Plastids

media type="youtube" key="KNT2HxzfAzE" height="344" width="425" __Chromoplasts in a red pepper__

Chromoplast Chromoplasts are plastids responsible for pigment synthesis and storage. They, like all other plastids including chloroplasts and leucoplasts, are organelles found in specific photosynthetic eukaryotic species. Chromoplasts in the traditional sense, are found in coloured organs of plants such as fruit and floral petals, to which they give 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 tomato fruit is a classic example. Chromoplasts synthesize and store pigments such as orange carotenes, yellow xanthophylls and various other red pigments; as such, their color varies depending on what pigment they contain. The probable main evolutionary role of chromoplasts is to act as an attractant for pollinating animals e.g. insects or for seed dispersal via the eating of colored fruits. They allow the accumulation of large quantities of water-insoluble compounds in otherwise watery parts of plants. In chloroplasts, some carotenoids are also used as accessory pigments in photosynthesis, where they act to increase the efficiency of chlorophyll in harvesting light energy. When leaves change color in autumn, it is due to the loss of green chlorophyll unmasking these carotenoids that are already present in the leaf. In this case, relatively little new carotenoids are produced. Therefore, the change in plastid pigments associated with leaf senescence is somewhat different from the active conversion to chromoplasts observed in fruit and flowers.

__Plastids in plants__ Plastids are responsible for photosynthesis, storage of products like starch and for the synthesis of many classes of molecules such as fatty acids and terpenes which are needed as cellular building blocks and/or for the function of the plant. Depending on their morphology and function, plastids have the ability to differentiate, or redifferentiate, between these and other forms. All plastids are derived from proplastids (formerly "eoplasts", eo-: dawn, early), which are present in the meristematic regions of the plant. Proplastids and young chloroplasts commonly divide, but more mature chloroplasts also have this capacity.

Plastids
http://www.ibiblio.org/virtualcell/textbook/chapter3/cyto3d.htm
 * [[image:http://www.ibiblio.org/virtualcell/textbook/chapter3/movies/cyto8.gif width="200" height="200"]] || Plastids are large organelles found on plants and some protists but not in animals or fungi. They can easily be seem through a light microscope. Chloroplasts represent one group of plastids called chromoplasts (colored plastids). The otherclass of plastid are called leucoplasts (colorless plastids); they usually store food molecules. Included in this group are amyloplasts or starch plastids shown here in potato root cell. ||



In plants, plastids may differentiate into several forms, depending upon which function they need to play in the cell. Undifferentiated plastids (proplastids) may develop into any of the following plastids:

Chloroplasts: for photosynthesis; see also etioplasts, the predecessors of chloroplasts Chromoplasts: for pigment synthesis and storage Leucoplasts: for monoterpene synthesis; leucoplasts sometimes differentiate into more specialized plastids: Amyloplasts: for starch storage Statoliths: for detecting gravity Elaioplasts: for storing fat Proteinoplasts: for storing and modifying protein

Each plastid creates multiple copies of the circular 75-250 kilo bases plastid genome. The number of genome copies per plastid is flexible, ranging from more than 1000 in rapidly dividing cells, which generally contain few plastids, to 100 or fewer in mature cells, where plastid divisions has given rise to a large number of plastids. The plastid genome contains about 100 genes encoding ribosomal and transfer ribonucleic acids (rRNAs and tRNAs) as well as proteins involved in photosynthesis and plastid gene transcription and translation. However, these proteins only represent a small fraction of the total protein set-up necessary to build and maintain the structure and function of a particular type of plastid. Nuclear genes encode the vast majority of plastid proteins, and the expression of plastid genes and nuclear genes is tightly co-regulated to allow proper development of plastids in relation to cell differentiation.

Plastid DNA exists as large protein-DNA complexes associated with the inner envelope membrane and called 'plastid nucleoids'. Each nucleoid particle may contain more than 10 copies of the plastid DNA. The proplastid contains a single nucleoid located in the centre of the plastid. The developing plastid has many nucleoids, localized at the periphery of the plastid, bound to the inner envelope membrane. During the development of proplastids to chloroplasts, and when plastids convert from one type to another, nucleoids change in morphology, size and location within the organelle. The remodelling of nucleoids is believed to occur by modifications to the composition and abundance of nucleoid proteins.

Many plastids, particularly those responsible for photosynthesis, possess numerous internal membrane layers.

