共查询到20条相似文献,搜索用时 15 毫秒
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Gantt E 《Photosynthesis research》2011,107(1):1-6
The integrated functioning of two photosystems (I and II) whether in cyanobacteria or in chloroplasts is the outstanding sign
of a common ancestral origin. Many variations on the basic theme are currently evident in oxygenic photosynthetic organisms
whether they are prokaryotes, unicellular, or multicellular. By conservative estimates, oxygenic photosynthesis has been around
for at least ca. 2.2–2.7 billions years, consistent with cyanobacteria-type microfossils, biomarkers, and an atmospheric rise
in oxygen to less than 1.0% of the present concentration. The presumptions of chloroplast formation by the cyanobacterial
uptake into a eukaryote prior to 1.6 BYa ago are confounded by assumptions of host type(s) and potential tolerance of oxygen
toxicity. The attempted dating and interrelationships of particular chloroplasts in various plant or animal lineages has relied
heavily on phylogenomic analysis and evaluations that have been difficult to confirm separately. Many variations occur in
algal groups, involving the type and number of accessory pigments, and the number(s) of membranes (2–4) enclosing a chloroplast,
which can both help and complicate inferences made about early or late origins of chloroplasts. Integration of updated phylogenomics
with physiological and cytological observations remains a special challenge, but could lead to more accurate assumptions of
initial and extant endosymbiotic event(s) leading toward stable chloroplast associations. 相似文献
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Spinach chloroplasts exposed to iodide can be washed free of the bulk of the iodide. In the presence of lactoperoxidase and H2O2, iodide can be introduced into chloroplasts in high amounts and in non diffusible forms. The resultant particles, which have been named iodochloroplasts, extrude their iodide upon stimulation by light. The form and the amount of extruded iodide bears a definite relationship to the amount of incident light. A flash of marginally effective light is additive to the next such flash even after a lapse of 10 min of darkness. These and other properties of iodochloroplasts may make them of great use in the study of intermediate reactions of photosynthesis. 相似文献
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Dielectrophoresis is the migration of neutral particles in a nonuniform electric field (a.c. or d.c.) toward the region of highest field intensity. Dielectrophoresis should be distinguished from electrophoresis which is the migration of charged particles in electric fields. Chloroplasts, isolated from spinach leaves, can be collected on platinum electrodes by dielectrophoresis. Stripped chloroplasts lacking outer envelopes and stroma were prepared from fresh spinach leaves in a 0.5 M sucrose-0.05 M Tris buffer (pH 7.4). The chloroplast preparation was desalted with a mixed anion-cation resin to a resistivity of 3 · 104–5 · 104 ohm · cm. Dielectrophoresis was conducted in a pin-pin type leucite cell 3.2 mm in diameter and 1.5 mm deep. The 0.425-mm diameter electrodes were 0.85 mm apart and 0.05 mm below the surface of the cell. The collection of chloroplasts with ac current is a function of the frequency. 3-(3,4-Dichlorophenyl)-1,1-dimethylurea (DCMU)-stabilized chloroplasts had collection maxima at 300, 1 · 106, and 3 · 107 Hz when run at 50 V. The rate of collection is a function of the square root of the time. Both DCMU and darkness tend to stabilize collections. It is suggested that dielectrophoresis may be a useful tool for the study of chloroplast physiology and perhaps, for the preparation and purification of chloroplasts. 相似文献
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Dielectrophoresis of chloroplasts 总被引:1,自引:0,他引:1
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Delayed fluorescence and the high-energy state of chloroplasts 总被引:9,自引:0,他引:9
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Isolation and properties of the envelope of spinach chloroplasts 总被引:48,自引:0,他引:48
