Why do leaves change color?

For years, scientists have wondered how the leaves prepared for a sprawling performance in autumn. The molecules behind yellow and orange are well understood, but the bright red is still a mystery.

In response to the cold weather and short daytime time, the leaves stopped producing green chlorophyll. This substance helps them absorb light and create energy. Because chlorophyll is sensitive to cold, certain weather conditions such as frost will make the production of this substance turn off faster.

Meanwhile, the yellow and orange pigments called carotenoids , also in carrots, are clearly displayed in the leaf that has been removed in blue.

"The yellow is still there all summer, but you can't see it because it is covered by blue," explains Paul Schaberg, a US Department of Forestry plant physiologist. "In trees like poplar leaves and oak trees, it's a major color change." But scientists know less about the vibrant red colors of maple and ash trees in the fall.

Red comes from anthocyanins, which unlike carotenoids, are only created in the fall. It also brings color to strawberries, red apples and ripe plums.

In trees, these red pigments act as a shield to prevent harmful ultraviolet rays and cover the leaves from being exposed to too much light. It also works to prevent colds, protects cells from freezing and also benefits as antioxidants.

Researchers found that plants produce these substances in response to environmental stresses such as freezing, ultraviolet rays, drought and mold. But red leaves are also a sign of downfall. If you see leaves turning red early, at the end of August, it is possible that the tree has been affected by a fungus or bumped by a network driver.

Why do trees stack energy to create new anthocyanins, while leaves are about to fall off?

"People surmise that it may help the leaves fight against stress , " Schaberg said. "If creating anthocyanins helps the leaves stay on the tree longer, it can help the tree absorb more good things before it falls off. Plants can use these resources for the next growing season."

Scientists hope that understanding anthocyanins will help to better understand plant stress levels and take measures to protect the environment.

MT