In plant cells long thin protuberances called stromules sometimes form and extend from the main plastid body into the cytosol and interconnect several plastids. Proteins, and presumably smaller molecules, can move within stromules. Most cultured cells that are relatively large compared to other plant cells have very long and abundant stromules that extend to the cell periphery. by lack of light. They contain a dark crystalline bodies, called prolamellar body , which is essentially a cluster of thylakoid membranes in a somewhat tubular form. ** LEUCOPLAST ** types: non-pigmented plastids... [[|figure]] amyloplasts - colorless plant organelle related to starch production & storage aleuroplasts - colorless plant organelle related to protein production & storage elaioplats - colorless plant organelle related to oil & lipid production & storage **CHROMOPLASTS** - often red, yellow or orange in color; they are found in petals of flowers and in fruit. their color is due to two pigments, carotene and xanthophyll. Function - primary function in the cells of flowers is to attract agents of pollination, and in fruit to attract agents of dispersal. http://porpax.bio.miami.edu/~cmallery/150/cells/plastid.htm
 * ETIOPLAST ** - plastid whose development into a chloroplast has been arrested (stopped)

 Plastids are cells that store specific things.  They are large cytoplasmic organelles found in the cells of most plants, but they are not found not in animal cells..  Plastids form small colorless bodies called proplastids.  Once formed certain kinds of plastids can be converted into other types.  For ex. chlorophyll can be synthesized with a leucoplast and light.  There are three plastid categories- Leucoplasts (white or colorless plastids that store starch granules), Chromoplasts (colored plastids that store pigment molecules) and Chloroplasts which are essential in the photosynthetic process || __Plastids__ http://sln.fi.edu/qa97/biology/cells/cell4.html
 * 
 * Plastids are cells that store specific things.
 * They are large cytoplasmic organelles found in the cells of most plants, but they are not found not in animal cells..
 * Plastids form small colorless bodies called proplastids.
 * Once formed certain kinds of plastids can be converted into other types.
 * For ex. chlorophyll can be synthesized with a leucoplast and light.
 * There are three plastid categories- Leucoplasts (white or colorless plastids that store starch granules), Chromoplasts (colored plastids that store pigment molecules) and Chloroplasts which are essential in the photosynthetic process.

Plastids are organelles which are found only in autotrophic cells. In many respects, plastids are similar to entire prokaryotic organisms; they contain their own DNA and can replicate themselves. Like the mitochondria, plastids have an outer membrane which separates them from the cytoplasm and a highly folded inner membrane. Plastids come in three different types: leucoplasts, chloroplasts, and chromoplasts.

[|Plastids] are responsible for [|photosynthesis], storage of products like starch and for the synthesis of many classes of molecules such as [|fatty acids] and [|terpenes] which are needed as cellular building blocks and/or for the function of the plant. Depending on their morphology and function, plastids have the ability to [|differentiate], or redifferentiate, between these and

other forms. All plastids are derived from [|proplastids] (formerly "eoplasts", //eo//-: dawn, early), which are present in the [|meristematic] regions of the plant. Proplastids and young chloroplasts commonly divide, but more mature chloroplasts also have this capacity.  In [|plants], plastids may [|differentiate] into several forms, depending upon which function they need to play in the cell. Undifferentiated plastids (//proplastids//) may develop into any of the following plastids:
 * [|Chloroplasts]: for [|photosynthesis]; //see also [|etioplasts], the predecessors of chloroplasts//
 * [|Chromoplasts]: for pigment synthesis and storage
 * [|Leucoplasts]: for [|monoterpene] synthesis; //leucoplasts sometimes differentiate into more specialized plastids://
 * [|Amyloplasts]: for [|starch] storage
 * [|Statoliths]: for detecting [|gravity]
 * [|Elaioplasts]: for storing [|fat]
 * [|Proteinoplasts]: for storing and modifying [|protein]

Each plastid creates multiple copies of the circular 75-250 [|kilo bases] plastid [|genome]. The number of genome copies per plastid is flexible, ranging from more than 1000 in rapidly [|dividing cells], which generally contain few plastids, to 100 or fewer in mature cells, where plastid divisions has given rise to a large number of plastids. The plastid genome contains about 100 [|genes] encoding ribosomal and transfer [|ribonucleic acids] ([|rRNAs] and [|tRNAs]) as well as [|proteins] involved in [|photosynthesis] and plastid gene [|transcription] and [|translation]. However, these proteins only represent a small fraction of the total protein set-up necessary to build and maintain the structure and function of a particular type of plastid. [|Nuclear] genes encode the vast majority of plastid proteins, and the expression of plastid genes and nuclear genes is tightly co-regulated to allow proper development of plastids in relation to [|cell differentiation]. Plastid DNA exists as large protein-DNA complexes associated with the inner envelope [|membrane] and called 'plastid nucleoids'. Each nucleoid particle may contain more than 10 copies of the plastid DNA. The proplastid contains a single nucleoid located in the centre of the plastid. The developing plastid has many nucleoids, localized at the periphery of the plastid, bound to the inner envelope membrane. During the development of proplastids to chloroplasts, and when plastids convert from one type to another, nucleoids change in morphology, size and location within the organelle. The remodelling of nucleoids is believed to occur by modifications to the composition and abundance of nucleoid proteins. Many plastids, particularly those responsible for photosynthesis, possess numerous internal membrane layers. In [|plant cells] long thin protuberances called [|stromules] sometimes form and extend from the main plastid body into the [|cytosol] and interconnect several plastids. Proteins, and presumably smaller molecules, can move within [|stromules]. Most cultured cells that are relatively large compared to other plant cells have very long and abundant stromules that extend to the cell periphery.

