Regulation of photosystem formation : A flexibility of energy-conversion system in thylakoids responding to environments

本研究旨在明确蓝藻光合作用中PSI/PSII的变化特征。从三个方面进行了表征。首先分析了PSI形成调控的分子机制。大部分工作都集中在PSI地层中目标台阶的识别上。载脂蛋白合成步骤分析表明，调控发生在翻译水平；平移在PSI光下被抑制，在PSII光下被释放。发现该调控与Chl - a生物合成有关。我们怀疑PSI的形成在chl a安装到载子蛋白的步骤(5)中受到调节。在第二个方面的研究中，我们研究了除蓝藻外的藻类生物的PSI/PSII变化。我们用红藻紫菜卟啉和绿藻莱茵衣藻进行了检验。结果表明，这些生物中PSI/PSII的变化方式与蓝藻相似。PSI/PSII在不同门中的变化表明，这种类型的调节机制是绿色植物的一种共同的氧合光合能力。我们在第三方面的研究是比较了色光诱导的PSI/PSII变化与环境胁迫诱导的非光态变化。CO_2-和Na^+-应力引起的ETS偏置状态类似于光从PSI光移到PSII光引起的偏置状态。正如预期的那样，这两种环境压力导致PSI/PSII比增加，就像光移一样。结果清楚地表明，PSI/PSII比率受到ETS状态的调节，支持了我们之前的假设。

The study aimed to make clear the characteristics of PSI/PSII variation found with photosynthesis of cyanophytes. The characterization was made in three aspects. The first was analysis of molecular mechanism for requlation of PSI formation. Most effort was paid focusing on identification of the target step (s) in PSI formation. Analysis of steps for apoprotein synthesis revealed that the regulation occurs at translation level ; the translation is suppressed under PSI light and is released from suppression under PSII light. The regulation was found to correlate with Chl a biosynthesis. We suspect that PSI formation is regulated at the step (s) for chl a installation into apoprotein.In the study of the second aspect, we examined PSI/PSII variation with algal organisms other than cyanophytes. We examined with the red alga Porphyra yezoensis and the green alga Chlamydomonas reinhardtii. Results indicated that PSI/PSII variation occurs in these organisms in a similar manner to that in cyanophytes. PSI/PSII variation in different phyla indicates that the regulatory mechanism of this type is a common ability of oxygenic photosynthesis of green plants.Our study for the third aspect was made for comparison of PSI/PSII variation induced by chromatic light with the variation induced by environmental stresses other than light regime. CO_2- and Na^+-stresses cause a biassed state of ETS as similar to that caused by light shift from PSI light to PSII light. As expected, the two environmental stresses caused an increase in PSI/PSII ratio, like the light shift. Results clearly indicate that PSI/PSII ratio is regulated in response to the state of ETS and support our previous hypothesis.