Xanthophyll 591756 223299743 2008-07-03T13:30:43Z 91.110.158.172 [[Image:Cryptoxanthin.png|thumb|right|400px|The chemical structure of [[cryptoxanthin]]]] '''Xanthophylls''' (originally '''phylloxanthins''') are yellow [[pigment]]s from the [[carotenoid]] group. Their molecular structure is based on [[carotene]]s; contrary to the carotenes, some hydrogen atoms are substituted by [[hydroxyl]] groups and/or some pairs of hydrogen atoms are substituted by oxygen atoms. They are found in the [[leaves]] of most [[plants]] and are synthesized within the [[plastid]]s. They are involved in [[photosynthesis]] along with [[green]] [[chlorophyll]], which typically covers up the yellow except in [[autumn]], when the chlorophyll is denatured by the cold. In plants, xanthophylls are considered [[accessory pigment]]s, along with [[anthocyanin]]s, [[carotene]]s, and sometimes [[phycobiliprotein]]s. Xanthophylls, along with carotenic pigments are seen when leaves turn orange in the autumn season. [[Animal]]s cannot produce xanthophylls, and thus xanthophylls found in animals (e.g. in the eye) come from their food intake. The yellow color of chicken [[Egg (biology)|egg]] [[yolk]]s also comes from ingested xanthophylls. Xanthophylls are oxidized derivatives of [[carotene]]s. They contain [[hydroxyl group]]s and are more [[polar molecule|polar]] than carotenes; therefore, carotenes travel further than xanthophylls in [[paper chromatography]]. The group of xanthophylls includes [[lutein]], [[zeaxanthin]], [[neoxanthin]], [[violaxanthin]], and α- and β-[[cryptoxanthin]]. Xanthophyll has a chemical formula of C<sub>40</sub>H<sub>56</sub>O<sub>2</sub>. ==Xanthophyll cycle== The xanthophyll cycle involves conversions of pigments from a non-energy-quenching form to energy-quenching forms. This is a way to reduce the absorption cross-section of the light harvesting antenna, and thus to reduce the amount of energy that reaches the photosynthetic reaction centers. Reducing the light harvesting antenna is one of the main ways of protecting against [[photoinhibition]] and changes in the xanthophyll cycling takes place on a time scale of minutes to hours.<ref>Falkowski, P. G. & J. A. Raven, 1997, Aquatic photosynthesis. Blackwell Science, 375 pp</ref> In higher plants there are three carotenoid pigments that are active in the xanthophyll cycle: [[violaxanthin]], [[antheraxanthin]] and zeaxanthin. During light stress violoxanthin is converted to antheraxanthin and zeaxanthin, which functions as photoprotective pigments. This conversion is done by the enzyme violaxanthin de-epoxidase.<ref>Taiz, Lincoln and Eduardo Zeiger. 2006. ''Plant Physiology''. Sunderland, MA: Sinauer Associates, Inc. Publishers, Fourth edition, 764 pp</ref> In [[diatoms]] and [[dinoflagellates]] the xanthophyll cycle consists of the pigment [[diadinoxanthin]], which is transformed into [[diatoxanthin]] (diatoms) or [[dinoxanthin]] (dinoflagellates), at high light. <ref>Jeffrey, S. W. & M. Vesk, 1997. Introduction to marine phytoplankton and their pigment signatures. In Jeffrey, S. W., R. F. C. Mantoura & S. W. Wright (eds.), Phytoplankton pigments in oceanography, pp 37-84. – UNESCO Publishing, Paris. </ref> ==References== <references/> *Demmig-Adams, B & W. W. Adams, 2006. Photoprotection in an ecological context: the remarkable complexity of thermal energy dissipation, New Phytologist, 172: 11–21. ==External links== * {{MeshName|Xanthophylls}} {{Plant Pigments}} {{Carotenoids}} [[Category:Carotenoids]] [[ar:كزانتوفيل]] [[cs:Xanthofyly]] [[da:Xantofyl]] [[de:Xanthophylle]] [[et:Ksantofüll]] [[es:Xantófila]] [[eo:Ksantofilo]] [[fr:Xanthophylle]] [[it:Xantofille]] [[mk:Ксантофил]] [[nl:Xantofyl]] [[ja:キサントフィルサイクル]] [[pl:Ksantofile]] [[pt:Xantofila]] [[sv:Xantofyll]]