Chloroplasts are the most familiar plastids. They are usually disk-shaped and about 5-8 µm in diameter and 2-4 µm thick. A typical plant cell has 20-40 of them. Chloroplasts are green because they contain chlorophylls - the pigments that harvest the light used in photosynthesis. Chloroplasts are probably the descendants of cyanobacteria that took up residence in the ancestor of the plants. Plant cells that are not engaged in photosynthesis also have plastids that serve other functions, such as
 * [|Link to page on chloroplast structure.] ||
 * [|Link to Chlorophyll] ||
 * [|Links to Photosynthesis] ||
 * [|Link to discussion of the endosymbiotic origin of chloroplasts.] ||
 * storing starch (when they are called **leucoplasts**) [[|View]]
 * storing the [|carotenoids] that give flowers and fruits their color (when they are called **chromoplasts**).


 * PLASTIDS**

Plastids are organelles which are found only in autotrophic cells. In many respects, plastids are similar to entire prokaryotic organisms; they contain their own DNA and can replicate themselves. Like the mitochondria, plastids have an outer membrane which separates them from the cytoplasm and a highly folded inner membrane. Plastids come in three different types: leucoplasts, chloroplasts, and chromoplasts. http://library.thinkquest.org/27819/ch3_9.shtml

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http://www.mhhe.com/biosci/pae/botany/histology/html/plastids.htm http://www.fs.fed.us/conf/fall/leafchng_nf.htm

Plastids are sub-cellular self-replicating organelles present in all living plant cells, and the exclusive site of many important biological processes, the most fundamental being the photosynthetic fixation of CO2 within chloroplasts, a process which is vital to life on earth. In addition, plastid metabolism is responsible for generating economically important raw materials and commodities such as starches and oils, as well as improving the nutritional status of many crop-derived products [1]. All plastids are enclosed by two membranes, the outer and the inner envelope membrane. The outer membrane represents a barrier to the movement of proteins, whilst the inner membrane is the actual permeability barrier between the cytosol and the plastid stroma and the site of specific transport systems connecting both compartments. Plastids are highly compartmentalized organelles, and certain plastid types (chloroplasts and chromoplasts) have been shown to contain lipoprotein particles termed plastoglobules which act as a lipid store during internal membrane biogenesis [2], and may also be the site for important steps in the tocopherol (vitamin E) biosynthetic pathway [3]. A number of plastid types have also been shown to initiate protrusions from the proplastid surface [4] which may be regulated by the number of plastids per cell. These protrusions, termed stromules (white arrowheads in Image-1), have also been shown to be the site of starch granule formation in non-photosynthetic plastids of wheat endosperm [5]. Many of the primary metabolic pathways are shared within different types of plastids, but perform different functions within them and are usually associated with the localization of the plastid within a specialized tissue/organ. For example, starches made inside non-photosynthetic plastids in developing seeds act as a long-term store for the next generation, whereas starches produced in leaf chloroplasts are strictly temporary carbon stores. by lack of light. They contain a dark crystalline bodies, called prolamellar body , which is essentially a cluster of thylakoid membranes in a somewhat tubular form. ** LEUCOPLAST ** types: non-pigmented plastids... [[|figure]] amyloplasts - colorless plant organelle related to starch production & storage aleuroplasts - colorless plant organelle related to protein production & storage elaioplats - colorless plant organelle related to oil & lipid production & storage **CHROMOPLASTS** - often red, yellow or orange in color; they are found in petals of flowers and in fruit. their color is due to two pigments, carotene and xanthophyll. Function - primary function in the cells of flowers is to attract agents of pollination, and in fruit to attract agents of dispersal. Plastids are an important group of plant cellular organelles and comprise one of the primary features that distinguish plant cells from those of other eukaryotes. Plastids are thought to have arisen as a result of an endosymbiotic event in which an early photosynthetic prokaryote invaded a primitive eukaryotic host (Margulis, 1970; Gray, 1992). Subsequently, plastids have evolved to become essential components for plant cell function. Leucoplasts are colorless plastids which store starch (a carbohydrate), proteins, and lipids. These materials are released from the leucoplast when the cell requires them. Chloroplasts are the organelles in which photosynthesis (see Chapter Four) takes place. Photosynthesis is an important process by which autotrophic cells manufacture their own food. Chloroplasts contain the green pigment chlorophyll (this is why plant leaves are green) which absorbs light to provide the energy necessary to complete photosynthesis
 * ETIOPLAST ** - plastid whose development into a chloroplast has been arrested (stopped)

