The leaves from many of New Zealand's native species are remarkably polymorphic for anthocyanin expression. Red coloration varies not only as a function of seasonal and developmental factors, but can also differ among individuals of a population, among leaves within a canopy, and even among tissues within a leaf. Moreover, the biosynthesis of anthocyanin in these leaves can be induced by a host of disparate environmental and biotic stimuli. Any unified explanation for the presence of anthocyanins in leaves must accommodate both the variability in pigmentation patterns over time and space, and the diverse range of triggers. Our data indicate that anthocyanins confer a phytoprotective role, rather than being the default end-product of a saturated flavonoid metabolism. Anthocyanins are primarily associated with chlorophyllous tissues, and significantly modify both the quantity and quality of light incident on a chloroplast. Red leaves photosynthesise less than green leaves, but are also photoinhibited less and recover sooner following exposure to high light fluxes. Photoabatement also reduces the generation of free radicals and reactive oxygen species from photooxidation, photorespiration, and Mehler reaction activities. Anthocyanins inhibit Fenton hydroxyl radical generation by chelating to ferrous ions, and effectively scavenge superoxide and hydrogen peroxide generated by mechanical injury, sudden temperature changes, and exposures to high light. Anthocyanins are evidently versatile and highly effective phytoprotectants. However, there is probably no unified explanation for their presence in leaves. Common among the first land plants, anthocyanins have probably been hijacked over the course of evolution to perform an array of tasks.

Key words: anthocyanin, antioxidant, free radical, leaf, light, photoinhibition