NEILL, SAMUEL O.*, KEVIN S. GOULD, PAUL A. KILMARTIN, KENNETH R. MARKHAM, and KEVIN A. MITCHELL. Plant Science Group, School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand. - Antioxidant strategies of red versus green leaves.
Anthocyanin biosynthesis increases under environmental and biotic
stresses in leaves. These same factors stimulate the production of
reactive oxygen species (ROS). We have tested the theory that
anthocyanins protect leaves from ROS, and that red leaves are better
suited to scavenge ROS than are green leaves. Total antioxidant
activities of leaf extracts from red and green morphs of Quintinia
serrata (Escalloniaceae) and Elatostema rugosum
(Urticaceae) were quantified using (i) their abilities to scavenge the
stable DPPH radical, and (ii) cyclic voltammetry. They were also
analysed for their compositions of flavonoids, hydroxycinnamates and
antioxidant enzymes (superoxide dismutase, catalase, and ascorbate
peroxidase). Red morphs of the shade plant, E. rugosum were
more effective at scavenging ROS than the green morphs; with
anthocyanins being the most active phenolic antioxidant tested.
Anthocyanins appear to be synthesised in juvenile leaves to provide
protection until a sufficient pool of enzymic antioxidants can be
created. In contrast, leaves from red and green morphs of the sun
plant Q. serrata had comparable antioxidant activities. Q.
serrata appears to employ other phenolic compounds in addition to
anthocyanin to provide adequate low molecular weight antioxidant
(LMWA) protection; the hydroxycinnamates were found to be the most
Key words: anthocyanins, Elatostema rugosum (Urticaceae), low molecular weight antioxidants (LMWA), phenolic compounds, Quintinia serrata (Escalloniaceae), reactive oxygen species (ROS)