Cyclic electron flow around photosystem I via chloroplast NAD(P)H dehydrogenase (NDH) complex performs a significant physiological role during photosynthesis and plant growth at low temperature in rice

Abstract

Summary: The role of NAD(P)H dehydrogenase (NDH)‐dependent cyclic electron flow around photosystem I in photosynthetic regulation and plant growth at several temperatures was examined in rice (Oryza sativa) that is defective in CHLORORESPIRATORY REDUCTION 6 (CRR6), which is required for accumulation of sub‐complex A of the chloroplast NDH complex (crr6). NdhK was not detected by Western blot analysis in crr6 mutants, resulting in lack of a transient post‐illumination increase in chlorophyll fluorescence, and confirming that crr6 mutants lack NDH activity. When plants were grown at 28 or 35°C, all examined photosynthetic parameters, including the CO 2 assimilation rate and the electron transport rate around photosystems I and II, at each growth temperature at light intensities above growth light (i.e. 800 μmol photons m−2 sec−1), were similar between crr6 mutants and control plants. However, when plants were grown at 20°C, all the examined photosynthetic parameters were significantly lower in crr6 mutants than control plants, and this effect on photosynthesis caused a corresponding reduction in plant biomass. The Fv/Fm ratio was only slightly lower in crr6 mutants than in control plants after short‐term strong light treatment at 20°C. However, after long‐term acclimation to the low temperature, impairment of cyclic electron flow suppressed non‐photochemical quenching and promoted reduction of the plastoquinone pool in crr6 mutants. Taken together, our experiments show that NDH‐dependent cyclic electron flow plays a significant physiological role in rice during photosynthesis and plant growth at low temperature.