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Q&A
Q. My tree has red leaves all year. How does a plant support itself without green chlorophyll?
A. Some parasitic plants lack chlorophyll entirely and steal the products of photosynthesis from their green hosts, said Susan K. Pell, director of science at the Brooklyn Botanic Garden. Other plants, like a red-leafed tree, have plenty of chlorophyll, but the molecule is masked by another pigment.
Chlorophyll absorbs red and blue light, “reflecting, and thus appearing, green,” Dr. Pell said. Chlorophyll uses this electromagnetic energy, along with carbon dioxide and water, to make glucose and oxygen.
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Most plants also have other pigments: carotenoids, which usually appear yellow to orange, and anthocyanins, which are red to purple. One pigment usually dominates. So a plant with red leaves probably has higher than usual amounts of anthocyanins, Dr. Pell said. But chlorophyll is still present and at work.
“We used to think that all fall foliage color change resulted from the revealing of already-present carotenoids and anthocyanins when chlorophyll was broken down in preparation for dormancy,” she said. We now know that leaves actually produce additional anthocyanins into old age, she said.
The evolutionary advantages are not fully understood, Dr. Pell said. One theory is that extra anthocyanins provide shade under which chloroplasts (structures within cells) can break down their chlorophyll, helping the plant reabsorb its building blocks, especially valuable nitrogen. Another theory is that anthocyanins, which are powerful antioxidants, protect the plants in preparation for winter.
question@nytimes.com
A version of this article appears in print on , Section
D
, Page
4
of the New York edition
with the headline:
Seeing Red. Order Reprints | Today’s Paper | Subscribe
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