ADAPTIVE ALTERATIONS IN THE ACTIVITIES OF SCAVENGERS OF ACTIVE OXYGENIN CUCUMBER COTYLEDONS IRRADIATED WITH UV-B

UV-B (290 - 320 nm) irradiation considerably reduced the cotyledon siz e of cucumber (Cucumis sativus L.) seedlings at 20 degrees C, and the extent of growth inhibition was reduced at 25 degrees C. At both tempe ratures, levels of endogenous scavengers and activities of active oxyg en-scavenging enzymes were affected by UV-B irradiation. In particular , ascorbate peroxidase activity increased considerably, suggesting tha t active oxygen species might participate in the growth inhibition ind uced by UV-B irradiation. However, since no positive correlation was d etected between the dependence of growth inhibition on temperature and the capacity to scavenge active species of oxygen, other mechanisms m ust be involved in the changes in the responses to UV-B that are relat ed to temperature.