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'[[Image:Ophrys apifera flower1.jpg|thumb|upright|The coloration of the petals and sepals on the [[Ophrys apifera|Bee orchid]] is controlled by a specialized organelle in plant cells called a chromoplast.]] '''Chromoplasts''' are [[plastid]]s, [[heterogeneous]] [[organelles]] responsible for [[pigment]] '''synthesis and storage''' in specific photosynthetic [[eukaryote]]s.<ref name="Whatley_1987">{{cite journal |vauthors=Whatley JM, Whatley FR |title=When is a Chromoplast |journal=New Phytologist |volume=106 |issue=4 |pages=667–678 |year=1987 |doi=10.1111/j.1469-8137.1987.tb00167.x }}</ref> It is [[endosymbiotic theory|thought]] that like all other plastids including [[chloroplast]]s and [[leucoplast]]s they are descended from [[symbiosis|symbiotic]] [[prokaryotes]].<ref name="Camara_1995"/> ==Function== Chromoplasts are found in [[fruits]], [[flowers]], [[root]]s, and stressed and aging [[leaves]], and are responsible for their distinctive colors. This is always associated with a massive increase in the accumulation of [[carotenoid]] pigments. The conversion of [[chloroplasts]] to chromoplasts in [[ripening]] is a classic example. They are generally found in mature tissues and are derived from preexisting mature plastids. Fruits and flowers are the most common structures for the biosynthesis of carotenoids, although other reactions occur there as well including the synthesis of sugars, starches, lipids, aromatic compounds, vitamins and hormones.<ref name="Egea_2010"/> The DNA in chloroplasts and chromoplasts is identical.<ref name="Camara_1995"/> One subtle difference in DNA was found after a liquid chromatography analysis of tomato chromoplasts was conducted, revealing increased [[cytosine methylation]].<ref name="Egea_2010"/> Chromoplasts synthesize and store pigments such as orange [[carotene]], yellow [[xanthophyll]]s, and various other red pigments. As such, their color varies depending on what pigment they contain. The main evolutionary purpose of chromoplasts is probably to attract [[pollinators]] or eaters of colored fruits, which help [[disperse seeds]]. However, they are also found in roots such as [[carrots]] and [[sweet potatoes]]. They allow the accumulation of large quantities of water-insoluble compounds in otherwise watery parts of plants. When [[leaves]] change color in the autumn, it is due to the loss of green [[chlorophyll]], which unmasks preexisting carotenoids. In this case, relatively little new carotenoid is produced—the change in [[plastid]] pigments associated with leaf [[senescence]] is somewhat different from the active conversion to chromoplasts observed in fruit and flowers. There are some species of flowering plants that contain little to no carotenoids. In such cases there are plastids present within the petals that closely resemble chromoplasts and are sometimes visually indistinguishable. [[Anthocyanins]] and [[flavonoids]] located in the cell vacuoles are responsible for other colors of pigment.<ref name="Whatley_1987"/> The term "chromoplast" is occasionally used to include ''any'' plastid that has pigment, mostly to emphasize the difference between them and the various types of [[leucoplast]]s, plastids that have no pigments. In this sense, [[chloroplast]]s are a specific type of chromoplast. Still, "chromoplast" is more often used to denote plastids with pigments other than chlorophyll. ==Structure and classification== Using a [[light microscope]] chromoplasts can be differentiated and are classified into four main types. The first type is composed of proteic [[Stroma (fluid)|stroma]] with granules. The second is composed of protein crystals and [[amorphous]] pigment granules. The third type is composed of protein and pigment crystals. The fourth type is a chromoplast which only contains crystals. An electron microscope reveals even more, allowing for the identification of substructures such as globules, crystals, membranes, [[fibrils]] and [[tubules]]. The substructures found in chromoplasts are not found in the mature [[plastid]] that it divided from.<ref name="Camara_1995">{{cite book |vauthors=Camara B, Hugueney P, Bouvier F, Kuntz M, Monéger R |title=Biochemistry and molecular biology of chromoplast development |journal=Int. Rev. Cytol. |volume=163 |issue= |pages=175–247 |year=1995 |pmid=8522420 |doi=10.1016/s0074-7696(08)62211-1|series=International Review of Cytology |isbn=9780123645678 }}</ref> The presence, frequency and identification of substructures using an electron microscope has led to further classification, dividing chromoplasts into five main categories: Globular chromoplasts, crystalline chromoplasts, fibrillar chromoplasts, tubular chromoplasts and membranous chromoplasts.<ref name="Camara_1995"/> It has also been found that different types of chromoplasts can coexist in the same organ.<ref name="Egea_2010"/> Some examples of plants in the various categories include [[mangoes]], which have globular chromoplasts, and [[carrots]] which have crystalline chromoplasts.<ref name="Atkins_2006">{{cite journal |vauthors=Vasquez-Caicedo AL, Heller A, Neidhart S, Carle R |title=Chromoplast morphology and β-carotene accumulation during postharvest ripening of Mango Cv. 'Tommy Atkins' |journal=J. Agric. Food Chem. |volume=54 |issue=16 |pages=5769–76 |date=August 2006 |pmid=16881676 |doi=10.1021/jf060747u }}</ref> Although some chromoplasts are easily categorized, others have characteristics from multiple categories that make them hard to place. [[Tomato]]es accumulate carotenoids, mainly [[lycopene crystalloids]] in membrane-shaped structures, which could place them in either the crystalline or membranous category.