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101.
102.
103.
Photosystem I-dependent cyclic electron transport is shown to operate in intact spinach chloroplasts with oxaloacetate, but not with nitrite or methylviologen as electron acceptors. It is regulated by the redox state of the chloroplast NADP system. Inhibition of cyclic electron transport by antimycin A occurs immediately on addition of this antibiotic in the light. It is unrelated to a different function of antimycin A, inhibition of nonphotochemical quenching of chlorophyll fluorescence, which requires prior dissipation of the transthylakoid proton gradient before antimycin A can become effective. 相似文献
104.
Abstract: Seasonal changes in the efficiency of charge separation in PSII were studied in Thuja occidentalis (L.) and Chamaecyparis lawsonia (A. Murray bis.). Maximum light-dependent charge separation decreased with decreasing temperatures in early winter in both species, but this was less drastic in Chamaecyparis than in Thuja. No positive relationship was seen between photoinhibition and irradiance. Rather, photoinhibition increased as photon flux densities decreased towards midwinter, and it decreased as photon flux densities increased towards spring. However, the decrease in maximum light-dependent charge separation was much stronger on the light-exposed upper surface of the twigs, where in Thuja visible browning occurred, than on the underside of the twigs. During spring, recovery of the photosynthetic efficiency and regreening were observed as both mean temperatures and irradiance increased. Transfer in midwinter of strongly photo-inhibited twigs of Thuja to temperatures close to 20 °C resulted in considerable recovery of PSII activity within several days when low light was also present. Recovery did not occur at temperatures close to freezing or at room temperature in darkness. An analysis of fluorescence quenching suggested photoprotective dissipation of excess radiation not only in the light harvesting antennae of PSII but also in the reaction centres. Reaction centre quenching appeared to be stronger in Thuja than in Chamaecyparis. PSI was fully active in twigs whether or not PSII was photoinhibited. The antioxidant ascorbate was almost fully reduced even in midwinter. 相似文献
105.
106.
Carbon assimilation of spinach (Spinacia oleracea L.) leaves was measured in the presence of 2000l· l–1CO2 and 2% O2 in the gas phase to suppress photorespiratory reactions and to reduce stomatal diffusion resistance. Simultaneously, membrane parameters such as modulated chlorophyll fluorescence, oxidation of P700 in the reaction centre of photosystem I, and apparent changes in absorbance at 535 nm were recorded. After light-regulated enzymes were activated at a high irradiance, illumination was changed. About 3 min later (to maintain the previous activation state of enzymes), leaves were shock-frozen and freeze-dried. Chloroplasts were isolated nonaqueously and analysed for ATP, ADP, inorganic phosphate, NADPH and NADP. Observations made under the chosen conditions differed in some important aspects from those commonly observed when leaves are illuminated in air. (i) Not only assimilation, but also the phosphorylation potential [ATP]/([ADP]·[Pi]) increased hyperbolically with irradiance towards saturation. In contrast, the ratio of NADPH to NADP did not change much as irradiances increased from low to high photon flux densities. When ATP, the phosphorylation potential and the assimilatory force, FA (the product of phosphorylation potential and NADPH/NADP ratio), were plotted against assimilation, ATP increased relatively less than assimilation, whereas the phosphorylation potential increased somewhat more steeply than assimilation did. A linear relationship existed between assimilation and FA at lower irradiances. The assimilatory force FA increased more than assimilation did when irradiances were very high. Differences from previous observations, where FA was under some conditions higher at low than at high rates of carbon assimilation, are explained by differences in flux resistances caused not only by stomatal diffusion resistance but also by differences in the activity of light-regulated enzymes, (ii) The relationship between P700 oxidation and a fast absorption change with a maximum close to 520 nm on one hand and carbon assimilation on the other hand was largely linear under the specific conditions of the experiments. A similar linear relationship existed also between the quantum efficiency of electron flow through photosystem II and the quantum efficiency of photosystem I electron transport. (iii) Whereas the increase in non-photochemical fluorescence quenching, qN, was similar to the increase in assimilation, the relationship between light scattering and assimilation was distinctly sigmoidal. Light scattering appeared to be a better indicator of control of photosystem II activity under excessive irradiation than qN. (iv) The results are discussed in relation to the relative significance of chloroplast levels of ATP and NADPH and of the assimilatory force FA in driving carbon assimilation. From the observations, the proton/electron (H+/e–) ratio of linear electron transport is suggested to be 3 and the H+/ATP ratio to be 4 in leaves. An H+/e– ratio of 3 implies the existence of an obligatory Q-cycle in leaves.Abbreviations FA
assimilatory force
- Fo
fluorescence after long dark adaptation
- Fm
maximum fluorescence level
- Fs
steady-state fluorescence
- PGA
3-phosphoglycerate
- PFD
photon flux density
- P700 (P700+)
electron-donor pigment in the reaction center of PSI (its oxidized form)
- QA
primary quinone acceptor of PSII
- qP
photochemical quenching
- qN
non-photochemical quenching
- PSII
relative quantum efficiency of energy conversation at the level of photosystem II
- PSI
relative quantum efficiency of photosystem II
This research was supported by the Sonderforschungsbereich 251 of the University of Würzburg and the Stiftung Volkswagenwerk. U.G. is a member of the Graduate College of the Julius-von-Sachs Institut für Biowissenschaften, University of Würzburg, being on leave from Tartu University, Tartu, Estonia. The authors are grateful to Prof. A. Laisk, Chair of Plant Physiology, Tartu University, for stimulating discussions. 相似文献
107.