. (image courtesy of [|Nanoworld]) ||  ||
 * || [[image:http://library.thinkquest.org/27819/media/chloro.gif align="center" caption="A chloroplast"]] ||
 * A chloroplast

Chloroplasts have two membranes: an outer membrane and an inner membrane. A solution called the stroma fills the part of the chloroplast inside of the inner membrane. In this area, there are stacks of flattened vesicles. The stacks themselves are known as grana, and the vesicles are called thylakoids. The thylakoids are where photosynthesis actually occurs. Chromoplasts are very similar to chloroplasts, but they do not contain the green pigment chlorophyll. Instead, they contain other pigments which give color to flowers and to leaves during the fall. These other pigments absorb colors of ligh than chlorophyll

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Plastids in algae
In [|algae], the term leucoplast (leukoplast) is used for all unpigmented plastids. Their function differ from the leukoplasts in plants. [|Etioplast], [|amyloplast] and [|chromoplast] are plant-specific and do not occur in algae. Algal plastids may also differ from plant plastids in that they contain [|pyrenoids]. 

Inheritance of plastids
Most plants inherit the plastids from only one parent. [|Angiosperms] generally inherit plastids from the mother, while many [|gymnosperms] inherit plastids from the father. [|Algae] also inherit plastids from only one parent. The plastid DNA of the other parent is thus completely lost. In normal intraspecific crossings (resulting in normal hybrids of one species), the inheritance of plastid DNA appears to be quite strictly 100% uniparental. In interspecific hybridisations, however, the inheritance of plastids appears to be more erratic. Although plastids inherit mainly maternally in interspecific hybridisations, there are many reports of hybrids of flowering plants that contain plastids of the father. 

Origin of plastids
Plastids are thought to have originated from [|endosymbiotic] [|cyanobacteria]. They developed around 1500 mya and allowed eukaryotes to carry out oxygenic photosynthesis.[|[][|1][|]] Due to a split-up into three evolutionary lineages, the plastids are named differently: chloroplasts in [|green algae] and [|plants], rhodoplasts in [|red algae] and cyanelles in the [|glaucophytes]. The plastids differ by their pigmentation, but also in ultrastructure. The chloroplasts e.g. have lost all [|phycobilisomes], the light harvesting complexes found in cyanobacteria, red algae and glaucophytes, but - only in plants and in closely related green algae - contain stroma and grana [|thylakoids]. The glaucocystophycean plastid - in contrast to the chloroplasts and the rhodoplasts - is still surrounded by the remains of the cyanobacterial cell wall. All these primary plastids are surrounded by two membranes. Complex plastids start by secondary [|endosymbiosis], when a [|eukaryote] engulfs a red or green alga and retains the algal plastid, which is typically surrounded by more than two membranes. In some cases these plastids may be reduced in their metabolic and/or photosynthetic capacity. Algae with complex plastids derived by secondary endosymbiosis of a red alga include the [|heterokonts], [|haptophytes], [|cryptomonads], and most [|dinoflagellates] (= rhodoplasts). Those that endosymbiosed a green alga include the [|euglenids] and [|chlorarachniophytes] (= chloroplasts). The [|Apicomplexa], a phylum of obligate parasitic protozoa including the causative agents of malaria (//[|Plasmodium]// spp.), [|toxoplasmosis] (//[|Toxoplasma gondii]//), and many other human or animal diseases also harbor a complex plastid (although this organelle has been lost in some apicomplexans, such as //[|Cryptosporidium parvum]//, which causes [|cryptosporidiosis]). The '[|apicoplast]' is no longer capable of photosynthesis, but is an essential organelle, and a promising target for antiparasitic drug development. Some [|dinoflagellates] take up algae as food and keep the plastid of the digested alga to profit from the photosynthesis; after a while the plastids are also digested. These captured plastids are known as [|kleptoplastids].
 * Plastids** are major [|organelles] found in plants and algae. Plastids are the site of manufacture and storage of important chemical compounds used by the cell. Plastids often contain [|pigments] used in photosynthesis, and the types of pigments present can change or determine the [|cell]'s color.