrease in communication between Photosystem (PS) II and PS I, which amounts to a decrease in the spillover rate between PS II and PS I. At higher levels of Mg2+ (about 2 mM), there appears to be an increase in communication between PS II units and an increase in the effective absorption cross-section of PS II, probably both of these involving the chlorophyll light-harvesting antenna. 相似文献
13.
S S Tong Y Hirokata M A Trush E G Mimnaugh E Ginsburg M C Lowe T E Gram 《Biochemical and biophysical research communications》1981,100(3):944-950
The photosystem II electron acceptor 3,6-dichloro-2,5-dimethoxy-p-benzoquinone [DCDMQ] is suggested to replace the second quinone-type two electron acceptor B (or R); the DCDMQ Hill reaction is sensitive to 3-(3,4-dichlorophenyl)-1,1-dimethylurea, but is insensitive to dry heptane extraction of thylakoids and other photosystem II inhibitors. Addition of HCO3? to CO2-depleted thylakoids in silicomolybdate, DCDMQ, diaminodurene and ferricyanide Hill reactions brought about 1,3,10 and 10 fold increase in the electron transport rates; these data confirm that HCO3? affects both Q? to B and B2? to PQ reactions. 相似文献
14.
Inhibition of photosynthesis by UV-B was investigated in the thalloid liverwort Conocephalum conicum Dum. UV-B irradiance was adjusted to a strength producing 50% inhibition of the rate of photosynthesis during 10 min of irradiation. A linear relationship of the fluorescence terms Fv/Fm of photosystem (PS) II and JP was observed following a UV-B irradiation. This suggested that PS II was a major site of UV-B-induced damage of photosynthesis. The apparent inhibition of Fv/Fm was much smaller when electron flow to the secondary PS II acceptor QB was inhibited by DCMU or when Fv/Fm was measured at 77 K. Apparently, the major target of UV-B effects was electron donation to the PS II reaction center, rather than electron transfer reactions at the PS II acceptor side. The time required for repair of PS II from UV-B-induced damage was light-dependent and minimal at a flux density of 5 μE m?2 s?1. Low temperatures and the presence of streptomycin inhibited the repair processes of PS II, indicating that protein synthesis may be involved in the recovery of PS II. The data indicate that UV-B irradiation on bright and cool winter days may be most harmful for photosynthesis of C. conicum. A repeated irradiation of the thalli with UV-B induced tolerance of photosynthesis which was related to an accumulation of pigments with a maximum of absorption around 315 nm. 相似文献
15.
The organization of the electron transport components in mesophyll and bundle sheath chloroplasts of Zea mays was investigated. Grana-containing mesophyll chloroplasts (chlorophyll a to chlorophyll b ratio of about 3.0) possessed the full complement of the various electron transport components, comparable to chloroplasts from C3 plants. Agranal bundle sheath chloroplasts () contained the full complement of photosystem (PS) I and of cytochrome (cyt) f but lacked a major portion of PS II and its associated Chl light-harvesting complex (LHC), and most of the cyt b559. The kinetic analysis of system I photoactivity revealed that the functional photosynthetic unit size of PS I was unchanged and identical in mesophyll and bundle sheath chloroplasts. The results suggest that PS I is contained in stroma-exposed thylakoids and that it does not receive excitation energy from the Chl LHC present in the grana. A stoichiometric parity between PS I and cyt f in mesophyll and bundle sheath chloroplasts indicates that biosynthetic and functional properties of cyt f and P700 are closely coordinated. Thus, it is likely that both cyt f and P700 are located in the membrane of the intergrana thylakoids only. The kinetic analysis of PS II photoactivity revealed the absence of PS IIαfrom the bundle sheath chloroplasts and helped identify the small complement of system II in bundle sheath chloroplasts as PS IIβ. The distribution of the main electron transport components in grana and stroma thylakoids is presented in a model of the higher plant chloroplast membrane system. 相似文献
16.
Nikitishena OV Smolova TN Khatypov RA Shkuropatov AJ Klimov VV 《Biochemistry. Biokhimii?a》2002,67(3):364-371
A new pathway of photoinactivation of photosystem II (PS II) connected with irreversible photoaccumulation of reduced pheophytin (Ph) in isolated D1–D2–cytochrome b
559 complexes of reaction center (RC) of PS II was discovered. The inhibitory effects of white light illumination on photochemical activity of D1–D2–cytochrome b
559 complexes of RCs of photosystem II, isolated from pea chloroplasts, have been compared under anaerobic conditions in the absence and in the presence of sodium dithionite, electron transfer from which to the oxidized primary electron donor P680+ results in the photoaccumulation of anion-radical of the primary electron acceptor, PH. In both cases, prolonged illumination (1-5 min, 120 W/m2) led to a pronounced loss of the photochemical activity as it was monitored by measuring the amplitude of the reversible photoinduced absorbance changes at 682 nm related to the photoreduction of Ph. The extent of the photoinactivation depended on the illumination time and pH of the medium. At pH 8.0, the presence of dithionite during photoinactivation brought about a protective effect compared to that in a control sample. In contrast, lowering pH to 6.0 increased the sensitivity to photoinactivation in the dithionite containing samples. For 5 min irradiation, the photochemical activity in the absence and in the presence of dithionite decreased by 35 and 72%, respectively (this was accompanied by an irreversible bleaching of the pheophytin Qx absorption band at 542 nm). Degradation of the D1 and D2 proteins was not observed under these conditions. A subsequent addition of an electron acceptor, potassium ferricyanide, to the illuminated samples restored neither the amplitude of the signal at 682 nm nor absorption at 542 nm. It is suggested that at pH < 7.0 the photoaccumulated PH is irreversibly converted into a secondary, most probably protonated form, that does not lead to destruction of the RCs but prevents the photoformation of the primary radical pair [P680+PH]. A possible application of this effect to photoinactivation of PS II in vivo is discussed. 相似文献
17.
