Effects of ultraviolet-B enhanced radiation and temperature on growth and photochemical activities in Vigna unguiculata

Changes in growth characteristics and photochemical activities in Vigna unguiculata L. Walp seedlings maintained at constant temperature of 10, 20, 30 and 40 degrees C under control and ultraviolet-B enhanced radiation (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 also observed with respect to changes in leaf fresh and dry masses and total chlorophyll (Chi) content under these temperatures. At 10 degrees C the total Chl content was 3-fold higher under the treatment than under control conditions. In seedlings growing at 20 and 30 degrees C the overall photosynthetic electron transport (H2O --> methyl viologen) showed a significant enhancement during the 36-h W-B treatment and thereafter a gradual reduction. Although a similar trend was found in photosystem 1 (PS1), the inhibition even after 60 h of UV-B treatment was not statistically significant. Photosystem 2 (PS2) activity was inhibited in seedlings treated for 60 h by UV-B at 20 and 30 degrees C. However, no inhibition was observed at 40 degrees C. No detectable photochemical activity was found in seedlings grown at 10 degrees C under either control or UV-B enhanced irradiation although the chloroplasts contained Chl.