Increases in surface flavonols and photosynthetic pigments in Gnaphalium luteo-album in response to UV-B radiation

Biochemical and physiological changes in Gnaphalium luteo-album plants were analysed in response to two different irradiance levels of UV-B. Low irradiance treatments showed increases in stem elongation, in chlorophyll A and B and carotenoid contents, and in the absorbance of vacuolar phenolics. Significant increases were observed in the concentrations of two surface flavonols, calycopterin and 3'-methoxycalycopterin, which were identified for the first time in this species. By contrast, a third surface flavonol, gnaphaliin, decreased in amount. High irradiance treatments inhibited plant growth but still increases in surface flavonols were observed. Our results support the view that surface flavonols are produced by plants as a protective device to shield the leaf from damage by UV-B radiation. (C) 1997 Elsevier Science Ltd. All rights reserved.