CHANGES INDUCED BY ULTRAVIOLET-B (280-320 NM) RADIATION TO VEGETATIVEGROWTH AND PHOTOSYNTHETIC CHARACTERISTICS IN-FIELD GROWN VIGNA-UNGUICULATA L

The effect of ultraviolet-B (280-320 nm) radiation on growth and photo synthetic characteristics were investigated in field grown Vigna ungui culata L. Plants were grown at ambient and ambient plus a 1.8 kJ/m(2) supplementation of UV-B radiation for 25 days. The supplemental UV-B f luence used in this experiment simulated a 16% depletion in stratosphe ric ozone at midday in the summer at 10N latitude. Exposure to UV-B ra diation had increased the plant height, leaf area and leaf biomass. Th e level of total chlorophyll on a unit fresh weight basis showed margi nally decreased in the UV-B treated seedlings. No significant differen ce was seen in the concentration of UV-B absorbing compounds and RuBP case activity in UV-B treated seedlings. However, when various photosy nthetic activities were followed in isolated chloroplasts, UV-B enhanc ed radiation stimulated the whole chain, photosystem (PS) I and PS II activity during the first 5 days. Prolonged treatment under UV-B enhan ced radiation caused inhibition of the whole chain and the PS II activ ity. The artificial electron donor, Mn2+ failed to restore UV-B radiat ion induced loss of PS II activity, while DPC and NH2OH partially rest ored the PS II activity. (C) 1997 Elsevier Science Ireland Ltd.