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首页> 外文会议>NATO Advanced Research Workshop on The Chloroplast: From Molecular Biology to Biotechnology Kolymbari-Chania, Crete, Greece 10-15 August 1998 >The effect of light on the biosynthesis and function of nadph-protochlorophyllide oxidoreductases (PORs) a and b in seedlings of arabidopsis thaliana and hordeum vulgare
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The effect of light on the biosynthesis and function of nadph-protochlorophyllide oxidoreductases (PORs) a and b in seedlings of arabidopsis thaliana and hordeum vulgare

机译：光对拟南芥和大麦种子幼苗中纳豆原绿叶素氧化还原酶（PORs）a和b的生物合成和功能的影响

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摘要

Most oxygenic photosynthetic organisms have two options to complete the synthesis of chlorophyll. In a light-independent reaction the immediate precursor of chlorophyllide, protochlorophyllide (Pchlide), can be reduced to chlorophyllide through a Pchlide- reducing enzyme that consists of three subunits Ch L, Ch B and Ch N that in plants are encoded by chloroplast DNA. In addition to this light-independent enzyme they also contain a nuclear DNA-encoded light-dependent NADPH-Pchlide oxidoreductase (POR) (Fig. 1). In angiosperms, however, only one of these two routes is active. Through the loss of the light-independent enzyme angiosperms are no longer able to use this reaction during the night to avoid the accumulation of Pchlide, a photosensitizing pigment, that upon illumination may lead to severe photooxidative damage (Fig. 1). In order to compensate for the lack of the light-independent Pchlide-reducing enzyme angiosperms seem to have evolved at least two protection mechanisms that minimize the risk of photooxidative damage durign the transition from the dark to the light. First, in contrast to other plants, some angiosperms - and also some of the gymnosperms - possess a second POR enzyme (2-6). It is tempting to speculate that angiosperms use this additional POR enzyme as part of a protection strategy against reactive oxygen species, that in particular during seedling development may lead to the rapid bleaching and death of etiolated seedings after they have been exposed to light. Second, a feed-back inhibitory loop has been described in higher plants through which further synthesis of #delta#-aminolevulinic acid, a precursor common to all porphyrins, will be stopped once a critical level of Pchlide has been reached in the dark.
机译：大多数含氧光合生物都有两种选择来完成叶绿素的合成。在不依赖光的反应中，叶绿素的直接前体原叶绿素（Pchlide）可以通过由植物中由叶绿体DNA编码的三个亚基Ch L，Ch B和Ch N组成的Pchlide还原酶还原为叶绿素。除了这种不依赖光的酶之外，它们还包含核DNA编码的依赖光的NADPH-Pchlide氧化还原酶（POR）（图1）。但是，在被子植物中，只有这两种途径之一有效。由于失去了与光无关的酶，被子植物不再能够在夜间利用该反应来避免光敏性色素Pchlide的积累，这种物质在光照下会导致严重的光氧化损伤（图1）。为了补偿缺乏光依赖性的降低Pchlide的酶，被子植物似乎已经进化出至少两种保护机制，以最小化从黑暗到光亮过渡期间光氧化损伤的风险。首先，与其他植物相反，一些被子植物-以及一些裸子植物-具有第二种POR酶（2-6）。试图推测被子植物使用这种附加的POR酶作为针对活性氧的保护策略的一部分，特别是在幼苗发育期间，暴露于光下的黄化种子可能会迅速脱色并死亡。其次，已经在高等植物中描述了反馈抑制环，通过该环，一旦在黑暗中达到临界水平的氯化物，将停止进一步合成所有卟啉通用的前体δ-氨基乙酰丙酸。

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