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

本研究旨在弄清蓝藻光合作用过程中PSI/PSII的变化特征。从三个方面对其进行了刻画。一是PSI形成调控的分子机制分析。大部分精力都集中在确定PSI形成的目标步骤(S)上。对载脂蛋白合成步骤的分析表明，这种调节发生在翻译水平；翻译在PSI光下受到抑制，在PSII光下从抑制中释放出来。这一调节被发现与Chl a的生物合成有关。在第二个方面的研究中，我们研究了藻类生物而不是蓝藻的PSI/PSII的变化。我们对红藻条斑紫菜和绿藻莱茵衣藻进行了检测。结果表明，PSI/PSII变异在这些生物中发生的方式与蓝藻相似。PSI/PSII在不同门类的变化表明，这种类型的调节机制是绿色植物共同的氧合光合作用能力。第三个方面的研究比较了色光诱导的PSI/PSII变化与环境胁迫而不是光制度诱导的变化。CO_2~(2-)和Na~(++)胁迫引起ETS的偏置状态，类似于光从PSI光到PSII光的转换。正如预期的那样，这两种环境胁迫导致了PSI/PSII比率的增加，如光移。结果清楚地表明，PSI/PSII比率受ETS状态的调节，并支持我们之前的假说。

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.