A Hard Day's Night: Diatoms Continue Recycling Photosystem II in the Dark
A Hard Day's Night: Diatoms Continue Recycling Photosystem II in the Dark
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辛苦的一天之夜：硅藻在黑暗中继续回收光系统 II
DOI：
10.3389/fmars.2016.00218
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发表时间：
2016-01-01
影响因子：
3.7
通讯作者：
Campbell，Douglas A.
中科院分区：
文献类型：
--
作者：
Li，Gang;Woroch，Amy D.;Campbell，Douglas A.
海洋硅藻具有光合作用，并在光线波动的环境中繁衍生息。像所有的产氧光合生物一样，硅藻面临光系统II复合物的光依赖性失活，光氧化水以产生生物合成还原剂。为了维持光合作用，这种光失活必须通过缓慢且代谢昂贵的蛋白质周转来抵消，这在蓝藻和植物中是光依赖的。我们跟踪每日周期的内容，合成和降解的光系统II，在一个小的和一个大的海洋硅藻，在低和高生长光水平。我们发现，与植物不同，硅藻即使在黑暗中也能维持光系统II蛋白的广泛循环。光系统II蛋白循环在低光下饱和，并在黑暗时期继续循环，使用来自呼吸的能量，允许硅藻赶上在前一个光照时期积累的过量光失活。大型硅藻只受到有限的光系统II的光失活，但光系统II蛋白的循环超过光系统II失活，因此大型硅藻在功能性光系统II单位失活之前将其清除。通过昼夜循环的活性光系统II中心和光系统II蛋白质的内容可预测地变化，但不相关，在给定的时间或生长条件下，总PSII的活性部分产生很大的变化。我们提出，黑暗和稳定的光系统II蛋白质的循环是由紧密整合的叶绿体和线粒体代谢的硅藻。这种基线的能力，持续的光系统II修复可能有助于硅藻在混合水环境中的成功，使它们从照明到黑暗再回来。
Marine diatoms are photosynthetic, and thrive in environments where light fluctuates. Like all oxygenic photosynthetic organisms diatoms face a light-dependent inactivation of the Photosystem II complexes that photooxidize water to generate biosynthetic reductant. To maintain photosynthesis this photoinactivation must be countered by slow and metabolically expensive protein turnover, which is light dependent in cyanobacteria and in plants. We tracked daily cycles of the content, synthesis and degradation of Photosystem II, in a small and in a large marine diatom, under low and high growth light levels. We show that, unlike plants, diatoms maintain extensive cycling of Photosystem II proteins even in the dark. Photosystem II protein cycling saturates at low light, and continued cycling in dark periods, using energy from respiration, allows the diatoms to catch up to excess photoinactivation accumulated over the preceding illuminated period. The large diatom suffers only limited photoinactivation of Photosystem II, but cycling of Photosystem II protein exceeds Photosystem II inactivation, so the large diatom recycles functional Photosystem II units before they are inactivated. Through the diel cycle the contents of active Photosystem II centers and Photosystem II proteins change predictably, but are not correlated, generating large changes in the fraction of total PSII that is active at a given time or growth condition. We propose that dark and steady cycling of Photosystem II proteins is driven by the tight integration of chloroplastic and mitochondrial metabolism in diatoms. This ability for baseline, continuous Photosystem II repair could contribute to the success of diatoms in mixed water environments that carry them from illumination to darkness and back.