Anthocyanin is my favorite pigment

In science plants on November 16, 2011 at 12:31 pm

Most people like the color red. We love Dorothy’s ruby red slippers, Snow White’s ruby lips and rosy cheeks. Red apples are delicious. And we thrill to the red color of fall leaves. Brown leaves do not attract. Yellow and orange are nice, but it is a brilliant red leaf that really catches the eye.

The red pigment that we see is anthocyanin. Unlike the orange and yellow pigments, which are related to chlorophyll, anthocyanins usually are not present throughout the year, but are synthesized in response to leaf abscission. The orange and yellow carotenoids are part of the photosynthetic process; they are necessary to help make sugar for the plant to live. Green chlorophyll masks their color. Thus leaves look green until the chlorophyll breaks down during leaf abscission.

Anthocyanins may protect chlorophyll from high light. In an excellent study of dogwood the red leaves occurred higher in the leaf canopy where sun levels were highest. Study authors propose that anthocyanins act as a sunscreen to shield the photosynthetic apparatus from high light. This preserves the proteins and pigments from oxidative destruction. Interestingly, Anthocyanins were concentrated in the upper, or palisade layers of leaves; when leaves were turned over, so that the bottom faced the sun, the anthocyanins formed primarily in the lower or mesophyl layer (plant leaf diagram). This suggests that sunlight induces the formation of the anthocyanins.

Look around and you too may notice that the reddest leaves on a tree are those in the bright sun. Similarly, I see in my Fothergilla, (see above) that the bright red leaves are on a branch most exposed to sunlight, whereas the shade leaves are orange and yellow.

By the way- what’s good for the plant is good for human nutrition too. Foods high in anthocyanins, such as blueberries, also protect our bodies from oxidative damage.

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