Abstract
Abstract Oat ( Avena sativa L. cv. Prevision) plants grown under high light intensity showed a decrease in the quantum yield of photosystem (PS) II, the capacity of photosynthetic electron transport and photochemical quenching, and an increase in non-photochemical quenching as consequence of the photoinhibition of PS II. PS I was more stable than PS II in oat plants exposed to strong light treatments, probably because it plays a photoprotective role though cyclic electron flow. PS I photoinhibition was only observed after 10 photoperiods of high light intensity, as revealed by decreased PS I activity and the degradation of PSI A/B protein. However, PS I was more sensitive to photoinhibition in the presence of antimycin A, which is an inhibitor of one pathway of the cyclic electron transport. Immunoblot analysis using a specific antibody against the NdhH subunit of the thylakoidal NADH dehydrogenase (NADH DH) complex revealed an increase in the amount of this subunit in response to photoinhibitory conditions. Additionally, an increase in NADH dehydrogenase activity in the stroma thylakoids was also observed under these conditions. Treatment with 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), which stimulates the cyclic electron flow, decreased the maximal quantum yield of PSII ( Φ PS II) and caused an increase in PSI and NADH dehydrogenase activities of the stroma thylakoids. Treatment with antimycin A under high light intensity also caused an increase in the NADH dehydrogenase activity of the stroma thylakoids. The results are in agreement with an increase of the thylakoidal NADH dehydrogenase complex and a stimulation of the cyclic electron flow involving the thylakoidal complex in response to photoinhibition conditions.
Published Version
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