As I study medicinal plants, one intriguing question keeps cropping up – what is the biological rationale for plants investing in several classes of structurally varied plant secondary metabolites?. Certainly this question drives a number of researchers in the field of plant chemical ecology. Edwards et al (2008) provided some striking evidence from their study of bacteria resistant cotton (Gossypium hirsutum). They detected flavonoid pigments, chrysanthemin and isoquercitin, at unusually high levels in epidermal tissue of young leaves in response to Xanthomonas infection. These cells clustered around infected cells that had died because of the plant’s hypersensitive resistance response. A light activated sesquiterpene, 2,7-dihyroxycadalene, acted as a phytoalexin, destroying both bacteria and plant cell. The presence of the flavanoids in surrounding cells appeared to filter sunlight, limiting the generation of free radicals resulting from light activation of 2,7-dihyroxycadaline. How’s that for compartmentalizing your response to friends and enemies?
Edwards, W.R. (2008) Light filtering by epidermal flavanoids during the resistance response of cotton to Xanthomonas protects leaf tissue from light-dependent phytoalexin toxicity, Phtyochemistry 69:2320-2328.