GOULD, KEVIN S.1*, SAMUEL O. NEILL1, and THOMAS C. VOGELMANN2. 1School of Biological Sciences, University of Auckland, Private Bag 92019, Auckland, New Zealand; 2Department of Botany, University of Wyoming, Laramie WY 82071-3165, USA. - A unified explanation for anthocyanins in leaves?
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