Photosystem I cyclic electron flow via chloroplast NADH dehydrogenase-like complex performs a physiological role for photosynthesis at low light.

Wataru Yamori,Amane Makino,Toshiharu Shikanai

doi:10.1038/srep13908

Wataru Yamori, Amane Makino + Show 1 more

Open Access

https://doi.org/10.1038/srep13908

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Abstract

Cyclic electron transport around photosystem I (PS I) was discovered more than a half-century ago and two pathways have been identified in angiosperms. Although substantial progress has been made in understanding the structure of the chloroplast NADH dehydrogenase-like (NDH) complex, which mediates one route of the cyclic electron transport pathways, its physiological function is not well understood. Most studies focused on the role of the NDH-dependent PS I cyclic electron transport in alleviation of oxidative damage in strong light. In contrast, here it is shown that impairment of NDH-dependent cyclic electron flow in rice specifically causes a reduction in the electron transport rate through PS I (ETR I) at low light intensity with a concomitant reduction in CO2 assimilation rate, plant biomass and importantly, grain production. There was no effect on PS II function at low or high light intensity. We propose a significant physiological function for the chloroplast NDH at low light intensities commonly experienced during the reproductive and ripening stages of rice cultivation that have adverse effects crop yield.

Highlights

Regulation of photosynthetic electron transport in the thylakoid membrane of chloroplasts is fundamental for the maximum photosynthetic yield and plant growth
The present study showed that the impairment of NADH dehydrogenase-like (NDH)-dependent Cyclic electron transport did not cause any exacerbation of photoinhibition (Fig. 5), any alteration in photosynthetic parameters (i.e., electron transport rate through PS I (ETR I), electron transport rate (ETR) II, A390) (Fig. 4), and plant growth (Fig. 2) at high light intensity
At low light intensity, the defect in chloroplast NDH resulted in the reduction in ETR I without any effects on ETR II (Fig. 4), leading to a concomitant reduction in A390 (Fig. 4) and plant biomass and grain production (Fig. 3)

Summary

Introduction

Regulation of photosynthetic electron transport in the thylakoid membrane of chloroplasts is fundamental for the maximum photosynthetic yield and plant growth. The mutant phenotypes are rather mild and the mechanism that chloroplast NDH alleviates oxidative stresses is unclear because of the low rate of electron transport monitored in vivo and on isolated thylakoids[13,14]. Because light reactions limit photosynthesis at low light intensity, NDH-dependent PS I cyclic electron transport may play a role in energizing photosynthesis in low light. The role of NDH-dependent cyclic electron transport in photosynthesis and plant growth was studied in rice under both high and low light. We propose that cyclic electron transport around PS I via chloroplast NDH functions in efficient electron transport at low light intensity in rice

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