News Release Date: Oct. 18, 2005 Release No. 15-05 Maples gamble on antioxidant’s value, says New England researcher DURHAM, N.H.--Some of foliage season’s most brilliant red leaves each year are more than mere window dressing; they contain some of nature’s more powerful antioxidants. That is the word from USDA Forest Service Researcher Paul Schaberg, a plant physiologist who studies cells, leaves and trees for a living. Schaberg has studied tree health and function in northern New England forests for the past 16years. In the process he has become an expert on the science behind fall’s annual fireworks displays. He said the maples of northern New England are of particular interest. Of all of fall’s brilliant, colorful displays, maple trees exhibit a unique variety of colors that can include the fieriest reds, he said. That is one reason, he said, why he likes to work out of the service’s research facility in Vermont: the area has more maples than just about anywhere else in North America. There’s no doubt that red leaves are an important part of the mosaic of color that drives the estimated one billion dollar fall foliage tourist business in states like Vermont. However, what is less certain is why leaves that are about to fall off of trees would make new red pigments – a process that uses valuable nutrients and energy. Pigments are the chemicals in leaves that produce the colors we see. Some of these pigments are a natural component of summer leaves that help them safely capture the energy from sunlight to produce food such as sugars. Pigments like chlorophylls appear green and carotenoids appear yellow. In the fall, leaves lose their green color as chlorophyll breaks down as a result of normal light and temperature cues like the first frost. This loss of green reveals the yellow pigments that are always there but are usually hidden by the green. However, in some kinds of trees, like the beautiful maples of New England, another change in pigments occurs – red anthocyanins are produced. Red pigments do a number of things that help leaves survive stress. They function as antifreeze by protecting leaves during a frost. They work like a sunscreen by protecting leaves from excess sunlight damage when green pigments fade away. But the most interesting possibility is that they may benefit leaves by acting as antioxidants. Anthocyanins are powerful antioxidants found in healthy foods like red grapes and blueberries, said Schaberg. In fact, anthocyanins are about four times more potent than other antioxidants like vitamin C or E. “There are different types of antioxidants, but they all do the same basic job of reducing the uncontrolled electron transfer that causes oxidative damage,” he said. “There are a lot of different oxidative processes that are good – like part of photosynthesis where the energy of sunlight is harnessed by chlorophyll to produce sugars. This is an example of good oxidation because the controlled transfer of electrons is put to good use.” Schaberg described the uncontrolled oxidation in plants. “In the fall when there is little chlorophyll, sunlight still hits leaves, but instead of doing productive work the electrons run ‘willy nilly’ throughout the leaf, causing oxidative damage. That’s what oxidative stress is: the uncontrolled distribution of electrons damaging tissues. Antioxidants prevent and repair that kind of damage. This protection may be an important reason why red pigments exist in leaves – they protect leaves and let them function long enough to unload nutrients and sugars back into the tree. We believe that promoting this transfer could give trees with red leaves a “head start,” giving them extra nutrition and energy for the next growing season.” “There’s a big difference between maple trees in the amount of anthocyanins they produce. Red maple, when it turns color, has predominantly red leaves. Sugar maples are a lot more variable in the percentage of red leaves. For these trees it isn’t set in stone what color leaves are going to turn in the fall. Stress exposure and the genes of the tree likely influence how much red you see,” he said. “There are all kinds of strategies that trees have to protect themselves and increase their chances of survival. For example, some trees have deep roots to get extra water and survive droughts. Others survive buy just using less of the water they get. Sometimes one strategy works better than another. We think that red leaf coloration may be one of those specialized adaptive traits that some trees use to deal with the stress of leaf loss.” “It’s a gamble for maple trees,” said Schaberg. “They have to use some stored sugars to make anthocyanin that then help leaves survive longer and transport even more sugar back to the tree. Whether this gamble is worth the investment may vary from leaf to leaf, tree to tree and year to year. But whatever the end result is for the tree, one thing is for sure. The end result of nature’s gamble with red pigments always results in a beautiful fall landscape that amazes and delights us leaf peepers”. --END-- |