title: Cyclic electron flow may provide some protection against PSII photoinhibition in rice (Oryza sativa L.) leaves under heat stress.
abstract: Previously we have shown that a quick down-regulation in PSI activity compares to that of PSII following short-term heat stress for two rice groups including C4023 and Q4149, studied herein. These accessions were identified to have different natural capacities in driving cyclic electron flow (CEF) around PSI; i.e., low CEF (lcef) and high CEF (hcef) for C4023 and Q4149, respectively. The aim of this study was to investigate whether these two lines have different mechanisms of protecting photosystem II from photodamage under heat stress. We observed a stepwise alteration in the shape of Chl a fluorescence induction (OJIP) with increasing temperature treatment. The effect of 44°C treatment on the damping in Chl a fluorescence was more pronounced in C4023 than in Q4149. Likewise, we noted a disruption in the I-step, a decline in the Fvdue to a strong damping in the Fm, and a slight increase in the F0. Normalized data demonstrated that the I-step seems more susceptible to 44°C in C4023 than in Q4149. We also measured the redox states of plastocyanin (PC) and P700by monitoring the transmission changes at 820nm (I820), and observed a disturbance in the oxidation/reduction kinetics of PC and P700. The decline in the amplitude of their oxidation was shown to be about 29% and 13% for C4023 and Q4149, respectively. The electropotential component (Δφ) of ms-DLE appeared more sensitive to temperature stress than the chemical component (ΔpH), and the impact of heat was more evident and drastic in C4023 than in Q4149. Under heat stress, we noticed a concomitant decline in the primary photochemistry of PSII as well as in both the membrane energization process and the lumen protonation for both accessions, and it is evident that heat affects these parameters more in C4023 than in Q4149. All these data suggest that higher CET can confer higher photoprotection to PSII in rice lines, which can be a desirable trait during rice breeding, especially in the context of a "warming" world.
authors.affiliation: CAS-Key Laboratory for Computational Biology and State Key Laboratory for Hybrid Rice, Partner Institute for Computational Biology, Shanghai Institute for Biological Sciences, Chinese Academy of Sciences, Shanghai, China.
authors.forename: Jemaa
authors.initials: J
authors.lastname: Essemine
authors.affiliation: CAS-Key Laboratory for Computational Biology and State Key Laboratory for Hybrid Rice, Partner Institute for Computational Biology, Shanghai Institute for Biological Sciences, Chinese Academy of Sciences, Shanghai, China.
authors.forename: Yi
authors.initials: Y
authors.lastname: Xiao
authors.affiliation: CAS-Key Laboratory for Computational Biology and State Key Laboratory for Hybrid Rice, Partner Institute for Computational Biology, Shanghai Institute for Biological Sciences, Chinese Academy of Sciences, Shanghai, China.
authors.forename: Mingnan
authors.initials: M
authors.lastname: Qu
authors.affiliation: National Key Laboratory of Plant Molecular Genetics, Shanghai Institute of Plant Physiology and Ecology, Chinese Academy of Sciences, Shanghai, China.
authors.forename: Hualing
authors.initials: H
authors.lastname: Mi
authors.affiliation: CAS-Key Laboratory for Computational Biology and State Key Laboratory for Hybrid Rice, Partner Institute for Computational Biology, Shanghai Institute for Biological Sciences, Chinese Academy of Sciences, Shanghai, China. Electronic address: zhuxinguang@picb.ac.cn.
authors.forename: Xin-Guang
authors.initials: XG
authors.lastname: Zhu
mesh_terms: D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D003624:Darkness; D060146:Ecotype; D004579:Electron Transport; D005453:Fluorescence; D018869:Heat-Shock Response / Q000502:physiology*; D006358:Hot Temperature; D007700:Kinetics; D012275:Oryza / Q000502:physiology*; D055668:Photochemical Processes; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D018515:Plant Leaves / Q000502:physiology*; D011789:Quantum Theory; D013312:Stress, Physiological
chemical_list: D045332:Photosystem II Protein Complex; D002734:Chlorophyll; D000077194:Chlorophyll A
keywords: Cyclic electron flow; Fluorescence induction; Heat stress; Photoinhibition; Photosynthesis; Rice