Hydrogen Peroxide Mediates the Induction of Chloroplastic Ndh Complex under Photooxidative Stress in Barley

Chloroplast-encoded NDH polypeptides (components of the plastid Ndh complex) and the NADH dehydrogenase activity of the Ndh complex (NADH-DH) increased under photooxidative stress. The possible involvement of H(2)O(2)-mediated signaling in the photooxidative induction of chloroplastic ndh genes was thoroughly studied. We have analyzed the changes in the NADH-DH and steady-state levels of NDH-F polypeptide and ndhB and ndhF transcripts in barley (Hordeum vulgare cv Hassan) leaves. Subapical leaf segments were incubated in growing light (GL), photooxidative light (PhL), GL and H(2)O(2) (GL + H(2)O(2)), or PhL and 50 nm paraquat in the incubation medium. Treatments with H(2)O(2) under GL mimicked the photooxidative stimulus, causing a dose-dependent increase of NADH-DH and NDH-F polypeptide. The kinetic of Ndh complex induction was further studied in leaves pre-incubated with or without the H(2)O(2)-scavenger dimethyltiourea. NADH-DH and NDH-F polypeptide rapidly increased up to 16 h in PhL, GL+ H(2)O(2), and, at higher rate, in PhL and paraquat. The observed increases of NADH-DH and NDH-F after 4 h in PhL and GL + H(2)O(2) were not accompanied by significant changes in ndhB and ndhF transcripts. However, at 16-h incubations NADH-DH and NDH-F changes closely correlated with higher ndhB and ndhF transcript levels. All these effects were prevented by dimethylthiourea. It is proposed that the induction of chloroplastic ndh genes under photooxidative stress is mediated by H(2)O(2) through mechanisms that involve a rapid translation of pre-existing transcripts and the increase of the ndh transcript levels.