University of Turku, Department of Biochemistry/Molecular Plant Biology, 20014 Turku, Finland.
Plant Cell Physiol. 2017 Dec 1;58(12):2217-2225. doi: 10.1093/pcp/pcx156.
Light-dependent electron transfer is necessary for photosynthesis, but light also damages PSII. Light-induced damage to PSII is called photoinhibition, and the damaging reactions of photoinhibition are still under debate. Diatoms possess an exotic combination of light-harvesting pigments, Chls a/c and fucoxanthin, making them an interesting platform for studying the photoreceptors of photoinhibition. We first confirmed the direct proportionality of photoinhibition to the photon flux density of incident light in the diatom Phaeodactylum tricornutum. Phaeodactylum is known for its efficient non-photochemical quenching, and the effect of this photoprotective mechanism on photoinhibition was tested. Photoinhibition proceeded essentially at the same rate in blue-light-grown Phaeodactylum cells that are capable of non-photochemical quenching and in red-light-grown, non-photochemical quenching-deficient cells. To obtain more insight into how the pigment composition of diatoms affects photoinhibition, we measured the action spectrum of photoinhibition in Phaeodactylum. In visible light, the action spectrum resembled the absorption spectrum of Phaeodactylum, and UV radiation caused much more photoinhibition than visible light. Comparison of the action spectrum of photoinhibition with the absorption spectrum and the excitation spectrum of 77 K PSII fluorescence emission confirmed that photosynthetic pigments are involved in photoinhibition, but the photoinhibitory efficiency of red light is weak, suggesting that the role of light-harvesting pigments as light receptors of photoinhibition is secondary. Finally, we compared photoinhibition in Phaeodactylum with that in other photosynthetic organisms, and our data indicate that the PSII reaction centers of Phaeodactylum are not particularly well protected against the primary damage of photoinhibition.
光依赖性电子转移对于光合作用是必要的，但光也会损坏 PSII。由光引起的 PSII 损伤称为光抑制，光抑制的损伤反应仍在争论中。硅藻具有独特的光捕获色素组合，Chls a/c 和岩藻黄素，使它们成为研究光抑制光受体的有趣平台。我们首先在菱形藻中证实了光抑制与入射光的光子通量密度之间的直接比例关系。菱形藻以其有效的非光化学猝灭而闻名，并且测试了这种光保护机制对光抑制的影响。在能够进行非光化学猝灭的蓝光生长的菱形藻细胞中和在红光生长的、缺乏非光化学猝灭的细胞中，光抑制基本上以相同的速率进行。为了更深入地了解硅藻的色素组成如何影响光抑制，我们在菱形藻中测量了光抑制的作用光谱。在可见光中，作用光谱与菱形藻的吸收光谱相似，而紫外辐射引起的光抑制比可见光多得多。将光抑制的作用光谱与吸收光谱和 77 K PSII 荧光发射的激发光谱进行比较，证实了光合色素参与了光抑制，但红光的光抑制效率较弱，这表明光捕获色素作为光抑制光受体的作用是次要的。最后，我们比较了菱形藻中的光抑制与其他光合生物中的光抑制，我们的数据表明，菱形藻的 PSII 反应中心对光抑制的初级损伤没有特别好的保护。
