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Sci Rep. 2016 Feb 2;6:20147. doi: 10.1038/srep20147.

A physiological role of cyclic electron transport around photosystem I in sustaining photosynthesis under fluctuating light in rice.

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Center for Environment, Health and Field Sciences, Chiba University, 6-2-1 Kashiwa-no-ha, Kashiwa, Chiba 277-0882, Japan.
PRESTO, Japan Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan.
Department of Applied Plant Science, Graduate School of Agricultural Science, Tohoku University, 1-1 Tsutsumidori-Amamiyamachi, Aoba-ku, Sendai 981-8555, Japan.
CREST, JST, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan.
Department of Botany, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan.


Plants experience a highly variable light environment over the course of the day. To reveal the molecular mechanisms of their photosynthetic response to fluctuating light, we examined the role of two cyclic electron flows around photosystem I (CEF-PSI)--one depending on PROTON GRADIENT REGULATION 5 (PGR5) and one on NADH dehydrogenase-like complex (NDH)--in photosynthetic regulation under fluctuating light in rice (Oryza sativa L.). The impairment of PGR5-dependent CEF-PSI suppressed the photosynthetic response immediately after sudden irradiation, whereas the impairment of NDH-dependent CEF-PSI did not. However, the impairment of either PGR5-dependent or NDH-dependent CEF-PSl reduced the photosynthetic rate under fluctuating light, leading to photoinhibition at PSI and consequently a reduction in plant biomass. The results highlight that (1) PGR5-dependent CEF-PSI is a key regulator of rapid photosynthetic responses to high light intensity under fluctuating light conditions after constant high light; and (2) both PGR5-dependent and NDH-dependent CEF-PSI have physiological roles in sustaining photosynthesis and plant growth in rice under repeated light fluctuations. The highly responsive regulatory system managed by CEF-PSI appears able to optimize photosynthesis and plant growth under naturally fluctuating light conditions.

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