A substance in a plant that imparts coloration. The photosynthetic pigments are involved in light harvesting and energy transfer in photosynthesis. This group of pigments comprises the tetrapyrroles, which include chlorophylls (chl) and phycobilins, and the carotenoids. The light-absorbing groups of these molecules, the chromophores, contain conjugated double bonds (alternating single and double bonds), which make them effective photoreceptors. The sum of the absorption spectra of the chlorphylls and the carotenoids, evident in the absorption spectrum of a green leaf, is equivalent to the action spectrum of photosynthesis. See also Carotenoid; Chlorophyll;
The second major group comprises the anthocyanins, intensely colored plant pigments responsible for most scarlet, crimson, purple, mauve, and blue colors in higher plants. About 100 different anthocyanins are known. Unlike the chlorophylls and carotenoids, which are lipid-soluble chloroplast pigments, the anthocyanins are water-soluble and are located in the cell vacuole. Chemically, they are a class of flavonoids and are particularly closely related, both structurally and biosynthetically, to the flavonols. Their value to the plant lies in the contrasting colors they provide in flower and fruit, against the green background of the leaf, to attract insects and animals for purposes of pollination and seed dispersal. See also Flavonoid.
