Responses of Nine Trifolium repens L. Populations to Ultraviolet-B Radiation: Differential Flavonol Glycoside Accumulation and Biomass Production

• Published in: Annals of botany 2000-09, Vol.86 (3), p.527-537
• Main Authors: Hofmann, Rainer W., Swinny, Ewald E., Bloor, Stephen J., Markham, Kenneth R., Ryan, Ken G., Campbell, Bruce D., Jordan, Brian R., Fountain, David W.
• Format: Article
• Language: English
• Subjects: biomass; flavonoids; Flavonols; genetic variation; HPLC; intraspecific; kaempferol; NMR; quercetin; Trifolium repens; Ultraviolet-B; Ultraviolet-B, Trifolium repens, white clover, HPLC, NMR, flavonoids, flavonols, quercetin, kaempferol, biomass, genetic variation, intraspecific; white clover
• ISSN: 0305-7364; 1095-8290
• DOI: 10.1006/anbo.2000.1216

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 13.3kJ m−2d−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 by1H and13C 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.