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Title: Impact of Solar Ultraviolet-B Radiation on the Antioxidant Defense System in Soybean Lines Differing in Flavonoid Contents

item Natarajan, Savithiry - Savi

Submitted to: Environmental and Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/20/2007
Publication Date: 10/20/2007
Citation: Xu, C., Natarajan, S.S., Sullivan, J.H. 2007. Impact of Solar Ultraviolet-B Radiation on the Antioxidant Defense System in Soybean Lines Differing in Flavonoid Contents. Environmental and Experimental Botany. 63:39-48.

Interpretive Summary: Since the early 1970's, there has been growing concern about the possible harmful effects of increases in ultraviolet-B (UV-B) light due to ozone reduction in the earth's upper atmosphere. Increased UV-B light has caused significant stress to plants in terms of poor yield and harmful mutations. Most of the earlier experiments examining the UV-B effects on plant physiological changes were conducted indoors. Under these conditions the UV-B effects were overestimated. In the work reported here the effects of solar UV-B light were studied under field conditions by comparing two similar soybean varieties which contain different amounts of compounds (antioxidants) that block the effect of UV-B light. This study showed that solar UV-B light caused stress in both types of soybean plants and that antioxidants can act as screening compounds to protect plants from ultraviolet light. This work also showed that solar ultraviolet-A light might cause harmful effects in plants. This work demonstrates the importance of antioxidants in UV protection in plants growing under field condition. The findings should be of interest to researchers who are involved in investigating the UV-B effects on plant physiology and will be useful for breeders developing more UV resistant soybeans.

Technical Abstract: Exposure to ultraviolet-B (UV-B) radiation can lead to oxidative damage in plants. However, UV protection may be enhanced by increased production or activities of antioxidants. In the present study two isolines of soybean Clark cultivar, the normal line with moderate levels of flavonoids and the magenta line with reduced flavonoids levels, were grown in the field with or without natural levels of UVB. The primary leaves were harvested for analysis of active oxygen species (AOS). Solar UV-B radiation caused oxidative stress in both lines, and affect AOS metabolism mainly by decreasing the superoxide dismutase activity and increasing the activities of ascorbate peroxidase, catalase, and glutathione reductase, resulting in decreased ascorbic acid content and increased dehydroascorbate content. The magenta line had greater oxidative stress than the normal line, in spite of its enhanced oxidative defense capacity as compared to the normal line, even under UV-B exclusion. The enhanced responses in the magenta line are likely due to increased penetration of solar ultraviolet-A photos through its more transparent epidermis.