Department of Life Technologies/Molecular Plant Biology, University of Turku, Turku, Finland.
Physiol Plant. 2022 Nov;174(6):e13824. doi: 10.1111/ppl.13824.
Photosynthetic organisms, like evergreen plants, may encounter strong light at low temperatures. Light, despite being the energy source of photosynthesis, irreversibly damages photosystem II (PSII). We illuminated plant thylakoid membranes and intact cyanobacterial cells at -78.5°C and assayed PSII activity with oxygen evolution or chlorophyll fluorescence, after thawing the sample. Both UV radiation and visible light damaged PSII of pumpkin (Cucurbita maxima) thylakoids at -78.5°C, but visible-light-induced photoinhibition at -78.5°C, unlike at +20°C, proceeded only in the presence of oxygen. A strong magnetic field that would decrease triplet chlorophyll formation by recombination of the primary radical pair slowed down photoinhibition at -78.5°C, suggesting that singlet oxygen produced via recombination of the primary pair is a major contributor to photoinhibition at -78.5°C. However, a magnetic field did not affect singlet oxygen production at +25°C. Thylakoids of winter leaves of an evergreen plant, Bergenia, were less susceptible to photoinhibition both at -78.5°C and +20°C, contained high amounts of carotenoids and produced little singlet oxygen (measured at +20°C), compared to thylakoids of summer leaves. In contrast, high carotenoid amount and low singlet oxygen yield did not protect a Synechocystis mutant from photoinhibition at -78.5°C. Thylakoids isolated from Arabidopsis thaliana grown under high light, which reduces PSII antenna size, were more resistant than control plants against photoinhibition at -78.5°C but not at +20°C, although carotenoid amounts were similar. The results indicate that visible-light-induced photoinhibition at -78.5°C depends on singlet oxygen, whereas photoinhibition at +20°C is largely independent of oxygen.
光合作用生物，如常绿植物，可能会在低温下遇到强光。光虽然是光合作用的能量来源，但会不可逆地破坏光系统 II（PSII）。我们在-78.5°C 下照射植物类囊体膜和完整的蓝藻细胞，并在样品解冻后通过氧气释放或叶绿素荧光来测定 PSII 活性。在-78.5°C 下，紫外线和可见光都会破坏南瓜（Cucurbita maxima）类囊体的 PSII，但与+20°C 不同的是，可见光诱导的-78.5°C 下的光抑制只有在氧气存在的情况下才会发生。一个强磁场可以通过初级自由基对的重组来减少三线态叶绿素的形成，从而减缓-78.5°C 下的光抑制，这表明通过初级对的重组产生的单线态氧是-78.5°C 下光抑制的主要原因。然而，磁场不会影响+25°C 下的单线态氧产生。与夏季叶片相比，常绿植物 Bergenia 冬季叶片的类囊体在-78.5°C 和+20°C 下都不易受到光抑制，类囊体中含有大量的类胡萝卜素，产生的单线态氧较少（在+20°C 下测量）。相比之下，高类胡萝卜素含量和低单线态氧产量并不能保护 Synechocystis 突变体免受-78.5°C 下的光抑制。与对照植物相比，在高光下生长的拟南芥（Arabidopsis thaliana）类囊体在-78.5°C 下对光抑制的抵抗力更强，这会降低 PSII 天线的大小，但在+20°C 下则不然，尽管类胡萝卜素含量相似。结果表明，-78.5°C 下可见光诱导的光抑制依赖于单线态氧，而+20°C 下的光抑制在很大程度上与氧气无关。
