Changes in the photochemical activities, influenced by variation in the growth light intensity, were followed in typical C3 (Phaseolus, Ipomoea) and C4 (Amaranthus, Sorghum) plants. Progressive decrease in the growth light intensity accelerated the O-P fluorescence induction in whole leaves. Such acceleration of the fluorescence kinetics was found to be not due to enhanced photosystem II activity but possibly a result of reduced rate of electron flow between the two photosystems. This is supported by 4 lines of evidence: (1) by the Hill activity determined in the presence of electron acceptors functioning before and after plastoquinone; (2) the photosynthetic unit size determined after flash excitation showing variations that were apparently too small to account for the changes observed fluorescence induction; (3) modification of the kinetics of secondrange light-induced absorbance changes at 520 nm; and (4) absence of significant changes in the ratio of P700/total chlorophyll ratio. The P700/cytochrome f ratio, however, increased from the usual 1–1.5 to 3–4 in plants grown under 9% sunlight. Increase in the P700/cytochrome f ratio was found to be due to a decrease in the cytochrome f/chlorophyll ratio, and this was due to perhaps to a simultaneous increase in chlorophyll and decrease in cytochrome content. 相似文献
The induction kinetics of the 680 nm chlorophyll fluorescence were measured on attached leaves of Kalanchoë daigremontiana R. Hamet et Perr. (CAM plant), Sedum telephium L. and Sedum spectabile Bor. (C3 plant in spring, CAM plant in summer) and Raphanus sativus L. (C3 plant) at three different times during a 12/12h day/night cycle. During the fluorescence transient the fluorescence intensity at the O, P and T-level (fO, fmax, fst,) was different for the plant species tested; this may be due to their different leaf structure, pigment composition and organization of their photosystems. The kinetics of the fluorescence induction depended on the time of preillumination or dark adaptation during the light/dark cycle but not on the type of primary CO2 fixation mechanism (C3 and CAM). For dark adapted leaves measured either at the end of the dark phase or after dark adaptation of plants taken from the light phase a higher P-level fluorescence, a higher variable fluorescence (P-O) and a larger complementary area were found than for leaves of plants taken directly from the light phase. This indicates the presence of largely oxidized photosystem 2 acceptor pools during darkness. During the light phase the fluorescence decline after the P-level was faster than during the dark phase; from this we conclude that the light adaptation of the photosynthetic apparatus (state 1→ state 2 transition, Δ pH) during the induction period proceeded faster in plants taken from the light phase than in plants taken from the dark phase. 相似文献
Reduction kinetics of cytochrome f, plastocyanin (PC) and P700 (‘high-potential chain’) in thylakoids from spinach were followed after pre-oxidation by a saturating light pulse. We describe a novel approach to follow PC redox kinetics from deconvolution of 810-860 nm absorption changes. The equilibration between the redox-components was analyzed by plotting the redox state of cytochrome f and PC against that of P700. In thylakoids with (1) diminished electron transport rate (adjusted with a cytochrome bf inhibitor) or (2) de-stacked grana, cytochrome f and PC relaxed close to their thermodynamic equilibriums with P700. In stacked thylakoids with non-inhibited electron transport, the equilibration plots were complex and non-hyperbolic, suggesting that during fast electron flux, the ‘high-potential chain’ does not homogeneously equilibrate throughout the membrane. Apparent equilibrium constants <5 were calculated, which are below the thermodynamic equilibrium known for the ‘high potential chain’. The disequilibrium found in stacked thylakoids with high electron fluxes is explained by restricted long-range PC diffusion. We develop a model assuming that about 30% of Photosystem I mainly located in grana end-membranes and margins rapidly equilibrate with cytochrome f via short-distance transluminal PC diffusion, while long-range lateral PC migration between grana cores and distant stroma lamellae is restricted. Implications for the electron flux control are discussed. 相似文献
It has been proposed that Fe stress may be used in the study of limiting factors in photosynthesis as an experimental means of varying photochemical capacity in vivo (Plant Physiol 1980 65: 114-120). In this paper the effect of Fe stress on photosynthetic unit number, size, and composition was investigated by measuring P700, cytochrome (Cyt) f, chlorophyll (Chl) a, and Chl b in sugar beet leaves. The results show that when Fe stress reduced Chl per unit area by 80% (from 60 to 12 micrograms per square centimeter), it decreased the number of P700 molecules per unit area by 88% and Cyt f per unit area by 86%; over the same range the Chl to P700 ratio increased by 37% but there was no significant change in the Chl to Cyt f ratio. These data suggest that Fe stress decreases photochemical capacity and Chl per unit area by diminishing the number of photosynthetic units per unit leaf area. 相似文献
