The ecophysiology of foliar anthocyanin

The accumulation of foliar anthocyanins can be consistently attributed to a small range of contexts. Foliar anthocyanin accumulates in young, expanding foliage, in autumnal foliage of deciduous species, in response to nutrient deficiency or ultraviolet (UV) radiation exposure, and in association with damage or defense against browsing herbivores or pathogenic fungal infection. A common thread through these causative factors is low photosynthetic capacity of foliage with accumulated anthocyanin relative to leaves at different ontogenetic stages or unaffected by the environmental factor in question. The ecophysiological function of anthocyanin has been hypothesized as: 1) a compatible solute contributing to osmotic adjustment to drought and frost stress; 2) an antioxidant; 3) a UV protectant; and 4) protection from visible light. Review of the internal leaf distribution of anthocyanin, of experimental evidence using seedlings, and of studies that directly investigated light absorption by anthocyanin and its development relative to recognized processes of photoprotection support the hypothesis that anthocyanins provide protection from visible light.