光合放氧系统的结构和放氧过程

对自然界从厌氧细菌的光合作用到放氧植物的光合作用作一简单介绍,并着重阐明光合放氧系统的结构和放氧的过程,以及锰、氯、钙与氧释放的关系。     

巨大螺旋藻PSII颗粒光合放氧与多肽组成关系的研究

由常温下培养的巨大螺旋藻制备的细胞、类囊体膜片层、ＰＳⅡ颗粒均具一定的放氧活性,且随着制备物的纯化,放氧活性逐渐提高。二价阳离子Ｃａ＾２＋对于维持光合膜放氧活性是必需的;ＰＳⅡ颗粒放氧复合物包含１２条多肽,较高等植物多肽组分复杂;类囊体膜多肽分则极为复杂;盐洗和多肽重组实验表明５５,５０,２６ｋＤ多肽与外在放氧蛋白组成及功能有关,特别是５５,２６ｋＤ多肽是放氧不可缺少的组分。     

羟胺和肼对烟草光合放氧影响的差异

羟胺对Ｓ状态系统的还原作用比强,它可将水裂解的Ｓ状态系统从Ｓ０还原到Ｓ－２,肼只能将Ｓ０还原到Ｓ－１。肼对光合水裂解的抑制作用较羟胺强,在高浓度下（１０００μｍｏｌ／Ｌ）它可完全抑制光合水裂解,使烟草叶绿体产生强烈的氧吸收,羟胺可使暗适应叶绿体的Ｓ状态系统的Ｓｉ（ｉ＝１～４）分布趋向稳态,高浓度羟胺（１０００μｍｏｌ／Ｌ）仍不能完全抑制氧释放,并且对叶绿体氧吸收的诱导作用也很小。     

光合放氧的电极电位测定法的研究

介绍了用电极电位法测定植物的光合放氧速率,由此可以测定其放氧活性,此法具有应用面广、设备简便、灵敏度高、反应快及可以连续记录的特点,是一种研究光合作用的新方法。     

放氧复合物蛋白质组分的研究进展

绿色植物利用太阳能氧化水产生分子氧(光合裂解水)的反应是光合作用的一个基本过程.水经过此反应释出的氧气是地球上维持需氧生命的唯一氧气来源,释出的电子、质子为光合作用中后面步骤的进行所必需.人们对这个重要过程的认识需追溯到二百年前J.Priestley 和Ingen-Housz 的开拓性的工作.那时氧气尚未发现,Priestley 观察到植物有改善空气的功能,Ingen-Housz 并进一     

水分胁迫对甘薯叶肉细胞光合电子传递的影响

水分胁迫降低了甘薯叶肉细胞的光合能力。在有解偶联剂存在时,水分胁迫对叶肉细胞的光合电子传递没有影响,但在无解偶联剂存在下,水分胁迫促进了甘薯叶肉细胞的光合电子传递,表现出明显的解偶联效应。水分胁迫伤害了甘薯叶绿体偶联因子结构,使ATP合成受阻,叶肉细胞的光合滞后期加长。     

光照、温度和pH对雨生红球藻光合特性的影响

采用测定光合放氧速率和荧光动力学的方法,研究分析了光照强度、温度和pH对雨生红球藻Haematococcus pluvialis CG-11绿色游动细胞阶段光合作用特性的影响。结果表明,H. pluvialis CG-11光合作用的饱和光强为109.1 μmol/m2·s,最大光合放氧速率为75.9 μmol O2/mg Chla·h;适宜的生长温度范围在25－30℃之间,温度在25℃时光合速率最大;pH在7.5－8.0范围内,光合效率较高,在pH为7.5时放氧速率最大,为75.5 μmol O2/mg Chla·h。在实验pH条件下,H. pluvialis CG-11叶绿素荧光动力学参数呈现出相似的趋势,在6.0－7.5范围内,Fv/ Fm、Fv/ F0、ΦPSⅡ和ETR值随pH升高而增大,pH为7.5时达到最大值,pH超过7.5时,Fv/ Fm和Fv/ F0值明显下降,而ΦPSⅡ和ETR的下降趋势不明显。     

水分胁迫对甘薯叶肉细胞光合电子传递的影响

水分胁迫降低了甘薯叶肉细胞的光合能力。在有解偶联剂存在时,水分胁迫对叶肉细胞的光合电子传递没有影响,但在无解偶联剂存在下,水分胁迫促进了甘薯叶肉细胞的光合电子传递,表现出明显的解偶联效应。水分胁迫伤害了甘薯叶绿体偶联因子结构,使ＡＴＰ合成受阻,叶肉细胞的光合滞后期加长。     

Photosynthesis ofChlorella vulgaris as affected by diaqua(4-chloro-2-methylphenoxyacetato)copper(II) complex

Inhibitory effect of diaqua(4-chloro-2-methylphenoxyacetato)copper(II) complex (MCPACu) on oxygen evolution rate in algaeChlorella vulgaris was found. Electron paramagnetic resonance and fluorescence spectroscopy showed that the sites of action of MCPACu are Z⁺ and Y⁺ intermediates on the donor side of photosystem 2 as well as the manganese cluster in the oxygen evolving complex.     