In order to characterize the photosystem II (PS II) centers which are inactive in plastoquinone reduction, the initial variable fluorescence rise from the non-variable fluorescence level Fo to an intermediate plateau level Fi has been studied. We find that the initial fluorescence rise is a monophasic exponential function of time. Its rate constant is similar to the initial rate of the fastest phase (-phase) of the fluorescence induction curve from DCMU-poisoned chloroplasts. In addition, the initial fluorescence rise and the -phase have the following common properties: their rate constants vary linearly with excitation light intensity and their fluorescence yields are lowered by removal of Mg++ from the suspension medium. We suggest that the inactive PS II centers, which give rise to the fluorescence rise from Fo to Fi, belong to the -type PS II centers. However, since these inactive centers do not display sigmoidicity in fluorescence, they thus do not allow energy transfer between PS II units like PS II.Abbreviations DCMU
3-(3,4-dichlorophenyl)-1,1-dimethyl urea
- DMQ
2,5-dimethyl-p-benzoquinone
- Fo
initial non-variable fluorescence yield
- Fm
maximum fluorescence yield
- Fi
intermediate fluorescence yield
- PS II
photosystem II
- QA
primary quinone acceptor of PS II
- QB
secondary quinone acceptor of PS II 相似文献
18.
The electron-transfer reactions between the plastoquinone molecules of the acceptor side of photosystem II have been inferred to be regulated by a proteinaceous component (apoenzyme), which additionally contains the receptor site for DCMU-type inhibitors (Renger, G., (1976) Biochim. Biophys. Acta 440, 287–300). In order to reveal the functional properties of this apoenzyme, the effect of procedures which modify the structure of proteins on the photosystem II electron transport have been investigated in isolated spinach chloroplasts by comparative measurements of O2 evolution and absorption changes at 334 nm induced by repetitive flash excitation and of fluorescence induction curves caused by continuous actinic light. It was found that: (1) The release of blockage of O2 evolution by the DCMU-type inhibitor SN 58132 due to mild tryptic digestion correlates kinetically with the deterioration of the binding properties. (2) Glutaraldehyde fixation of chloroplasts does not markedly modify the reoxidation kinetics of the reduced primary plastoquinone acceptor component, X320?, of photosystem II, but it greatly reduces the fluorescence yield of the antenna chlorophylls and slightly retards the ADRY effect. Furthermore, it prevents the attack of trypsin on the apoenzyme. (3) Incubation of chloroplasts in ‘low’ salt medium markedly diminishes the ability of trypsin to release the blockage of O2 evolution by SN 58132 and completely presents the effect on inhibition by DCMU. Based on these results and taking into account recent findings of other groups, the functional mechanism of the electron transport on the acceptor side of photosystem II is discussed. Assuming a tunnel mechanism, the apoprotein is inferred to act as a dynamic regulator rather than changing only the relative levels of the redox potentials of the plastoquinone molecules involved in the transfer steps. It is further concluded that salt depletion does not only cause grana unstacking and a change of the excitation energy transfer probabilities, but it additionally modifies the orientation of functional membrane proteins of photosystem II and their structural interaction within the thylakoid membrane. 相似文献
19.
1. Photosystem I particles enriched in P-700 prepared by Triton X-100 treatment of chloroplasts show a light-induced increase in fluorescence yield of more than 100% in the presence of dithionite but not in its absence.2. Steady state light maintains the P-700, of these particles, in the oxidised state when ascorbate is present but in the presence of dithionite only a transient oxidation occurs.3. EPR data show that, in these particles, the primary electron acceptor (X) is maintained in the reduced state by light at room temperature only when the dithionite is also present. In contrast, the secondary electron acceptors are reduced in the dark by dithionite.4. Fluorescence emission and excitation spectra and fluorescence lifetime measurements for the constant and variable fluorescence indicate a heterogeneity of the chlorophyll in these particles.5. It is concluded that the variable fluorescence comes from those chlorophylls which can transfer their energy to the reaction centre and that the states PX and P+X are more effective quenchers of chlorophyll fluorescence than PX?, where P is P-700. 相似文献
20.
Baker NR 《Plant physiology》1978,62(6):889-893
The effects of wide concentration ranges of NaCl, KCl, and MgCl2 on ferricyanide reduction and the fluorescence induction curve of isolated spinach (Spinacia oleracea) chloroplasts were investigated. Concentrations of the monovalent salts above 100 mm and MgCl2 above 25 mm produced a decrease in the rate of ferricyanide reduction by thylakoids uncoupled with 2.5 mm NH4Cl which cannot be attributed to changes in the primary photochemical capacity of photosystem II. Salt-induced decreases in the effective concentration of the secondary electron acceptor of photosystem II, plastoquinone, reduce the capacity for secondary photochemistry of photosystem II and this could contribute to the reduction in ferricyanide reduction by uncoupled thylakoids at high salinities. The rate of ferricyanide reduction by coupled thylakoids is little affected by salinity changes, indicating that the rate-limiting phosphorylation mechanism in electron flow from water to ferricyanide in coupled thylakoids is salt-tolerant, whereas the rate-limiting reaction in uncoupled ferricyanide reduction is considerably affected by salinity changes. Salt-induced changes in the fluorescence induction curve are interpreted in terms of changes in the rate constants for excitation decay by radiationless transitions, exciton transfer from photosystem II chlorophylls to other associated chlorophyll species, and photochemistry. 相似文献