Abstract Cyclic electron flow (CEF) around photosystem I (PSI) is an important photoprotective mechanism, mediated mainly by PGR5/PGRL1 proteins and the chloroplast NAD(P)H dehydrogenase (NDH) complex. Here, chemical inhibition of PGR5/PGRL1- or NDH-dependent CEF was performed to determine their roles in preventing photoinhibition in tomato leaves under low night temperature (LNT) stress. Experimental treatments were with either antimycin A (A) or rotenone (R) to inhibit PGR5/PGRL1- or NDH-dependent CEF, respectively. The results showed that net photosynthetic rate (Pn), antioxidant enzyme activity, maximal photochemistry efficiency (Fv/Fm), effective photochemical quantum yield of PSII [Y(II)], non-photochemical quenching (NPQ), coefficient of photochemical fluorescence quenching (qP), and effective photochemical quantum yield of PSI [Y(I)] decreased more under LNT following A treatment than following R treatment. In A-treated plants, analysis of the normalized relative variable fluorescence at the K step (Vk) and the relative variable fluorescence at the J step (VJ) showed that both the donor and acceptor sides of PSII were severely damaged under LNT. Moreover, the donor side limitation of PSI [Y(ND)] increased whereas the acceptor side limitation of PSI [Y(NA)] decreased and the expression of genes encoding photosystem core subunits was significantly reduced. A treatment also resulted in increased ROS content and inhibition of SOD and APX activities under LNT. These data suggest that PGR5/PGRL1-dependent CEF plays a more important role than NDH-dependent CEF regarding resistance to LNT stress in tomato.

中文翻译：

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循环电子流在低夜间温度下保护番茄光系统 I 供体侧

摘要 光系统 I (PSI) 周围的循环电子流 (CEF) 是一种重要的光保护机制，主要由 PGR5/PGRL1 蛋白和叶绿体 NAD(P)H 脱氢酶 (NDH) 复合物介导。在这里，对 PGR5/PGRL1 或 NDH 依赖性 CEF 进行了化学抑制，以确定它们在防止低温 (LNT) 胁迫下番茄叶片光抑制中的作用。实验处理是用抗霉素 A (A) 或鱼藤酮 (R) 分别抑制 PGR5/PGRL1 或 NDH 依赖性 CEF。结果表明,净光合速率(Pn)、抗氧化酶活性、最大光化学效率(Fv/Fm)、PSII的有效光化学量子产率[Y(II)]、非光化学猝灭(NPQ)、光化学荧光猝灭系数(qP), LNT 处理后 PSI [Y(I)] 的有效光化学量子产率比 R 处理后降低更多。在 A 处理的植物中，对 K 步 (Vk) 的归一化相对可变荧光和 J 步 (VJ) 的相对可变荧光的分析表明，在 LNT 下，PSII 的供体和受体侧均受到严重破坏。此外，PSI [Y(ND)] 的供体侧限制增加，而 PSI [Y(NA)] 的受体侧限制减少，并且编码光系统核心亚基的基因的表达显着降低。处理还导致 ROS 含量增加和 LNT 下 SOD 和 APX 活性的抑制。这些数据表明，在番茄对 LNT 胁迫的抗性方面，PGR5/PGRL1 依赖性 CEF 比 NDH 依赖性 CEF 发挥更重要的作用。