Foliar anthocyanins: A horticultural review

Anthocyanins, betalains, and carotenoids provide nongreen coloration in plants. In addition to adding aesthetic value to ornamental species, plant pigments play important roles in pollination, light harvesting, plant defense, protection against unfavorable environmental conditions, and human health. In leaves, anthocyanins are responsible for most red, burgundy, and purple coloration. In a small number of families, betalains provide red coloration instead of anthocyanins and the occurrence of these two pigment classes is mutually exclusive. Cyanidin glycosides are the most common anthocyanins in vegetative organs. The biosynthesis and regulation of anthocyanins, factors (biotic and abiotic) influencing their accumulation, their putative functions in leaves, and their impact on leaf photosynthesis will be addressed in this chapter. Environmental factors attributed with anthocyanin accumulation include irradiance (both light quality and quantity), UVB radiation, temperature, nutrient deficiency, drought, and high salinity. The major physiological roles attributed to anthocyanins include herbivory defense, photoprotection, free radical scavenging as antioxidants, and regulation of cell osmotic potential (osmoregulation). Red leaves may have lower, equivalent, or higher photosynthetic rates than comparable green leaves, depending upon species and environmental conditions. Foliar anthocyanins localize in epidermal and/or mesophyll cells, and their location may determine their primary function and impact on leaf photosynthetic rate.