Accumulation of isoflavonoids in Lotus corniculatus after UV-B irradiation

HPLC profiles of plant defensive compounds, isoflavonoids and flavonoids, were evaluated in the frequently cultivated forage species, Lotus corniculatus, as well as their changes after UV-B irradiation. The predominant flavonoid glycosides are kaempferol 3,7-di-O-rhamnoside together with its malonylated derivative. UV-B irradiation led to a strong increase of vestitol, but the condensed tannin and kaempferol glycosides concentrations were mostly unaffected or tended to decrease. The accumulation of other isoflavonoids, such as sativan or biochanin A was also measured after UV-B treatment. Expression of key enzymes of vestitol and sativan biosynthesis, pterocarpane reductase and isoflavone synthase were strongly stimulated. Therefore, the biosynthesis and accumulation of bioactive isoflavonoid compounds are strongly induced by UV-irradiation.