Abstract

In Synechocystis sp. PCC 6803 and some other cyanobacteria photosystem I reaction centres exist predominantly as trimers, with minor contribution of monomeric form, when cultivated at standard optimized conditions. In contrast, in plant chloroplasts photosystem I complex is exclusively monomeric. The functional significance of trimeric organization of cyanobacterial photosystem I remains not fully understood. In this study, we compared the photosynthetic characteristics of PSI in wild type and psaL knockout mutant. The results show that relative to photosystem I trimer in wild-type cells, photosystem I monomer in psaL⁻ mutant has a smaller P700⁺ pool size under low and moderate light, slower P700 oxidation upon dark-to-light transition, and slower P700⁺ reduction upon light-to-dark transition. The mutant also shows strongly diminished photosystem I donor side limitations [quantum yield Y(ND)] at low, moderate and high light, but enhanced photosystem I acceptor side limitations [quantum yield Y(NA)], especially at low light (22 µmol photons m⁻² s⁻¹). In line with these functional characteristics are the determined differences in the relative expression genes encoding of selected electron transporters. The psaL⁻ mutant showed significant (ca fivefold) upregulation of the photosystem I donor cytochrome c₆, and downregulation of photosystem I acceptors (ferredoxin, flavodoxin) and proteins of alternative electron flows originating in photosystem I acceptor side. Taken together, our results suggest that photosystem I trimerization in wild-type Synechocystis cells plays a role in the protection of photosystem I from photoinhibition via maintaining enhanced donor side electron transport limitations and minimal acceptor side electron transport limitations at various light intensities.

中文翻译：

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需要光系统I的三聚体组织来维持蓝藻集胞藻（Synechocystcystis sp。）中平衡的光合电子流。PCC 6803

摘要

在集胞藻中。在标准优化条件下培养时，PCC 6803和其他一些蓝细菌光系统I反应中心主要以三聚体形式存在，而单体形式的贡献很小。相反，在植物叶绿体光系统中，I复合物仅是单体。尚不完全了解蓝藻光系统I的三聚体组织的功能意义。在这项研究中，我们比较了野生型和psaL基因敲除突变体中PSI的光合特性。结果表明，相对于光系统I在野生型细胞中的三聚体，光系统I中单体PSAL ^-突变体具有更小的P700 ⁺在弱光和中度光照下的碳黑池大小，从暗到亮的过渡时P700的氧化速度较慢，从亮到暗的过渡时P700 ⁺还原的速度较慢。该突变体还显示出在弱光，中光和强光下，光系统I供体侧的局限性[量子产率Y（ND）]大大降低，但在弱光（22 µmol）下，尤其是在弱光下，增强了光系统I受主侧的局限性[量子产率Y（NA）]。光子m ^-2  s ^-1）。与这些功能特征一致的是编码所选电子转运蛋白的相对表达基因中确定的差异。所述PSAL ^-所述光系统I供体细胞色素的突变体显示显著（约五倍）上调Ç ₆，并下调光系统I受体（铁氧还蛋白，黄酮毒素）和源自光系统I受体侧的替代电子流的蛋白质。两者合计，我们的结果表明，野生型集胞藻细胞中的光系统I三聚化通过在各种光强度下维持增强的供体侧电子传输限制和最小的受体侧电子传输限制，在保护光系统I免受光抑制中起作用。