<P> Xanthophylls (originally phylloxanthins) are yellow pigments that occur widely in nature and form one of two major divisions of the carotenoid group; the other division is formed by the carotenes . The name is from Greek xanthos (ξανθός, "yellow") and phyllon (φύλλον, "leaf"), due to their formation of the yellow band seen in early chromatography of leaf pigments . </P> <P> The molecular structure of xanthophylls is similar to that of carotenes, but xanthophylls contain oxygen atoms, while carotenes are purely hydrocarbons with no oxygen . Xanthophylls contain their oxygen either as hydroxyl groups and / or as pairs of hydrogen atoms that are substituted by oxygen atoms acting as a bridge (epoxide). For this reason, they are more polar than the purely hydrocarbon carotenes, and it is this difference that allows their separations from carotenes in many types of chromatography . Typically, carotenes are more orange in color than xanthophylls . </P> <P> Like other carotenoids, xanthophylls are found in highest quantity in the leaves of most green plants, where they act to modulate light energy and perhaps serve as a non-photochemical quenching agent to deal with triplet chlorophyll (an excited form of chlorophyll), which is overproduced at high light levels in photosynthesis . The xanthophylls found in the bodies of animals, and in dietary animal products, are ultimately derived from plant sources in the diet . For example, the yellow color of chicken egg yolks, fat, and skin comes from ingested xanthophylls (primarily lutein, which is often added to chicken feed for this purpose). </P> <P> The yellow color of the human macula lutea (literally, yellow spot) in the retina of the eye results from the lutein and zeaxanthin it contains, both xanthophylls again requiring a source in the human diet to be present in the eye . These xanthophylls protect the eye from ionizing blue and ultraviolet light, which they absorb . These two specific xanthophylls do not function in the mechanism of sight, since they cannot be converted to retinal (also called retinaldehyde or vitamin A aldehyde). Their arrangement is believed to be the cause of Haidinger's brush, an entoptic phenomenon that allows the perception of the polarization of light . </P>

Where is xanthophyll found in a plant's cell