Photomorphogenic effects of UV-B radiation and a-Tocopherol on Brassica rapa.

Abstract

UV-B radiation may cause morphological, physiological, and genetic damage to living organisms. Prolonged exposure to UV-B radiation causes photooxidative damage to DNA and proteins. Sessile organisms, such as plants, are unable to escape relentless UV-B exposure. However, plants can protect themselves from UV-B by the production of antioxidants. Plants also respond to UV-B irradiance by inhibiting hypocotyl elongation, reducing number of leaves and developing fewer flowers. In this study, Brassica rapa was subjected to varying degrees of UV-B radiation and treated with a lipid-soluble antioxidant, α-tocopherol. Harmful reactive oxygen species, formed by UV-B radiation, may be stabilized by α-tocopherol. The hypothesis are that B. rapa will develop differently under UV-B treatment and B. rapa treated with UV-B and α-tocopherol will develop differently compared to B. rapa exposed to UV-B without α-tocopherol. In the experiment, two strains (RBr – standard rapid-cycling and ygr – yellow-green mutation) of B. rapa received no UV-B, ambient UV-B, or high UV-B exposure. Plants received a treatment of either α-tocopherol or water. UV-B fluorescent light (280-320 nm) and photosynthetically active radiation (PAR, 400-700 nm) sources were suspended above the plants. Measurements were taken to determine chlorophyll content, stem height, leaf surface area, and total biomass. Brassica rapa was found to be susceptible to UV-B radiation which resulted in shortened height, and fewer leaves and flowers. Ygr that received α-tocopherol produced more flowers under ambient UV-B exposure when compared to RBr. The external application of α-tocopherol on plants may have promoted repair mechanisms in the presence of UV-B radiation.