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

Wataru Yamori,Toshiharu Shikanai,Amane Makino

doi:10.1038/srep20147

Abstract

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.

Highlights

The Cyt b6/f complex, can generate a Δ pH across the thylakoid membrane, and produces ATP but without any accumulation of NADPH in chloroplasts[2]
CEF-PSI consists of two partly redundant pathways: the main pathway depends on the PGR5 (PROTON GRADIENT REGULATION 5) and PGRL1 (PGR5-LIKE PHOTOSYNTHETIC PHENOTYPE 1) proteins[3,4], whereas the minor pathway is mediated by the chloroplast NADH dehydrogenase-like (NDH) complex[5,6]
When plants were grown at a constant light intensity of 500 μ mol photons m–2 s–2 with a 14-h photoperiod, contents of leaf nitrogen, rubisco, and chlorophyll per unit leaf area and the chlorophyll-a/b ratio were similar among WT plants, PGR5 KD plants, and crr[6] mutant plants (Table 1)

Summary

Introduction

The Cyt b6/f complex, can generate a Δ pH across the thylakoid membrane, and produces ATP but without any accumulation of NADPH in chloroplasts[2]. Recent studies showed that fluctuating light induced photodamage in PSI and severely retarded the growth in pgr[5] plants[8,9,10]. These results indicate that PGR5 is essential for survival under field conditions in Arabidopsis. The mutant phenotypes tested are mild, and the mechanism by which chloroplast NDH might alleviate oxidative stresses is unclear because of the low rate of electron transport monitored in vivo and in isolated thylakoids[16,17]. We examined the physiological role of PGR5-dependent and NDH-dependent CEF-PSI in photosynthetic regulation and plant growth under fluctuating light in rice (Oryza sativa L.), a high-light-adaptive major crop. PGR5-dependent and NDH-dependent cyclic electron transport is essential for photoprotection of PSI under fluctuating light in rice

Methods

Results

Conclusion