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The influence of short-term changes in ambient UV-B radiation on barley, corn and soybean.
Sullivan, Joe*,1, Gitz, Dennis2, Liu-Gitz, Lan1, 1 University of Maryland, College Park, MD2 USDA, Beltsville, MD
ABSTRACT- A substantial number of studies have been conducted over the last several decades in order to assess the potential impacts of long-term increases in UV-B radiation (UV-B between 280-320 nm) that might result from continued depletion of stratospheric ozone. However, in addition to stratospheric ozone levels and seasonal changes, tropospheric conditions such as cloudiness exert a much larger influence on short-term fluctuations in levels of ambient UV-B received a given location. The effects of short-term changes in UV-B radiation on plant growth, phytochemistry and physiological processes have received relatively little attention in the literature. Barley (Hordeum vulgare), soybean (Glycine max) and corn (Zea maize) were grown under either near ambient levels of UV-B or under reduced levels (ca 90% reduction) in the field. Periodic measurements on leaf phytochemistry, photosynthetic integrity (Fv/Fm) and levels of DNA damage were made following contrasting periods of ambient levels of UV-B in order to test whether development and subsequent sensitivity to UV-B radiation was altered by short-term variation in UV-B. Ambient levels of UV-B modulated the levels of flavonoids and other putative UV-screening compounds in barley. These in turn exerted some influence on the levels of DNA dimmers induced by subsequent exposure to UV-B radiation with higher flavonoid levels providing the expected greater degree of protection to those plants. Soybean and corn both exhibited reduced levels of Fv/Fm under higher total solar irradiance received the previous day before measurements but the contribution of UV-B was negligible in corn and cultivar specific in soybean. These examples suggest that daily changes in UV-B can alter subsequent sensitivity to UV-B in terms of DNA damage and potential photosynthetic efficiency in some species.
Key words: flavonoids, UV-B radiation, photoinhibition