Submitted to: New Phytologist
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/29/2005
Publication Date: 12/1/2005
Citation: Hughes, N.M., Neufeld, H., Burkey, K.O. 2005. Functional role of anthocyanins in high-light winter leaves of the evergreen herb galax urceolata. New Phytologist. 168: 575-587. Interpretive Summary: Two soybean [Glycine max (L.) Merr.] cultivars that exhibit differences in ozone (O3) sensitivity were used to investigate the potential role of leaf extracellular antioxidants in ozone injury responses. Plants were grown in a greenhouse under charcoal-filtered air (CF) conditions to assess genetic and leaf age effects under low stress conditions, or were subjected to CF or O3 treatments in greenhouse exposure chambers to assess O3 effects. In both cultivars, the extracellular ascorbate pool consisted of 80 to 98 percent dehydroascorbic acid (DHA), the oxidized form of ascorbic acid (AA) that does not function as an antioxidant. The predominance of DHA in the apoplast was associated with relatively high ascorbate oxidase and ascorbate peroxidase activities in extracellular extracts from both young and old leaves. For all combinations of genotype and ozone treatment, extracellular AA levels were relatively low (1 to 32 nmol g-1FW) and represented only 3 to 30 percent of the total antioxidant capacity found. However, total extracellular antioxidant capacity was twofold greater in Essex compared with Forrest, which was consistent with lower foliar injury from O3 in Essex. Concentrations of AA and DHA and ascorbate redox status in whole-leaf tissue samples were generally not indicative of differential O3 sensitivity between the cultivars. The results suggest that extracellular antioxidant metabolites in addition to ascorbate contribute to detoxification of O3 in soybean leaves and possibly affect plant sensitivity to O3 injury.
Technical Abstract: High light leaves of the evergreen herb Galax urceolata exhibit a striking color change from green to red during winter months, caused by 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 (Fv/Fm) 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 ','-diphenyl-'-picrylhydrazyl assay. Non-structural carbohydrate levels were analyzed to test the hypothesis that anthocyanins function as a carbon sink. Declines in Fv/Fm under white and green light were significantly greater for green leaves than red, but were comparable under red light. Anthocyanin content positively correlated with antioxidant activity. Although levels of anthocyanins did not appear to be related non-structural carbohydrate concentration, high levels of sugars may be necessary for their photoinduction. Results suggest that anthocyanins function as light-attenuators and may also contribute to the antioxidant pools in winter leaves.