Physiological and biochemical responses of Sorghum vulgare plants to supplemental ultraviolet-B radiation

Sorghum (Sorghum vulgare (Pers.) cv. MSH 51) plants were grown in the field under ambient and supplemental levels of ultraviolet-B radiation (UV-B; su pplemental daily dose corresponding to a 20% reduction in the stratospheric ozone column). Gas exchange characteristics, biomass, and levels of photos ynthetic pigments, flavonoids, catalase, peroxidase activity, and ascorbic acid were determined to evaluate the changes induced by enhanced levels of W-B irradiation. Gas exchange analysis indicated that one of the reasons fo r the decline in photosynthesis is stomatal limitation. Enhanced W-B also c aused reductions in chlorophyll and carotenoid pigments after 60 days of ex posure. Concentrations of UV-B absorbing pigments increased linearly with a ge. UV-B irradiation also increased phenolic compounds. Catalase activity d ecreased, while peroxidase activity increased in response to elevated UV-B. There was a decrease in total plant biomass and ascorbic acid content of p lants exposed to UV-B. Thus, an enhanced level of UV-B irradiation over a l ong period has a cumulative unfavourable effect on a number of physiologica l and biochemical processes, leading to a reduction in dry matter productio n.