Principles of Biochemistry Volume 2 - A. Lehninger 1985

Bioenergetics and Metabolism
Photosynthesis
Thylakoids also contain accessory pigments

Along with chlorophylls, thylakoid membranes also contain several minor light-absorbing pigments known as accessory pigments. These include various carotenoids, which are yellow, red, or purple in color. Among the most important are the red pigment ß-carotene (Fig. 23-9)—an isoprenoid compound that serves as a precursor to vitamin A in animals (Section 10.14)—and the yellow carotenoid xanthophyll. Because carotenoids absorb light in a different wavelength range than chlorophylls, they function as complementary light receptors. The relative Abundance of chlorophylls and various carotenoids varies significantly among plant species. This pigment ratio determines the characteristic coloration of photosynthetic Cells, which ranges from the blue-green of spruce needles or the bright green of maple leaves to the red, brown, or even purple hues seen in various multicellular Algae and the leaves of certain ornamental plants.

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Fig. 23-9. ß-Carotene, an accessory pigment in green leaves. Many other carotenoids serve as accessory pigments in various plant species. Note that the ß-carotene molecule, much like the chlorophyll molecule, contains numerous conjugated double bonds, which enable it to absorb light and transfer excitons.