Sugar Beet (Beta vulgaris L) Phytochemical Alterations in Response to Ultraviolet-B Radiation

All living organisms have mechanisms to deal with the harmful effects of ultraviolet (UV) radiation. In this study, the effects of three UV-B doses on some physiological properties of sugar beet cultivar, BR1 was evaluated in a completely randomized design with three replications. All plants were kept in a growth chamber at 25/20 ºC (day/night) with a 16 hours light and 8hours dark photoperiod for 30days. Then, plants were divided into 4 groups including control and three experimental groups exposed to 3.042, 6.084 and 9.126 KJm-2d-1UV-B radiation, respectively for one week. Results indicated that the highest amount of UV-B (9.126 KJm-2d-1) induced an 11% reduction in soluble sugar content of the leaf tissue. Treatment with 3.042, 6.084 and 9.126 KJm-2d-1UV-B resulted in 80, 82, and 86% increase in flavonoids content, respectively. Moreover, the highest amount of UV-B caused a 24% increase in total phenolic compounds content. Furthermore, UV-B radiation caused a significant increase in amounts of betalains (betanin and betaxanthin). The antioxidant activity of leaf methanolic extract increased under UV-B radiation. Evaluation of betaninand betaxanthin antioxidant activity also revealed that these pigments cause α, α-diphenyl-β-picrylhydrazyl free radical inhibition and betaxanthinhasa higher antioxidant activity than betanin. Increase in UV irradiation intensity increased the secondary metabolites and, consequently, increased the antioxidant capacity of the crop.