<ref name="Egea_2010"/> ==Evolution== [[Plastids]] are descendants of [[cyanobacteria]], photosynthetic [[prokaryotes]], which integrated themselves into the eukaryotic ancestor of [[algae]] and [[plants]], forming an [[endosymbiotic]] relationship. The ancestors of plastids diversified into a variety of plastid types, including chromoplasts.<ref name="Egea_2010">{{cite journal |vauthors=Egea I, Barsan C, Bian W |title=Chromoplast differentiation: current status and perspectives |journal=Plant Cell Physiol. |volume=51 |issue=10 |pages=1601–11 |date=October 2010 |pmid=20801922 |doi=10.1093/pcp/pcq136 |url=http://pcp.oxfordjournals.org/cgi/pmidlookup?view=long&pmid=20801922|display-authors=etal}}</ref> Plastids also possess their own small genome and some have the ability to produce a percentage of their own proteins. The main evolutionary purpose of chromoplasts is to attract animals and insects to [[pollinate]] their [[flowers]] and disperse their [[seeds]]. The bright colors often produced by chromoplasts is one of many ways to achieve this. Many plants have evolved [[symbiotic]] relationships with a single pollinator. Color can be a very important factor in determining which pollinators visit a flower, as specific colors attract specific pollinators. White flowers tend to attract [[beetles]], [[bees]] are most often attracted to violet and blue flowers, and [[butterflies]] are often attracted to warmer colors like yellows and oranges.<ref name="Waser_1996">{{cite journal |author=Waser, NM. |author2=Chittka, L. |author3=Price, MV. |author4=Williams, NM. |author5=Ollerton, J. |title=Generalization in Pollination Systems, and Why it Matters |journal=Ecology |volume=77 |issue=4 |pages=1043–60 |date=June 1996 |doi=10.2307/2265575 |jstor=2265575 }}</ref> ==Research== Chromoplasts are not widely studied and are rarely the main focus of scientific research. They often play a role in research on the tomato plant (''[[Solanum lycopersicum]]''). [[Lycopene]] is responsible for the red color of a ripe fruit in the cultivated [[tomato]], while the yellow color of the flowers is due to [[xanthophylls]] [[violaxanthin]] and [[neoxanthin]].<ref name="Galpaz_2006">{{cite journal |vauthors=Galpaz N, Ronen G, Khalfa Z, Zamir D, Hirschberg J |title=A chromoplast-specific carotenoid biosynthesis pathway is revealed by cloning of the tomato white-flower locus |journal=Plant Cell |volume=18 |issue=8 |pages=1947–60 |date=August 2006 |pmid=16816137 |pmc=1533990 |doi=10.1105/tpc.105.039966 |url=http://www.plantcell.org/cgi/pmidlookup?view=long&pmid=16816137}}</ref> Carotenoid biosynthesis occurs in both chromoplasts and [[chloroplasts]]. In the chromoplasts of tomato flowers, carotenoid synthesis is regulated by the genes Psyl, Pds, Lcy-b, and Cyc-b. These genes, in addition to others, are responsible for the formation of carotenoids in organs and structures. For example, the Lcy-e gene is highly expressed in [[leaves]], which results in the production of the carotenoid lutein.<ref name="Galpaz_2006"/> White flowers are caused by a recessive [[allele]] in tomato plants. They are less desirable in cultivated crops because they have a lower pollination rate. In one study, it was found that chromoplasts are still present in white flowers. The lack of yellow pigment in their petals and anthers is due to a mutation in the CrtR-b2 gene which disrupts the carotenoid biosynthesis pathway.<ref name="Galpaz_2006"/> <!-- Deleted image removed: [[Image:F2.large.jpg|thumb|right|upright|The photo depicts the transformation of a chloroplast into a chromoplast.]] --> The entire process of chromoplast formation is not yet completely understood on the molecular level. However, electron microscopy has revealed part of the transformation from chloroplast to chromoplast. The transformation starts with remodeling of the internal membrane system with the [[lysis]] of the intergranal [[thylakoids]] and the [[Thylakoid|grana]]. New membrane systems form in organized membrane complexes called [[thylakoid plexus]]. The new membranes are the site of the formation of carotenoid crystals. These newly synthesized membranes do not come from the thylakoids, but rather from vesicles generated from the inner membrane of the plastid. The most obvious biochemical change would be the downregulation of photosynthetic gene expression which results in the loss of [[chlorophyll]] and stops [[photosynthetic]] activity.<ref name="Egea_2010"/> In [[Orange (fruit)|oranges]], the synthesis of carotenoids and the disappearance of chlorophyll causes the color of the fruit to change from green to yellow. The orange color is often added artificially—light yellow-orange is the natural color created by the actual chromoplasts.<ref name="Thomson_1966">{{cite journal |author=Thomson, WW |title=Ultrastructural Development of Chromoplasts in Valencia Oranges |journal=Botanical Gazette |volume=127 |issue=2–3 |pages=133–9 |year=1966 |jstor=2472950 |doi=10.1086/336354}}</ref> Valencia oranges ''[[Citris sinensis L]]'' are a cultivated orange grown extensively in the state of Florida. In the winter, Valencia oranges reach their optimum orange-rind color while reverting to a green color in the spring and summer. While it was originally thought that chromoplasts were the final stage of plastid development, in 1966 it was proved that chromoplasts can revert to chloroplasts, which causes the oranges to turn back to green.<ref name="Thomson_1966"/> ==Compare== [[Image:Plastids types.svg|right|220px]] *[[Plastid]] **[[Chloroplast]] and [[etioplast]] **Chromoplast **[[Leucoplast]] ***[[Amyloplast]] ***[[Elaioplast]] ***[[Proteinoplast]] {{clear}} ==References== {{Reflist}} ==External links== * http://www.daviddarling.info/encyclopedia/C/chromoplast.html * http://www.thefreedictionary.com/chromoplasts {{Organelles}} [[Category:Organelles]]'