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
Representative plants containing either the reductive pentose phosphate cycle or the C4 dicarboxylic acid cycle of photosynthetic carbon dioxide fixation have distinctly different contents of P700 and chlorophylls a and b. With leaf extracts and isolated chloroplasts from C4 cycle plants, the mean value of the relative ratio of P700 to total chlorophyll was 1.83 and the mean value of the ratio of chlorophyll a to b was 3.89. The respective values in similar extracts and chloroplasts from pentose cycle plants are 1.2 and 2.78. 相似文献
Membrane development in chloroplasts was explored by resupplying iron to iron-deficient sugar beet (Beta vulgaris L. cv F58-554H1) and monitoring changes in lamellar components during regreening. The synthesis of chlorophyll a, chlorophyll b, and Q, the first stable electron acceptor of photosystem II, exhibited a lag phase during the first 24 to 48 hours of resupply. In contrast, the per area amounts of P700 and cytochrome f increased linearly over the first 48 hours. During the early regreening period, the Q to P700 ratio was 2.6 and decreased to 0.7 after 96 hours of regreening. The rate of photosynthesis (net CO2 uptake) per chlorophyll increased during the first 48 hours of resupply, then by 96 hours decreased to values typical of control plants. The results suggest that there was preferential synthesis of the measured photosystem I components during the first 24 to 48 hours, while from 48 to 96 hours there was rapid synthesis of all components. The iron nutrition-mediated chloroplast development system provides a useful experimental approach for studying biomembrane synthesis and structural-functional relations of the photosynthetic apparatus. 相似文献
Treatment of isolated chloroplasts with high-energy pulses of the ruby laser causes graded structural changes in the chloroplast membranes and is here correlated with the biochemical changes produced. The laser treatment caused decreases in the photoinducible absorption changes of cytochromes b559, b563, and P520 (the carotenoid shift), but smaller decreases in cytochrome f. The decreases correlated with the quantum efficiency alterations produced by the laser treatment. Ferricyanide photoreduction and O2 evolution was only slightly affected by the laser treatment. The slow phase of the dark recovery kinetics of P520 was increased maximally by the lowest laser input energies and NADP+ photoreduction induced by carbonylcyanide-P-trifluoromethoxyphenylhydrazone (FCCP) was decreased maximally by the lowest energies, suggesting that uncoupling of the chloroplasts was the most sensitive parameter. This was corroborated by our previous observation (5) that chloroplast membrane bound surface particles (coupling factor) was the ultrastructural change most sensitive to the laser pulses. Electron flow from photosystem II to photosystem I was not altered by the laser treatment. The laser treatments did not cause a detectable decrease in total chlorophyll in the chloroplasts, however, approximately 10% of the total chlorophyll was present in the solution phase after the treatment, whereas no detectable cytochromes were present in the solution phase. 相似文献
Absorbance changes in the region 500–565 nm and at 702 nm, brought about by excitation of Photosystems 1 and 2, respectively, were measured in spinach chloroplasts at ?50 °C. Either dark-adapted chloroplasts were used or chloroplasts preilluminated with a number of short saturating flashes just before cooling.Both photosystems were found to cause a light-induced increase of absorbance at 518 nm (due to “P518”). The System 1-induced change was not affected by preillumination. It decayed within 1 s in the dark and showed similar kinetics as P700. Experiments in the presence of external electron acceptors (methylviologen or Fe(CN)63?) suggested that P518 was not affected by the redox state of the primary electron acceptor of System 1. The absorbance increase at 518 nm due to System 2 decayed in the dark with a half-time of several min. The kinetics were similar to those of C-550, the presumed indicator of the primary electron acceptor of System 2. After two flashes preillumination the changes due to P518 and C-550 were reduced by about 40%, and a relatively slow, System 2-induced oxidation of cytochrome b559 occurred which proceeded at a similar rate as the increase in yield of chlorophyll a fluorescence. The results indicate that at ?50°C two different photoreactions of System 2 occur. One consists of a photoreduction of the primary electron acceptor associated with C-550, accompanied by the oxidation of an unknown electron donor; the other is less efficient and results in the photooxidation of cytochrome b559. 相似文献
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
