Department of Biological Sciences, School of Science, The University of Tokyo, 7‑3‑1 Hongo, Bunkyo‑ku, Tokyo, 113‑0033, Japan.
Division of Plant Sciences, Research School of Biology, The Australian National University, Acton, ACT, 2601, Australia.
Photosynth Res. 2021 Aug;149(1-2):83-92. doi: 10.1007/s11120-020-00805-z. Epub 2021 Jan 6.
Light energy causes damage to Photosystem I (PSI) and Photosystem II (PSII). The majority of the previous photoinhibition studies have been conducted with PSII, which shows much larger photoinhibition than PSI; therefore, relatively little is known about the mechanism of PSI photoinhibition so far. A previous report showed that the photoinhibition action spectrum measured with PSI activity of isolated thylakoid is similar to the absorption spectrum of chlorophyll. However, it is known that the extent of PSI photoinhibition is much smaller in vivo compared to in vitro. It is also possible that the different extent of PSII photoinhibition, caused by different spectral light qualities, can affect the photoinhibition of PSI in vivo because PSI receives electrons from PSII. In the present research, to study the effect of light quality and the effect of the extent of PSII photoinhibition on the PSI photoinhibition in vivo, intact leaves were photoinhibited under four different light qualities. The rate coefficient of PSI photoinhibition was significantly higher in blue and red light compared to white light. The rate of PSI photoinhibition at the same photon-exposure was the largest in blue and red light and followed by white and green light. These results support the notion that light absorption by chlorophyll is responsible for the PSI photoinhibition, even in intact leaves. The variation among light colors in the relationships between the extent of photoinhibition of PSII and that of PSI indicate that PSI and PSII are independently photoinhibited with different mechanisms in the early stage of in vivo photoinhibition.
光能会对光系统 I（PSI）和光系统 II（PSII）造成损伤。之前的大部分光抑制研究都是针对 PSII 进行的，结果表明 PSII 的光抑制作用比 PSI 大得多；因此，到目前为止，人们对 PSI 光抑制的机制知之甚少。之前的一份报告表明，用分离类囊体的 PSI 活性测量的光抑制作用光谱与叶绿素的吸收光谱相似。然而，众所周知，与体外相比，PSI 在体内的光抑制程度要小得多。也有可能是不同光谱光质引起的 PSII 光抑制程度不同，会影响 PSI 在体内的光抑制，因为 PSI 从 PSII 接收电子。在本研究中，为了研究光质的影响以及 PSII 光抑制程度对 PSI 体内光抑制的影响，用四种不同的光质对完整叶片进行光抑制处理。与白光相比，蓝光和红光下 PSI 光抑制的速率系数明显更高。在相同光子暴露下，PSI 光抑制的速率在蓝光和红光下最大，其次是白光和绿光。这些结果支持了这样一种观点，即即使在完整叶片中，叶绿素的光吸收也会导致 PSI 光抑制。在 PSII 光抑制程度与 PSI 光抑制程度之间的关系中，不同颜色光之间的变化表明，在体内光抑制的早期阶段，PSI 和 PSII 以不同的机制独立地发生光抑制。
