Hawthorn (Crataegus pinnatifida Bge.) flavonoids constituents have recently received greater attention for their health and medical properties. In order to relgulate the flavonoids constituents, one-year-old hawthorn plants were subjected to foliar application of L-glutamic acid (GLA, 800 mg L–1 ), glycine (GLY, 20 mg L–1), L-phenylalanine (PHE, 20 mg L–1), L-arginine (ARG, 20 mg L–1). The levels of rhamnosylvitexin, rutin and hyperoside in both leaves and root exudates were significantly (p<0.05) increased in GLA and PHE treatments. Application of GLY and PHE increased the levels of rutin and hyperoside in hawthorn roots, especially for PHE treatment, and the level of hyperoside in PHE treatment was significantly (p<0.05) higher than in other treatments. No positive effects were observed for quercetin under exogenous amino acids treatments in both leaves and roots. The total flavonoids content of leaves, roots and root exudates under GLA and PHE treatments were significantly increased compared to the control. In addition, the phenylalanine ammonia-lyase (PAL, EC 188.8.131.52) activities of leaves and roots were also increased. These results suggest that some exogenous amino acids did affect the flavonoids content, which may have significance in regulation of flavonoids in hawthorn.
Key words: Amino acids, flavonoids, phenylalanine ammonia-lyase.