Isolated mesophyll cells and bundle sheath cells of Digitaria sanguinalis were used to study the light-absorbing pigments and electron transport reactions of a plant which possesses the C4-dicarboxylic acid cycle of photosynthesis. Absorption spectra and chlorophyll determinations are presented showing that mesophyll cells have a chlorophyll a-b ratio of about 3.0 and bundle sheath cells have a chlorophyll a-b ratio of about 4.5. The absorption spectrum of bundle sheath cells has a greater absorption in the 700 nm region at liquid nitrogen temperature, and there is a relatively greater amount of a pigment absorbing at 670 nm in the bundle sheath cells compared to the mesophyll cells. Fluorescence emission spectra, at liquid nitrogen temperature, of mesophyll cells have a fluorescence 730 nm-685 nm ratio of about 0.82 and bundle sheath cells have a ratio of about 2.84. The reversible light-induced absorption change in the region of P700 absorption is similar in both cell types but bundle sheath cells exhibit about twice as much total P700 change as mesophyll cells on a total chlorophyll basis. The delayed light emission of bundle sheath cells is about one-half that of mesophyll cells. Both mesophyll cells and bundle sheath cells evolve oxygen in the presence of Hill oxidants with the mesophyll cells exhibiting about twice the activity of bundle sheath cells, and both activities are inhibited by 1 μM 3-(3,4-dichlorophenyl)-1, 1-dimethylurea. Ferredoxin nicotinamide adenine dinucleotide phosphate reductase is present in both cells although it is about 3- or 4-fold higher in mesophyll cells than in bundle sheath cells. Glyceraldehyde 3-P dehydrogenases, both nicotinamide adenine dinucleotide and nicotinamide adenine dinucleotide phosphate, are equally distributed in the two cell types on a chlorophyll basis. Malic enzyme is localized in the bundle sheath cells. 相似文献
Kinetics of fluorescence at room temperature, electron transport and photooxidation of P700 and cytochrome f have been studied in chloroplasts isolated from active and winter stressed Pinus silvestris. The winter stress induced block in the electron transport chain between the two photosystems is close to the site of plastoquinone, since winter stress and DCMU caused the same type of inhibition of the reoxidation of the primary electron acceptor Q of photosystem II. No winter inhibition of the electron transport between cytochrome f and P700 was observed. Time course studies of P700 photooxidation in chloroplasts of active and winter stressed pine have shown that the photosynthetic unit size must be about equal in the two types of chloroplasts. An apparent increase of the photosynthetic unit size was induced by winter stress, as revealed by the high chlorophyll/P700 ratio of winter stressed pine. The phenomenon is explained by the formation of photosynthetically inactive chlorophyll. Low-temperature fluorescence emission spectra were recorded when either chlorophyll a (433 nm) or chlorophyll b (477 nm) were preferentially excited. Winter stress induced the formation of a chlorophyll a fraction emitting at 673 nm. This chlorophyll is most likely derived from the chlorophyll a antennae of the two photosystems, and it probably contributes to the photosynthetically inactive pool of chlorophyll in winter stressed pine. The light harvesting chlorophyll a/b complex is relatively resistant to winter stress. 相似文献
The role of iron in regulating light harvesting and photochemical energy conversion processes was examined in the marine unicellular chlorophyte Dunaliella tertiolecta and the marine diatom Phaeodactylum tricornutum. In both species, iron limitation led to a reduction in cellular chlorophyll concentrations, but an increase in the in vivo, chlorophyll-specific, optical absorption cross-sections. Moreover, the absorption cross-section of photosystem II, a measure of the photon target area of the traps, was higher in iron-limited cells and decreased rapidly following iron addition. Iron-limited cells exhibited reduced variable/maximum fluorescence ratios and a reduced fluorescence per unit absorption at all wave-lengths between 400 and 575 nm. Following iron addition, variable/maximum fluorescence ratios increased rapidly, reaching 90% of the maximum within 18 to 25 h. Thus, although more light was absorbed per unit of chlorophyll, iron limitation reduced the transfer efficiency of excitation energy in photosystem II. The half-time for the oxidation of primary electron acceptor of photosystem II, calculated from the kinetics of decay of variable maximum fluorescence, increased 2-fold under iron limitation. Quantitative analysis of western blots revealed that cytochrome f and subunit IV (the plastoquinone-docking protein) of the cytochrome b6/f complex were also significantly reduced by lack of iron; recovery from iron limitation was completely inhibited by either cycloheximide or chloramphenicol. The recovery of maximum photosynthetic energy conversion efficiency occurs in three stages: (a) a rapid (3-5 h) increase in electron transfer rates on the acceptor side of photosystem II correlated with de novo synthesis of the cytochrome b6/f complex; (b) an increase (10-15 h) in the quantum efficiency correlated with an increase in D1 accumulation; and (c) a slow (>18 h) increase in chlorophyll levels accompanied by an increase in the efficiency of energy transfer from the light-harvesting chlorophyll proteins to the reaction centers. 相似文献
