Pigments | Research & Encyclopedia Articles

Plant pigments are essential for photosynthesis, a process that supports all plant and animal life. They also play a key role in sensing light to regulate plant development and in establishing the communication between plants and the animals around them. Further, some plant pigments are the source of nutritional compounds required for or useful to the diets of humans and other animals.

The major classes of visible plant pigments are chlorophylls, carotenoids, flavonoids (including anthocyanins), and betalains. Each of these classes of pigments is composed of several individual compounds. For example, there are two major chlorophylls in higher plants, while there are hundreds of carotenoids and flavonoids that occur in nature. Phytochrome is a blue-green plant pigment that is not plentiful enough to be visible but serves as an important sensor of light, which stimulates plant growth and development.

All plants contain chlorophylls and carotenoids in their leaves and other green plant parts. The chlorophylls are green and central to the process of photosynthesis. They capture light energy and convert it to chemical energy to be used not only by plants but by all animals.

The carotenoids and related xanthophylls are red, orange, or yellow and occur in green plant tissues along with chlorophylls in plastids, where they capture oxidizing compounds generated during photosynthesis. Without the protection they offer, photosynthesis cannot occur, so all photosynthetictissue contains both the visible green chlorophylls as well as the masked orange carotenoids. Carotenoids serve another function as accessory light-harvesting pigments and photoreceptors that make photosyn-thesis more efficient.

Animals rely on plant carotenoids as their ultimate source of all vitamin A. Some of the carotenoids, including beta-carotene, possess a chemical structure that allows them to be converted to vitamin A by animals that consume them. Some animals also derive their pigmentation from carotenoids. For example, pink flamingoes and yellow goldfish obtain their colors from dietary carotenoids.

Anthocyanins and other flavonoids, betalains, and some carotenoids serve a key role in attracting the attention of animals for pollination, dissemination of fruit, seed, and storage organs, or warning of undesirable plant flavor or antinutritional compounds. These pigments provide visual cues to animals, alerting them to maturing plant organs without chlorophyll on the background sea of green leaves, stems, and immature flowers and fruit. Anthocyanins in red roses, grapes, and potatoes; betalains in beets; and carotenoids in daylilies, oranges, and carrots are some familiar examples.

The flavonoids include the red and blue anthocyanins that attract the human and higher-animal eye. Other flavonoids are the yellow and white flavonols, flavones, aurones, and chalcones. Some of these are brilliantly colored to insects, which can detect light absorbed in the near ultraviolet range. Tannins are complex flavonoids that contribute to the brown or black color of leaves, seeds, bark, and wood. The betalains are red and yellow pigments that occur in several families of higher plants and serve a function similar to that of anthocyanins.

Anthocyanins; Carotenoids; Chlorophyll; Flavonoids; Phytochrome.

Goodwin, T. W., ed. Chemistry and Biochemistry of Plant Pigments, 2nd ed. New York:Academic Press, 1976.

Gross, Jeana. Pigments in Fruits. London: Academic Press, 1987.

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