Functional role of anthocyanins in high-light winter leaves of the evergreen herb Galax urceolata.

High-light leaves of the evergreen herb Galax urceolata exhibit a striking color change from green to red during winter months due to anthocyanin synthesis in outermost mesophyll cells. Here we investigate three possible functions of this color change. To test the hypothesis that anthocyanins function as light attenuators, maximum photosystem II efficiency (F(v)/F(m)) of red and green leaves was measured during and after exposure to wavelengths either strongly or poorly absorbed by anthocyanin. To determine whether anthocyanins elevate radical-scavenging capacity, antioxidant activity of red and green leaves was assessed using the alpha,alpha-diphenyl-beta-picrylhydrazyl assay. Nonstructural carbohydrate levels were analyzed to test the hypothesis that anthocyanins function as a carbon sink. Declines in F(v)/F(m) under white and green light were significantly greater for green than red leaves, but were comparable under red light. Anthocyanin content positively correlated with antioxidant activity. Although levels of anthocyanins did not appear to be related to nonstructural carbohydrate concentration, high levels of sugars may be necessary for their photo-induction. Results suggest that anthocyanins function as light attenuators and may also contribute to the antioxidant pool in winter leaves.