Essemine Jemaa, Qu Mingnan, Mi Hualing, Zhu Xin-Guang
CAS Key Laboratory of Computational Biology, CAS-MPG Partner Institute for Computational Biology, Shanghai Institute for Biological Sciences, Chinese Academy of Sciences Shanghai, China.
National Key Laboratory of Plant Molecular Genetics, Shanghai Institute of Plant Physiology and Ecology, Chinese Academy of Sciences Shanghai, China.
Front Plant Sci. 2016 Mar 30;7:383. doi: 10.3389/fpls.2016.00383. eCollection 2016.
Cyclic electron flow (CEF) around photosystem I (PSI) can protect photosynthetic electron carriers under conditions of stromal over-reduction. The goal of the research reported in this paper was to investigate the responses of both PSI and photosystem II (PSII) to a short-term heat stress in two rice lines with different capacities of cyclic electron transfer, i.e., Q4149 with a high capacity (hcef) and C4023 with a low capacity (lcef). The absorbance change at 820 nm (ΔA820) was used here to assess the charge separation in the PSI reaction center (P700). The results obtained show that short-term heat stress abolishes the ferredoxin-quinone oxidoreductase (FQR)-dependent CEF in rice and accelerates the initial rate of P700 (+) re-reduction. The P700 (+) amplitude was slightly increased at a moderate heat-stress (35°C) because of a partial restriction of FQR but it was decreased following high heat-stress (42°C). Assessment of PSI and PSII activities shows that PSI is more susceptible to heat stress than PSII. Under high temperature, FQR-dependent CEF was completely removed and NDH-dependent CEF was up-regulated and strengthened to a higher extent in C4023 than in Q4149. Specifically, under normal growth temperature, hcef (Q4149) was characterized by higher FQR- and chloroplast NAD(P)H dehydrogenase (NDH)-dependent CEF rates than lcef (C4023). Following thermal stress, the activation of NDH-pathway was 130 and 10% for C4023 and Q4149, respectively. Thus, the NDH-dependent CEF may constitute the second layer of plant protection and defense against heat stress after the main route, i.e., FQR-dependent CEF, reaches its capacity. We discuss the possibility that under high heat stress, the NDH pathway serves as a safety valve to dissipate excess energy by cyclic photophosphorylation and overcome the stroma over-reduction following inhibition of CO2 assimilation and any shortage or lack in the FQR pathway. The potential role of the NDH-dependent pathway during the evolution of C4 photosynthesis is briefly discussed.
围绕光系统I（PSI）的循环电子流（CEF）可以在基质过度还原的条件下保护光合电子载体。本文报道的研究目的是调查具有不同循环电子传递能力的两个水稻品系，即高循环电子流能力（hcef）的Q4149和低循环电子流能力（lcef）的C4023中，PSI和光系统II（PSII）对短期热胁迫的响应。此处使用820 nm处的吸光度变化（ΔA820）来评估PSI反应中心（P700）中的电荷分离。所得结果表明，短期热胁迫消除了水稻中依赖铁氧还蛋白-醌氧化还原酶（FQR）的CEF，并加快了P700（+）再还原的初始速率。在中等热胁迫（35°C）下，由于FQR受到部分限制，P700（+）幅度略有增加，但在高热胁迫（42°C）后则降低。对PSI和PSII活性的评估表明，PSI比PSII对热胁迫更敏感。在高温下，依赖FQR的CEF被完全消除，依赖NDH的CEF在C4023中比在Q4149中上调并增强的程度更高。具体而言，在正常生长温度下，hcef（Q4149）的特征是依赖FQR和叶绿体NAD（P）H脱氢酶（NDH）的CEF速率高于lcef（C4023）。热胁迫后，C4023和Q4149中NDH途径的激活率分别为130%和10%。因此，依赖NDH的CEF可能在主要途径，即依赖FQR的CEF达到其容量后，构成植物抵御热胁迫的第二层保护和防御。我们讨论了在高热胁迫下，NDH途径作为安全阀通过循环光合磷酸化消散多余能量并克服CO2同化受抑制以及FQR途径中任何短缺或缺乏后基质过度还原的可能性。还简要讨论了NDH依赖途径在C4光合作用进化过程中的潜在作用。
