Abstract

Imbalanced light absorption by photosystem I (PSI) and photosystem II (PSII) in oxygenic phototrophs leads to changes in interaction of photosystems altering the linear electron flow. In plants and green algae, this imbalance is mitigated by a partial migration of the chlorophyll a/b containing light-harvesting antenna between the two photosystem core complexes. This migration is registered as fluorescence changes of the pigment apparatus and is termed the reverse transitions between States 1 and 2. By contrast, the molecular mechanism of State 1/2 transitions in phycobilisome (PBS)-containing photosynthetics, cyanobacteria and red algae, is still insufficiently understood. The suggested hypotheses – PBS movement along the surface of thylakoid membrane between PSI and PSII complexes, reversible PBS detachment from the dimeric PSII complex, and spillover – have some limitations as they do not fully explain the accumulated data. Here, we have recorded changes in the stationary fluorescence emission spectra of red algae and cyanobacteria in States 1/2 at room temperature, which allowed us to offer an explanation of the existing contradictions. The change of room temperature fluorescence of chlorophyll belonged to PSII was revealed, while the fluorescence of PBS associated with the PSII complexes remained during States 1/2 transitions at the stable level. Only the reversible dissociation of PBS from the monomeric PSI was revealed earlier which implied different degree of surface contact of PBS with the two photosystems. The detachment of PBS from the PSI corresponds to ferredoxin oxidation as electron carrier and the increase of cyclic electron transport in the pigment apparatus in State I.

中文翻译：

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红色微藻和蓝藻光合装置中的状态1和状态2

摘要

光系统 I (PSI) 和光系统 II (PSII) 在含氧光养生物中的不平衡光吸收导致光系统相互作用的变化，从而改变线性电子流。在植物和绿藻中，这种不平衡通过叶绿素a/b的部分迁移而得到缓解在两个光系统核心复合体之间包含集光天线。这种迁移被记录为色素装置的荧光变化，被称为状态 1 和状态 2 之间的反向转换。相比之下，含有藻胆体 (PBS) 的光合作用、蓝细菌和红藻中状态 1/2 转换的分子机制是还是不够了解。所提出的假设——PBS 在 PSI 和 PSII 复合物之间沿类囊体膜表面移动、PBS 从二聚体 PSII 复合物分离以及溢出——有一些局限性，因为它们不能完全解释累积的数据。在这里，我们记录了室温下 1/2 州红藻和蓝藻的固定荧光发射光谱的变化，这使我们能够对现有的矛盾做出解释。揭示了属于PSII的叶绿素室温荧光的变化，而与PSII配合物相关的PBS的荧光在状态1/2跃迁期间保持在稳定水平。只有 PBS 与单体 PSI 的可逆解离较早被揭示，这意味着 PBS 与两个光系统的表面接触程度不同。PBS 与 PSI 的分离对应于作为电子载体的铁氧还蛋白氧化和状态 I 中色素装置中循环电子传输的增加。只有 PBS 与单体 PSI 的可逆解离较早被揭示，这意味着 PBS 与两个光系统的表面接触程度不同。PBS 与 PSI 的分离对应于作为电子载体的铁氧还蛋白氧化和状态 I 中色素装置中循环电子传输的增加。只有 PBS 与单体 PSI 的可逆解离较早被揭示，这意味着 PBS 与两个光系统的表面接触程度不同。PBS 与 PSI 的分离对应于作为电子载体的铁氧还蛋白氧化和状态 I 中色素装置中循环电子传输的增加。