EFFECTS OF ULTRAVIOLET-B ENHANCED RADIATION AND TEMPERATURE ON GROWTHAND PHOTOCHEMICAL ACTIVITIES IN VIGNA-UNGUICULATA

Changes in growth characteristics and photochemical activities in Vign a unguiculata L. Walp seedlings maintained at constant temperature of 10, 20, 30 and 40 degrees C under control and ultraviolet-B enhanced r adiation (UV-B) were investigated. UV-B retarded the shoot elongation and also leaf expansion to a great extent at 30 degrees C but produced only marginal changes at 20 and 40 degrees C. Similar response was al so observed with respect to changes in leaf fresh and dry masses and t otal chlorophyll (Chi) content under these temperatures. At 10 degrees C the total Chl content was 3-fold higher under the treatment than un der control conditions. In seedlings growing at 20 and 30 degrees C th e overall photosynthetic electron transport (H2O --> methyl viologen) showed a significant enhancement during the 36-h W-B treatment and the reafter a gradual reduction. Although a similar trend was found in pho tosystem 1 (PS1), the inhibition even after 60 h of UV-B treatment was not statistically significant. Photosystem 2 (PS2) activity was inhib ited in seedlings treated for 60 h by UV-B at 20 and 30 degrees C. How ever, no inhibition was observed at 40 degrees C. No detectable photoc hemical activity was found in seedlings grown at 10 degrees C under ei ther control or UV-B enhanced irradiation although the chloroplasts co ntained Chl.