Effects of salicylic acid on UV-B-induced oxidative stress and ultrastructure of leaves in cucumber seedlings

Cucumber (Cucumis sativus L.) seedlings were irradiated or not irradiated with UV-B for several days in environment controled growth chambers. The first leaves irradiated with UV-B were retarded in growth but simultaneously acquired a remarkably high tolerence to oxidative stress, as induced by SA treatment, compared with the non irradiated leaves. Observed within 1 d after the start of UV-B and was maintained during the 5 d period of UV-B treatment. There were low rates of growth and photosynthesis in cucumber plants when treated with SA, suggesting alterations in anatomy and ultrastructure organisation of chloroplasts. Exogenous application of SA diminished chloroplast photosynthetic activity.