Changes induced by ultraviolet-B (280-320 nm) radiation to vegetative growth and photosynthetic characteristics in field grown Vigna unguiculata L

The effect of ultraviolet-B (280-320 nm) radiation on growth and photosynthetic characteristics were investigated in field grown Vigna unguiculata 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 fluence used in this experiment simulated a 16% depletion in stratospheric ozone at midday in the summer at 10N latitude. Exposure to UV-B radiation had increased the plant height, leaf area and leaf biomass. The level of total chlorophyll on a unit fresh weight basis showed marginally decreased in the UV-B treated seedlings. No significant difference was seen in the concentration of UV-B absorbing compounds and RuBP case activity in UV-B treated seedlings. However, when various photosynthetic activities were followed in isolated chloroplasts, UV-B enhanced radiation stimulated the whole chain, photosystem (PS) I and PS II activity during the first 5 days. Prolonged treatment under UV-B enhanced radiation caused inhibition of the whole chain and the PS II activity. The artificial electron donor, Mn2+ failed to restore UV-B radiation induced loss of PS II activity, while DPC and NH2OH partially restored the PS II activity. (C) 1997 Elsevier Science Ireland Ltd.