Low concentrations of NaHSO_3 enhance NAD(P)H dehydrogenasedependent cyclic photophosphorylation and alleviate the oxidative damage to improve photosynthesis in tobacco

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(ndhCKJ) 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 ndhCKJ and was not significantly affected by treatment with L-NaHSO3.Accordingly,the NDH-dependent transthylakoid membrane proton gradient(pH),as reflected by the slow phase of millisecond-delayed light emission(ms-DLE),was increased by L-NaHSO3 in WT,but not in ndhCKJ;the enhancement of cyclic photophosphorylation(PSP) activity by L-NaHSO3 was more obvious in WT than ndhCKJ.The accumulation of both superoxide and hydrogen peroxide was reduced in WT when subjected to L-NaHSO3 treatment,but not in ndhCKJ.Furthermore,the increase of photosynthetic O 2 evolution rate by L-NaHSO3 was more significant in WT than in ndhCKJ.We therefore conclude that L-NaHSO3 alleviates the photo-oxidative damage by the enhancement of NDH-dependent cyclic PSP,thereby improving photosynthesis.

Bisulfite at low concentrations （L-NaHSO3） increases cyclic electron transport around photosystem l （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 （AndhCKJ） 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 ~rnol L-I）, 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 AndhCKJ and was not significantly affected by treatment with L-NaHSO3. Accordingly, the NDH-dependent transthylakoid membrane proton gradient （ApH）, as reflected by the slow phase of millisecond-delayed light emission （ms-DLE）, was increased by L-NaHSO3 in WT, but not in AndhCKJ; the enhancement of cy- clic photophosphorylation （PSP） activity by L-NaHSO3 was more obvious in WT than AndhCKJ. The accumulation of both su- peroxide and hydrogen peroxide was reduced in WT when subjected to L-NaHSO3 treatment, but not in AndhCKJ. Furthermore, the increase of photosynthetic 02 evolution rate by L-NaHSO3 was more significant in WT than in AndhCKJ. We therefore con- clude that L-NaHSO3 alleviates the photo-oxidative damage by the enhancement of NDH-dependent cyclic PSP, thereby improv- ing photosynthesis.