Involvement of phycobilisome diffusion in energy quenching in cyanobacteria
Involvement of phycobilisome diffusion in energy quenching in cyanobacteria
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DOI：
10.1104/pp.105.061168
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发表时间：
2005-07-01
期刊：
影响因子：
7.4
通讯作者：
Mullineaux, CW
中科院分区：
文献类型：
--
作者：
Joshua, S;Bailey, S;Mullineaux, CW
激发能的非光化学猝灭（NPQ）是绿色植物中一种公认的现象，它可以保护光合作用装置在过度光照下免受光损伤。 NPQ 的诱导涉及光捕获装置功能的变化，形成将激发能转化为热量的猝灭中心。最近，在缺铁条件下生长的蓝细菌中也证实了类似的现象。在这些条件下，合成了额外的完整膜叶绿素蛋白 IsiA，因此 IsiA 可能是蓝藻中 NPQ 所必需的。我们之前使用光漂白后的荧光恢复来表明藻胆体在膜表面快速扩散，但当细胞浸入高渗透强度缓冲液中时被固定，显然是因为藻胆体和反应中心之间的相互作用稳定了。在这里，我们表明，当蓝藻集胞藻属的细胞。将经过长时间缺铁的PCC 6803浸入1M磷酸盐缓冲液中，仍然可以通过高光正常诱导NPQ。然而，猝灭状态的形成在这些条件下是不可逆的，这表明它涉及游离藻胆体与完整膜复合物的偶联，这是一种由 1 M 磷酸盐稳定的相互作用。荧光光谱与这个想法是一致的。光漂白测量后的荧光恢复证实，在 1 M 磷酸盐存在下，NPQ 的诱导伴随着藻胆体的固定。作为一个工作假设，我们提出在缺铁的蓝细菌中观察到的荧光猝灭的主要成分是由游离藻胆体与 IsiA 的偶联引起的。
Nonphotochemical quenching (NPQ) of excitation energy is a well-established phenomenon in green plants, where it serves to protect the photosynthetic apparatus from photodamage under excess illumination. The induction of NPQ involves a change in the function of the light- harvesting apparatus, with the formation of quenching centers that convert excitation energy into heat. Recently, a comparable phenomenon was demonstrated in cyanobacteria grown under iron-starvation. Under these conditions, an additional integral membrane chlorophyll-protein, IsiA, is synthesized, and it is therefore likely that IsiA is required for NPQ in cyanobacteria. We have previously used fluorescence recovery after photobleaching to show that phycobilisomes diffuse rapidly on the membrane surface, but are immobilized when cells are immersed in high- osmotic strength buffers, apparently because the interaction between phycobilisomes and reaction centers is stabilized. Here, we show that when cells of the cyanobacterium Synechocystis sp. PCC 6803 subjected to prolonged iron- deprivation are immersed in 1 M phosphate buffer, NPQ can still be induced as normal by high light. However, the formation of the quenched state is irreversible under these conditions, suggesting that it involves the coupling of free phycobilisomes to an integral- membrane complex, an interaction that is stabilized by 1 M phosphate. Fluorescence spectra are consistent with this idea. Fluorescence recovery after photobleaching measurements confirm that the induction of NPQ in the presence of 1 M phosphate is accompanied by immobilization of the phycobilisomes. We propose as a working hypothesis that a major component of the fluorescence quenching observed in iron- starved cyanobacteria arises from the coupling of free phycobilisomes to IsiA.