SEASONAL DIFFERENCES IN FOLIAR CONTENT OF CHLOROGENIC ACID, A PHENYLPROPANOID ANTIOXIDANT, IN MAHONIA REPENS

To assess the possible physiological function of chlorogenic acid (CGA , 3-O-caffeoylquinic acid) in vivo, we characterized the free radical scavenging properties of pure phenylpropanoids and leaf extracts again st two free radicals, superoxide and the 2,2'-azinobis(3-ethylbenzothi azoline-6-sulphonic acid) (ABTS) radical cation, CGA was found to be a highly efficient scavenger of these free radicals, surpassing the act ivity of all other phenylpropanoids tested, as well as the 'classical' antioxidant ascorbate. Seasonal differences in the leaf content of CG A were examined in field populations of the broadleaf evergreen Mahoni a repens growing in different light environments. Leaves of fully sun- exposed plants contained significantly more (74 +/- 10 mmol m(-2)) CGA in winter than leaves from plants growing under deeply shaded conditi ons (17 +/- 2 mmol m(-2)). Sun-acclimated, but not shade-acclimated, l eaves also produced high levels of anthocyanins in winter, suggesting a simultaneous increase in carbon flow through the phenylpropanoid and flavonoid pathways in response to high light and seasonal low tempera ture stress. In summer, high light-acclimated leaves contained approxi mate to 2-fold less CGA than in winter, whereas CGA levels were simila r between seasons in shaded leaves. Consistent with the strong scaveng ing capacity of CGA measured in vitro, a linear correlation was observ ed between CGA content and the antioxidant activity of leaf extracts i n both scavenging assays. On the basis of these results, we propose th at CGA is a powerful hydrogen-donating antioxidant that may play an im portant role in mitigating the effects of oxidative stress in plants.