Sc. Grace et al., SEASONAL DIFFERENCES IN FOLIAR CONTENT OF CHLOROGENIC ACID, A PHENYLPROPANOID ANTIOXIDANT, IN MAHONIA REPENS, Plant, cell and environment, 21(5), 1998, pp. 513-521
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.