Low concentrations of NaHSO3 enhance NAD(P)H dehydrogenase-dependent cyclic photophosphorylation and alleviate the oxidative damage to improve photosynthesis in tobacco

Abstract

Bisulfite at low concentrations (L-NaHSO3) increases cyclic electron transport around photosystem I (PSI) and photosynthesis. However, little is known regarding the detailed contribution of cyclic electron transport to the promoted photosynthesis by L-NaHSO3. In the present work, we used tobacco mutant defective in ndhC-ndhK-ndhJ (ΔndhCKJ) to investigate the role of NAD(P)H dehydrogenase (NDH)-dependent cyclic electron transport around PSI in an increase in photosynthesis by L-NaHSO3. After the treatment of tobacco leaves with L-NaHSO3 (10 μmol L−1), the NDH-dependent cyclic electron transport, monitored by a transient post-illumination increase in Chl fluorescence and the amount of NDH, was notably up-regulated in wild type (WT). The NDH-dependent cyclic electron transport was severely impaired in ΔndhCKJ and was not significantly affected by treatment with L-NaHSO3. Accordingly, the NDH-dependent transthylakoid membrane proton gradient (ΔpH), as reflected by the slow phase of millisecond-delayed light emission (ms-DLE), was increased by L-NaHSO3 in WT, but not in ΔndhCKJ; the enhancement of cyclic photophosphorylation (PSP) activity by L-NaHSO3 was more obvious in WT than ΔndhCKJ. The accumulation of both superoxide and hydrogen peroxide was reduced in WT when subjected to L-NaHSO3 treatment, but not in ΔndhCKJ. Furthermore, the increase of photosynthetic O2 evolution rate by L-NaHSO3 was more significant in WT than in ΔndhCKJ. We therefore conclude that L-NaHSO3 alleviates the photo-oxidative damage by the enhancement of NDH-dependent cyclic PSP, thereby improving photosynthesis.