Adaptive alterations in the activities of scavengers of active oxygen in cucumber cotyledons irradiated with UV-B

UV-B (290 - 320 nm) irradiation considerably reduced the cotyledon size of cucumber (Cucumis sativus L.) seedlings at 20 degrees C, and the extent of growth inhibition was reduced at 25 degrees C. At both temperatures, levels of endogenous scavengers and activities of active oxygen-scavenging enzymes were affected by UV-B irradiation. In particular, ascorbate peroxidase activity increased considerably, suggesting that active oxygen species might participate in the growth inhibition induced by UV-B irradiation. However, since no positive correlation was detected between the dependence of growth inhibition on temperature and the capacity to scavenge active species of oxygen, other mechanisms must be involved in the changes in the responses to UV-B that are related to temperature.