Identification of the product of ndhA gene as a thylakoid protein synthesized in response to photooxidative treatment.

A 76 amino acid sequence of NDH-A (the protein encoded by plastid ndhA gene) from barley (Hordeum vulgare L.) was expressed as a fusion protein with beta-galactosidase in E. coli. The corresponding antibody generated in rabbits was used to investigate localization, expression and synthesis in vitro of NDH-A. NDH-A was identified as a 35 kDa polypeptide localized in thylakoid membrane. Western blots shows a large increase in NDH-A levels when barley leaves were incubated under photooxidative conditions, which was more pronounced in mature-senescent leaves than in young leaves. Immunoprecipitation of the [35S]methionine labelled proteins, synthesized in vitro by isolated chloroplasts, demonstrated the synthesis in chloroplasts of the NDH-A 35 kDa polypeptide when barley leaves had been incubated under photooxidative conditions. The results indicate that ndh genes may be involved in the protection of chloroplasts against photooxidative stress, particularly in mature-senescent leaves.