(Host) The red color in autumn leaves has not been masked by green chlorophyll; leaves have to make it specially. Ruth Page describes recent discoveries of the ways in which this boosts plant health.
(Page) We know why many tree leaves turn golden in autumn. The yellow color was there all along, and when the chlorophyll disappears as days shorten, the yellow appears.
Why do some plants, especially many of our gorgeous maples, turn scarlet? We know it’s caused by anthocyanins in the leaves, but those were NOT there all summer masked by chlorophyll. The plant has to make them – why waste energy on that, just when they’re trying to close down for winter?
Lots of experiments have been done recently to try to answer this question. We know that anthocyanins in dark fruits like blueberries, and red foods including tomatoes, are healthy for people. They contain antioxidants; oxidation marks the interaction of oxygen with other materials and can be damaging. It’s what rusts iron. Antioxidants we consume will scarf up free radicals that can damage proteins and DNA. Experimenters found that anthocyanins can manage free radicals in a test tube four times as well as the much-touted vitamins C and E. But do they have value to plants?
To get the answer, Science News reports that patient students had to use an imaging technique, impressively called “epi-fluorescence microscopy”; they borrowed it from research with animal cells. They found some plants that make hydrogen peroxide when they’re damaged, for instance by a stab from an aphid. They learned that when they stuck certain leaves with a very fine needle, imitating aphid damage, hydrogen peroxide appeared in the cells. Cells quickly turned red, causing the hydrogen peroxide to disappear fast. But when they stuck needles into green leaves, it took as much as ten minutes for the damaging hydrogen peroxide to disappear.
Further studies show that some leaves turn red to protect themselves from “sunburn;” brilliant bursts of sunshine that are too much for chlorophyll to handle, and slow its work. Chlorophyll, with water and sunlight, makes food for green plants.
Another advantage to leaves that turn red is that anthocyanins regulate the movement of water. Plants want to build up as much strength as possible before the cold of winter. Leaves turn red in response to drought, salt buildup and heat, as they try to protect themselves by hoarding as much water as possible. So anthocyanins are as good for plants as for people. Other ideas being tested have to do with whether the anthocyanins protect leaves from heat or cold, possibly both.
So this autumn when I stop to admire the breath-taking beauty of maples and various shrubs that blaze with fiery color, I’ll think a bit about the complicated chemistry of nature. It has evolved over the millennia to serve this planet’s plants and animals, and incidentally gives us a heady experience of magnificent beauty in four-season areas.
This is Ruth Page, reveling in autumn.