Responses of nine Trifolium repens L. populations to ultraviolet-B radiation: Differential flavonol glycoside accumulation and biomass production

Abstract

This study aimed to quantify and identify flavonoids involved in the response of nine populations of white clover (Trifolium repens L.) to ultraviolet-B radiation (UV-B). Plants were grown for 12 weeks in controlled environment rooms with or without supplemental UV-B radiation of 13.3 kJ m-2 d-1. Methanol-water extractable flavonoids were quantified using high performance liquid chromatography (HPLC). Two major peaks showed significant enhancement in the HPLC chromatogram in response to supplemental UV-B. The structures of the compounds responsible were identified by 1H and 13C nuclear magnetic resonance (NMR) spectroscopy to be the flavonols quercetin-3-O-β-D-xylopyranosyl-(1 → 2)-β-D-galactopyranoside and kaempferol-3-O-β-D-xylopyranosyl-(1 → 2)-β-D-galactopyranoside. With supplemental UV-B, quercetin glycoside levels increased on average by 200% while the kaempferol glycoside response was much smaller. Significant differences in flavonol accumulation were found among T. repens populations, both constitutively and in response to UV-B. Stress-adapted populations displayed particularly high flavonol levels under UV-B. There was an inverse correlation between plant productivity and quercetin accumulation. Furthermore, higher quercetin accumulation under UV-B was correlated with tolerance against UV-B-induced growth reduction. In conclusion, within-species comparisons in T. repens lend support to a distinct role for ortho-dihydroxylated flavonoids in the adaptation to UV-B stress and suggest particular advantages in this UV-B-induced biochemical adaptation for populations characterized by low habitat and plant productivity. (C) 2000 Annals of Botany Company.