Contribution of anthocyanins to the antioxidant capacity of juvenile and senescing sugar maple (Acer saccharum) leaves

Foliar anthocyanins are hypothesised to provide an additional source of photoprotection from photooxidative stress to the leaves in which they occur through their ability to scavenge excess free radical species. Although demonstrated to significantly enhance the antioxidant status of red morphs of fully expanded leaves of some species, the contribution of anthocyanins to the antioxidant capacity of the juvenile and senescing leaves in which they frequently occur has not been examined. Antioxidant activity of extracts from anthocyanic and non-anthocyanic juvenile and senescing sugar maple (Acer saccharum Marsh.) leaves from similar light environments was assessed using the stable free radical 1,1-diphenyl-2-picryl hydrazyl (DPPH). Anthocyanin content was significantly correlated with antioxidant activity in extracts of anthocyanic juvenile leaves but only weakly correlated in extracts of anthocyanic senescing leaves. In addition, the antioxidant activity of anthocyanic and non-anthocyanic leaves was equal in both juvenile and senescing leaves. Thus, although anthocyanins may contribute to the antioxidant capacity of anthocyanic juvenile and senescing sugar maple leaves, these results are not consistent with the hypothesis that anthocyanins provide an enhancement to the photoprotection available in either leaf type through free radical scavenging. The results suggest anthocyanins may be part of alternative strategies employed by anthocyanic juvenile and senescing maple leaves to achieve similar levels of antioxidant capacity as their non-anthocyanic counterparts to cope with the same set of environmental challenges.