An in situ study of photosynthetic oxygen exchange and electron transport rate in the marine macroalga Ulva lactuca (Chlorophyta)

Direct comparisons between photosynthetic O₂ evolution rate and electron transport rate (ETR) were made in situ over 24 h using the benthic macroalga Ulva lactuca (Chlorophyta), growing and measured at a depth of 1.8 m, where the midday irradiance rose to 400–600 μmol photons m⁻² s⁻¹. O₂ exchange was measured with a 5-chamber data-logging apparatus and ETR with a submersible pulse amplitude modulated (PAM) fluorometer (Diving-PAM). Steady-state quantum yield ((F_m′−F_t)/F_m′) decreased from 0.7 during the morning to 0.45 at midday, followed by some recovery in the late afternoon. At low to medium irradiances (0–300 μmol photons m⁻² s⁻¹), there was a significant correlation between O₂ evolution and ETR, but at higher irradiances, ETR continued to increase steadily, while O₂ evolution tended towards an asymptote. However at high irradiance levels (600–1200 μmol photons m⁻² s⁻¹) ETR was significantly lowered. Two methods of measuring ETR, based on either diel ambient light levels and fluorescence yields or rapid light curves, gave similar results at low to moderate irradiance levels. Nutrient enrichment (increases in [NO₃ ⁻], [NH₄ ⁺] and [HPO₄ ^2-] of 5- to 15-fold over ambient concentrations) resulted in an increase, within hours, in photosynthetic rates measured by both ETR and O₂ evolution techniques. At low irradiances, approximately 6.5 to 8.2 electrons passed through PS II during the evolution of one molecule of O₂, i.e., up to twice the theoretical minimum number of four. However, in nutrient-enriched treatments this ratio dropped to 5.1. The results indicate that PAM fluorescence can be used as a good indication of the photosynthetic rate only at low to medium irradiances. This revised version was published online in June 2006 with corrections to the Cover Date.     

Efficient separation of subfossil Chironomidae from lake sediments

Electron transport system (ETS) activity, CO₂ evolution, O₂ consumption, N₂-fixation (C₂H₂ reduction) and methanogenesis were appropriately measured in aerobic and anaerobically incubated sediment at 4, 10 and 20 ° C to better characterize these activities under different incubation conditions. ETS activity was always higher in the aerobically incubated sediment at all three incubation temperatures, whereas (C₂H₂ reduction was always greater in the anaerobic sediment. Carbon dioxide evolution was detected only in the aerobic sediment at 10 and 20 ° C but not at 4 ° C. Methane evolution in anaerobic sediment increased gradually with an increase in the incubation temperature.     

Oxygen supply to immobilized cells: 1. Oxygen production by immobilized Chlorella pyrenoidosa

Oxygen supply at high cell densities of aerobic organisms is a great problem in immobilized cell preparations. To investigate the possibility of in situ oxygen generation the alga Chlorella pyrenoidosa was immobilized on alginate beads. The conditions for optimal oxygen production were investigated and in long term experiments the preparations were successful for at least 30 days.     

Besonderheiten bei der Ermittlung der Primärproduktion in der Elbe aus Sauerstoff-Ganglinien. Some Particularities in Estimating Primary Productivity in the River Elbe Using Oxygen Time Curves

The phytoplanktonic primary production was estimated in the River Elbe (average flow 325 m³/s) by ODUM 's twin and single curve analysis of changes in the oxygen content (1- and 2- SGA). The results were affected by the severe and varying waste water load and the non-uniform conditions along the upstream river stretch. It is shown how the gross primary productivity was corrected by using the photosynthesis-light-relationship. At favourable measuring sites, single curve analysis gives similar values as ODUM 's twin curve method. But they scatter more when applied to establish the photsynthesis-light-relationship.     

Inhibition of chlororespiration by myxothiazol and antimycin A in Chlamydomonas reinhardtii

Myxothiazol and antimycin A are shown to suppress the oxygen transient previously attributed to the flash-induced inhibition of chlororespiration in Chlamydomonas reinhardtii (Peltier et al. 1987, Biochim Biophys Acta 893: 83–90). However, these two compounds do not affect the photosynthetic electron transport chain as inferred by the insensitivity of the CO₂-dependent photosynthetic O₂ evolution and of the flash-induced electrochromic effect. Chlorophyll fluorescence induction measurements carried out in dark-adapted cells of a mutant of Chlamydomonas lacking photosystem 1, show that myxothiazol and antimycin A significantly increase the redox state of the photosystem 2 acceptors. We conclude from these results that chlororespiration is inhibited by myxothiazol and antimycin A and that the site of inhibition is located on the dark oxidation pathway of the plastoquinone pool. This inhibition is interpreted through the involvement of a myxothiazol and antimycin A sensitive cytochrome in the chlororespiratory chain.Abbreviations cyt cytochrome - PQ plastoquinone - PS photosystem     

Plastoquinone as a common link between photosynthesis and respiration in a blue-green alga

The role of plastoquinone in a thermophilic blue-green alga, Shynechococcus sp., was studied by measuring reduction kinetics of cytochrome 553 which was oxidized with red flash preferentially exciting photosystem I. Sensitivity of the cytochrome reduction to DBMIB indicates that cytochrome 553 accepts electrons from reduced plastoquinone. Plastoquinone is in turn reduced in cells without electrons from photosystem II, since DCMU, which inhibited methyl viologen photoreduction more strongly than DBMIB, failed to affect the cytochrome reduction. Participation of cyclic electron transport around photosystem I in cytochrome reduction in the presence of DCMU was excluded, because methyl viologen and antimycin A had no effect on the cytochrome kinetics. On the other hand, electron donation from endogenous substrates to plastoquinone was suggested from decreases in rate of the cytochrome reduction by dark starvation of cells and also from restoration of fast reduction kinetics by the addition of exogenous substrates to or by reillumination of starved cells.KCN, which completely suppressed respiratory O₂-uptake, induced a marked acceleration of the cytochrome reduction in starved cells. The poison was less or not effective in stimulating the cytochrome reduction in more extensively starved or reilluminated cells.Results indicate that plastoquinone is functioning not only in the photosynthetic but also in the respiratory electron transport chain, thereby forming a common link between the two energy conservation systems of the blue-green alga.

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