Signal I, the EPR signal of P-700, induced by long flashes as well as the rate of linear electron transport are investigated at partial inhibition of electron transport in chloroplasts. Inhibition of plastoquinol oxidation by dibromothymoquinone and bathophenanthroline, inhibition of plastocyanin by KCN and HgCl2, and inhibition by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide are used to study a possible electron exchange between electron-transport chains after plastoquinone. (1) At partial inhibition of plastocyanin the reduction kinetics of P-700+ show a fast component comparable to that in control chloroplasts and a new slow component. The slow component indicates P-700+ which is not accessible to residual active plastocyanin under these conditions. We conclude that P-700 is reduced via complexed plastocyanin. (2) The rate of linear electron transport at continuous illumination decreases immediately when increasing amounts of plastocyanin are inhibited by KCN incubation. This is not consistent with an oxidation of cytochrome f by a mobile pool of plastocyanin with respect to the reaction rates of plastocyanin being more than an order of magnitude faster than the rate-limiting step of linear electron transport. It is evidence for a complex between the cytochrome b6 - f complex and plastocyanin. The number of these complexes with active plastocyanin is concluded to control the rate-limiting plastoquinol oxidation. (3) Partial inhibition of the electron transfer between plastoquinone and cytochrome f by dibromothymoquinone and bathophenanthroline causes decelerated monophasic reduction of total P-700+. The P-700 kinetics indicate an electron transfer from the cytochrome b6 - f complex to more than ten Photosystem I reaction center complexes. This cooperation is concluded to occur by lateral diffusion of both complexes in the membrane. (4) The proposed functional organization of electron transport from plastoquinone to P-700 in situ is supported by further kinetic details and is discussed in terms of the spatial distribution of the electron carriers in the thylakoid membrane. 相似文献
The induction kinetics of the 680 nm chlorophyll fluorescence were measured on attached leaves of Kalanchoë daigremontiana R. Hamet et Perr. (CAM plant), Sedum telephium L. and Sedum spectabile Bor. (C3 plant in spring, CAM plant in summer) and Raphanus sativus L. (C3 plant) at three different times during a 12/12 h day/night cycle. During the fluorescence transient the fluorescence intensity at the O, P and T-level (fO, fmax, fst,) was different for the plant species tested; this may be due to their different leaf structure, pigment composition and organization of their photosystems. The kinetics of the fluorescence induction depended on the time of preillumination or dark adaptation during the light/dark cycle but not on the type of primary CO2 fixation mechanism (C3 and CAM). For dark adapted leaves measured either at the end of the dark phase or after dark adaptation of plants taken from the light phase a higher P-level fluorescence, a higher variable fluorescence (P-O) and a larger complementary area were found than for leaves of plants taken directly from the light phase. This indicates the presence of largely oxidized photosystem 2 acceptor pools during darkness. During the light phase the fluorescence decline after the P-level was faster than during the dark phase; from this we conclude that the light adaptation of the photosynthetic apparatus (state 1state 2 transition, pH) during the induction period proceeded faster in plants taken from the light phase than in plants taken from the dark phase.Abbreviations C3 plant
plant with primary CO2 fixation on ribulose-1,5-bis-phosphate (Calvin-Benson cycle)
- CAM
Crassulacean Acid Metabolism 相似文献
Numbers of the Photosystem I reaction center complexes and the cytochrome b6-f complexes with which a cytochrome c-553 molecule can interact within the limiting time of photosynthetic electron transport were examined by measuring flash-induced absorption changes of P-700, cytochrome c-553 and cytochrome f in the thermophilic cyanobacterium Synechococcus sp. The addition of 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB) did not affect the common 2 ms half-time of P-700, cytochrome c-553 and cytochrome f reduction, which is ascribed to electron transfer from the plastoquinone pool. The inhibitor decreased, however, amounts of the three electron carriers which underwent the 2 ms reduction in the order of cytochrome f, cytochrome c-553 and P-700. On excitation with weak flashes which oxidized only a small fraction of cytochrome c-553 molecules present in cells, P-700 remained in the oxidized state after the flashes was reduced with electrons from the Rieske center or plastoquinone but not from cytochrome c-553. The ratios of cytochrome c-553 to cytochrome f oxidized at various flash intensities were constant and similar to the ratio of the two cytochromes present in cells. It is concluded that cytochrome c-553 cannot exchange electrons with large numbers of the Photosystem I reaction center complexes and the cytochrome b6-f complexes in the limiting time, but has a mobility sufficient to mediate electron transfer between the two complexes, which are present at an unbalanced ratio in Synechococcus cells. 相似文献
