EFFECT OF ENHANCED UV-B RADIATION ON GERMINATION, SEEDLING GROWTH AND BIOCHEMICAL RESPONSES OF VIGNA MUNGO (L.) HEPPER

The study focuses on the effect of supplemental UV-B radiation on germination, seedling growth, chlorophyll a and b contents, soluble phenols, anthocyanins, flavones contents, phenylalanine ammonia lyase (PAL) activity and tyrosine ammonia lyase (TAL) activity of mash-bean (Vigna mungo (L.) Hepper.). Even though the germination velocity was substantially increased, the final germination percentage remained significantly suppressed by UV-irradiance. Both root and shoot growth of the seedlings were markedly reduced by enhanced UV-B radiation. UV-B irradiation substantially decreased both chlorophylls a and b and the total amount of chlorophyll a plus b compared to controls. However, chlorophyll a/b ratio was generally elevated. Remarkable accumulation of total soluble phenols occurred in response to UV-B radiation. PAL activity increased markedly as a result of UV-stress in the beginning, subsequently, however, it declined, whereas, TAL activity consistently increased over the controls following UV-B irradiation up to 8 days of treatment. The levels of anthocyanins and flavones increased in treatments over the controls as they provide a protective mechanism to UV-B radiations. In general, the growth and physiological responses to UV-B radiation were more pronounced at greater exposure period.