A parsimony analysis was performed on restriction sites at the Hba-ps4
pseudogene locus within one of four inversions associated with mouse t
haplotypes. The results suggest that all t haplotypes form a monophyletic
group and that the in (17)4 inversion originated before the radiation of
the Mus musculus species complex but after the divergence of the lineages
leading to M. spretus, M. abbotti, and M. hortulanus. A time frame based on
the evolutionary rate of mouse pseudogenes places the origin of this t
haplotype inversion at 1.5 Mya, or approximately 1.5 Myr after the origin
of the more proximal t complex inversion, in (17)2. The accumulated
evidence indicates that complete t haplotypes have been assembled in a
stepwise manner, with each of these inversions occurring on separate
chromosomal lineages and at different evolutionary times. In addition, the
evolutionary relationships of pseudogene sequences resulting from genetic
exchange between wild-type and t haplotype alleles were examined. Analysis
of sequences from the 5' and 3' sides of a putative site of recombination
resulted in cladograms with different topologies. The implications for
hypotheses concerning the evolutionary forces acting on t haplotypes and
their rapid propagation throughout worldwide populations of mice are
discussed.
相似文献
108.
109.
Intact spinach chloroplasts, capable of high rates of photochemical oxygen evolution with CO2 as electron acceptor (120-350 mumol O2 mg chlorophyll-1 h-1) were examined for cytochrome redox changes. The response of the cytochromes in intact chloroplasts to oxidants and reductants appears to be governed by the permeability of the chloroplast envelope. The low potential cytochromes (b-559LP and b-563) were more slowly reduced at 25 degrees C by dithionite than is the case with broken chloroplasts. At 0 degrees C, the reduction of the low potential cytochromes in intactchloroplasts was extremely slow. The chloroplast envelope is impermeable to ferricyanide, slowly permeable to ascorbate and rapidly permeable to reduced dichlorophenolindophenol. Light-induced redox changes of cytochrome b-563 in intact chloroplasts were examined both at 0 degrees and 25 degrees C. A red/far-red antagonism on the redox changes of cytochrome b-563 was observed at 0 degrees C under anaerobic conditions. 3-(3,4-dichlorophenyl)-1, 1-dimethlyurea (DCMU) inhibited the photoreduction of cytochrome b-563 in red light following far-red illumination. The photooxidation of cytochrome b-563 under anaerobic conditions was not influenced by DCMU or 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB). The photoreduction of cytochrome b-563 under aerobic conditions was much less efficient than its photooxidation under anaerobic conditions. Developing pea chloroplasts showed much greater light-induced redox changes of cytochrome b-563 than did intact spinach chloroplasts. Our data are consistent with the view that cytochrome b-563 functions on a cyclic pathway around Photosystem I, but it appears that cyclic flow is sensitive to the relative poising of the redox levels of cytochrome b-563 and the components of the non-cylic pathway. 相似文献
110.
Oscillations of photosynthesis induced in leaves of Vicia faba L. were accompanied by oscillations not only in the pH of the chloroplast stroma, but also by pH oscillations in the cytosol and in the vacuole of leaf mesophyll cells. Cytosolic pH oscillations were in phase with stromal oscillations, but antiparallel to vacuolar pH oscillations. During maxima of photosynthesis, the cytosolic pH exhibited maxima and the vacuolar pH minima. Vacuolar acidification is interpreted to be the result of energized proton transport from the cytosol into the vacuole. Since the ratio of dihydroxyacetone phosphate to phosphoglycerate is maximal during the peaks of photosynthesis (Stitt et al., 1988, J. Plant Physiol. 133, 133–143; Laisk et al., 1991, Planta 185, 554–562), while the activity of NADP-malic dehydrogenase is highest during minima of photosynthesis (Scheibe and Stitt, 1988, Plant Physiol. Biochem. 26, 473–481), the present data indicate in agreement with earlier observations (Yin et al., 1991, Planta 184, 30–34) that light-dependent cytosolic energization is brought about by the oxidation of dihydroxyacetone phosphate rather than of malate. They also indicate that the over-reduction of the electrontransport chain observed during minima of photosynthesis is relieved not predominantly by oxaloacetate reduction and export of the resulting malate from the chloroplasts but by another reaction, presumably oxygen reduction.Abbreviations CDCF
5-(and 6-)carboxy-2,7-dichlorofluorescein 相似文献