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Lysolecithin was added to spinach chloroplasts in suspension,and its effect as a detergent on structure and electron transportactivities was examined. At low concentrations of lysolecithin,the activities of FeCN photoreduction and O2-linked DCPIPH2photo-oxidation were stimulated but the photoreduction of NADPwas not enhanced and decreased with an increase in concentration.Absorption bands over the whole visible region were intensifiedwithout any shifts. At high concentrations, the activities ofFeCN photoreduction and O2-linked DCPIPH2 photo-oxidation decreasedfrom a maximum to 1050% of the control activity, andNADP photoreduction was completely inhibited. Absorption bandswere further intensified and the red band was slightly shifted.Results indicate that lysolecithin treatment is useful in chloroplastbiochemistry. Lysolecithin formation and the deterioration ofchloroplasts during light-aging is also discussed. (Received August 15, 1974; ) 相似文献
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BN Ivanov 《Biochemistry. Biokhimii?a》1998,63(2):133-138
Current views concerning the generation of superoxide radicals and hydrogen peroxide in chloroplasts as well as their toxic influences on photosynthesis are presented. Systems of H2O2 detoxification including the ascorbate peroxidase reactions and the ascorbate regenerating reactions are described. Data concerning mechanisms of monodehydroascorbate reduction by the photosynthetic electron transport chain are reviewed. The participation of the Mehler-peroxidase reaction in building of a proton gradient across the thylakoid membrane and its possible input in ATP synthesis and in protection from photoinhibition are analyzed. Ascorbate functions in chloroplasts and the need to consider the high concentration of ascorbate in chloroplasts when photosynthetic reactions in vivo are discussed are briefly reviewed. 相似文献
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Three endopeptidases (EP2, EP3, and EP4) were identified after fractionation of pea (Pisum sativum, var Feltham First) chloroplast stromal extracts. All three were identified by their ability to cleave in vitro-synthesized preplastocyanin to lower molecular weight forms. EP2 is inhibited by phenylmethylsulfonylfluoride, and both EP2 and EP3 are inhibited by the heavy metal chelators 1,10-phenanthroline and EDTA. A further endopeptidase, EP5, was identified in Triton X-100 extracts of thylakoid membranes. Experiments involving contrifugation through a sucrose pad indicate that EP5 either has a high molecular weight or is associated with a thylakoid protein complex. EP5 is effectively inhibited by phenylmethylsulfonylfluoride, iodoacetate, and 1,10-phenanthroline, but not by EGTA. The implications of these results for the analysis of chloroplast protein maturation are discussed, and an improved protocol for the purification of the stromal processing peptidase is described which ensures the removal of EP2, the most active of the stromal peptidases analysed in this study. 相似文献
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Spinach class II chloroplasts were treated with snake venom phospholipase A2 in the presence of bovine serum albumin, and separated by sucrose-density centrifugation. The treatment yielded phospholipid-depleted chloroplasts which had lost 82.6% of the original phospholipids. About 20% of the phospholipids of chloroplasts were resistant to enzyme attack. These results suggest that phospholipids exist in two states in chloroplast membranes. In spite of considerable phospholipid depletion, the chloroplast preparations retained a large portion of their photoactivities, i.e. light-induced electron transport, light-induced H+ uptake, and light-induced shrinkage. However, cyclic photophosphorylation was significantly affected with the phospholipid removal. 相似文献
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The ultrastructure of chloroplasts 总被引:1,自引:0,他引:1
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Translation in chloroplasts 总被引:18,自引:0,他引:18
Zerges W 《Biochimie》2000,82(6-7):583-601
The discovery that chloroplasts have semi-autonomous genetic systems has led to many insights into the biogenesis of these organelles and their evolution from free-living photosynthetic bacteria. Recent developments of our understanding of the molecular mechanisms of translation in chloroplasts suggest selective pressures that have maintained the 100-200 genes of the ancestral endosymbiont in chloroplast genomes. The ability to introduce modified genes into chloroplast genomes by homologous recombination and the recent development of an in vitro chloroplast translation system have been exploited for analyses of the cis-acting requirements for chloroplast translation. Trans-acting translational factors have been identified by genetic and biochemical approaches. Several studies have suggested that chloroplast mRNAs are translated in association with membranes. 相似文献