P-700, plastocyanin and cytochrome f redox kinetics were measured after one flash, using dark-adapted Chlorella in the presence of hydroxylamine and 3(3,4-dichlorophenyl)-1,1-dimethylurea. Plastocyanin becomes increasingly oxidized with a half-time of 70 μs, then undergoes reduction with a half-time of 7 ms. Cytochrome f oxidation has a sigmoidal time-course and a half-time of 100 μs. Its reduction exhibits a half-time of 4 ms. These results are interpreted in a linear scheme: An equilibrium constant of 2 between cytochrome f and plastocyanin (PC), which contrasts with the large equilibrium constant between PC and P-700 is computed.The presence of cytochrome b6 in a cyclic path around Photosystem I is confirmed under these conditions. 相似文献
Effects of irradiance on photosynthetic characteristics were examined in senescent leaves of rice (Oryza sativa L.). Two irradiance treatments (100 and 20% natural sunlight) were imposed after the full expansion of the 13th leaf through senescence. The photosynthetic rate was measured as a function of intercellular CO2 pressure with a gas-exchange system. The amounts of cytochrome f, coupling factor 1, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), and chlorophyll were determined. The coupling factor 1 and cytochrome f contents decreased rapidly during senescence, and their rates of decrease were much faster from the 20% sunlight treatment than from the full sunlight treatment. These changes were well correlated with those in the photosynthetic rate at CO2 pressure = 600 microbars, but not with those under the ambient air condition (350 microbars CO2) and 200 microbars CO2. This suggested that the amounts of coupling factor 1 and cytochrome f from the full sunlight treatment cannot be limiting factors for the photosynthetic rate at ambient air conditions. The Rubisco content also decreased during senescence, but its decrease from the 20% sunlight treatment was appreciably retarded. However, this difference was not reflected in the photosynthetic rates at the ambient and 200 microbars CO2. This implied that in vivo Rubisco activity may be regulated in the senescent leaves from the 20% sunlight treatment. The chlorophyll content decreased most slowly. In the 20% sunlight treatment, it remained apparently constant with a decline in chlorophyll a/b ratio. These photosynthetic characteristics of the senescent rice leaves under low irradiance were discussed in relation to acclimation of shade plants. 相似文献
We have investigated the possible relationships between the cation-induced and phenazine methosulfate (PMS)-induced fluorescence changes and their relation to light induced conformational changes of the thylakoid membrane.1. In isolated chloroplasts, PMS markedly lowers the quantum yield of chlorophyll a fluorescence (φf) when added either in the presence or the absence of dichloro-phenyldimethylurea (DCMU). In contrast, Mg2+ causes an increase in φf. However, these effects are absent in isolated chloroplasts fixed with glutaraldehyde that retain (to a large extent) the ability to pump protons, suggesting that structural alteration of the membrane—not the pH changes—is required for the observed changes in φf. The PMS triggered decrease in φf is not accompanied by any changes in the emission (spectral) characteristics of the two pigment systems, whereas room temperature emission spectra with Mg2+ and Ca2+ show that there is a relative increase of System II to System I fluorescence.2. Washing isolated chloroplasts with 0.75 mM EDTA eliminates (to a large extent) the PMS-induced quenching and Mg2+-induced increase of φf, and these effects are not recovered by the further addition of dicyclohexyl carbodiimide. It is known that washing with EDTA removes the coupling factor, and thus, it seems that the coupling factor is (indirectly) involved in conformational change of thylakoid membranes leading to fluorescence yield changes.3. In purified pigment System II particles, neither PMS nor Mg2+ causes any change in φf. Our data, taken together with those of the others, suggest that a structural modification of the thylakoid membranes (not macroscopic volume changes of the chloroplasts) containing both Photosystems I and II is necessary for the PMS-induced quenching and Mg2+-induced increase of φf. These two effects can be explained with the assumption that the PMS effect is due to an increase in the rate of internal conversion (kh), whereas the Mg2+ effect is due to a decrease in the rate of energy transfer (kt), between the two photosystems.4. From the relative ratio of φf with DCMU and DCMU plus Mg2+, we have calculated kt (the rate constant of energy transfer between Photosystems II and I to be 4.2·108 s?1, and φt (quantum yield of this transfer) to be 0.12. 相似文献