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Plastids are major organelle
Organelle

In cell biology, an organelle is a specialized subunit within a cell that has a specific function, and is usually separately enclosed within its own lipid membrane....
s 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
Biological pigment

Biological pigments, also known simply as pigments or biochromes are substances produced by living organisms that have a color resulting from selective Absorption ....
 used in photosynthesis, and the types of pigments present can change or determine the cell
Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
's color.

Plastids in plants
Plastids are responsible for photosynthesis
Photosynthesis

File:Seawifs global biosphere.jpgPhotosynthesis is a metabolic pathway that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight....
, 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.






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Encyclopedia


Plastids are major organelle
Organelle

In cell biology, an organelle is a specialized subunit within a cell that has a specific function, and is usually separately enclosed within its own lipid membrane....
s 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
Biological pigment

Biological pigments, also known simply as pigments or biochromes are substances produced by living organisms that have a color resulting from selective Absorption ....
 used in photosynthesis, and the types of pigments present can change or determine the cell
Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
's color.

Plastids in plants


Plastids are responsible for photosynthesis
Photosynthesis

File:Seawifs global biosphere.jpgPhotosynthesis is a metabolic pathway that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight....
, 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
Cellular differentiation

In developmental biology, cellular differentiation is the process by which a less specialized cell becomes a more specialized cell type. Differentiation occurs numerous times during the development of a multicellular organism as the organism changes from a single zygote to a complex system of Tissue and cell types....
, or redifferentiate, between these and other forms. All plastids are derived from proplastids (formerly "eoplasts", eo-: dawn, early), which are present in the meristematic
Meristem

A meristem is the biological tissue in all plants consisting of undifferentiated cells and found in zones of the plant where growth can take place....
 regions of the plant. Proplastids and young chloroplasts commonly divide, but more mature chloroplasts also have this capacity.

In plant
Plant

Plants are Life organisms belonging to the Kingdom Plantae. They include familiar organisms such as trees, herbs, bushes, grasses, vines, ferns, mosses, and green algae....
s, plastids may differentiate
Cellular differentiation

In developmental biology, cellular differentiation is the process by which a less specialized cell becomes a more specialized cell type. Differentiation occurs numerous times during the development of a multicellular organism as the organism changes from a single zygote to a complex system of Tissue and cell types....
 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:
  • Chloroplast
    Chloroplast

    Chloroplasts are organelles found in plant cells and other eukaryote organisms that conduct photosynthesis. Chloroplasts capture light energy to conserve Thermodynamic free energy in the form of Adenosine triphosphate and reduce NADP to NADPH through a complex set of processes called photosynthesis....
    s: for photosynthesis
    Photosynthesis

    File:Seawifs global biosphere.jpgPhotosynthesis is a metabolic pathway that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight....
    ; see also etioplast
    Etioplast

    Etioplasts are chloroplasts that have not been exposed to light. They are usually found in plants grown in the dark. If a plant is kept out of light for several days, its normal chloroplasts will actually convert into etioplasts....
    s, the predecessors of chloroplasts
  • Chromoplast
    Chromoplast

    Chromoplasts are plastids responsible for pigment synthesis and storage. They, like all other plastids , are organelles found in specific photosynthetic eukaryotic species....
    s: for pigment synthesis and storage
  • Leucoplast
    Leucoplast

    Leucoplasts are a category of plastid and as such are organelles found in plant cells. They are non-pigmented, in contrast to other plastids such as the chloroplast....
    s: for monoterpene
    Terpene

    Terpenes are a large and varied class of hydrocarbons, produced primarily by a wide variety of plants, particularly conifers, though also by some insects such as termites or swallowtail butterflies, which emit terpenes from their osmeterium....
     synthesis; leucoplasts sometimes differentiate into more specialized plastids:
    • Amyloplast
      Amyloplast

      Amyloplasts are non-pigment organelles found in some plant cells. They are responsible for the synthesis and storage of starch granules, through the polymer of glucose....
      s: for starch
      Starch

      File:Amylose2.svgFile:Amylopektin Sessel.svgStarch or amylum is a polysaccharide carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds....
       storage
      • Statolith
        Statolith

        Statoliths are a specialized form of amyloplasts involved in gravity perception by plants and most invertebrates.These specialized amyloplasts are denser than the cytoplasm and can sediment according to the gravity vector....
        s: for detecting gravity
    • Elaioplast
      Elaioplast

      Elaioplasts are a type of leucoplast which is specialized for the storage of lipids in plants. Elaioplasts house oil body deposits as rounded plastoglobuli, which are essentially fat droplets....
      s: for storing fat
      Fat

      Fats consist of a wide group of compounds that are generally soluble in organic solvents and largely insoluble in water. Chemistry, fats are generally ester of glycerol and fatty acids....
    • Proteinoplast
      Proteinoplast

      Proteinoplasts are specialized organelles found only in plant cells. They contain crystalline bodies of protein and can be the sites of enzyme activity involving those proteins....
      s: for storing and modifying protein
      Protein

      Proteins are organic compounds made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid Residue ....

Each plastid creates multiple copies of the circular 75-250 kilo bases
Base pair

In molecular biology, two nucleotides on opposite complementarity DNA or RNA strands that are connected via hydrogen bonds are called a base pair ....
 plastid genome
Genome

In classical genetics, the genome of a diploid organism including eukarya refers to a full set of chromosomes or genes in a gamete; thereby, a regular somatic cell contains two full sets of genomes....
. The number of genome copies per plastid is flexible, ranging from more than 1000 in rapidly dividing cells
Cell division

Cell division is a process by which a cell , called the parent cell, divides into two or more cells, called daughter cells. Cell division is usually a small segment of a larger cell cycle....
, 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 gene
Gene

A gene is the basic unit of heredity in a living organism. All living things depend on genes. Genes hold the information to build and maintain their cell and pass genetic trait to offspring....
s encoding ribosomal and transfer ribonucleic acids (rRNAs and tRNAs) as well as protein
Protein

Proteins are organic compounds made of amino acids arranged in a linear chain and joined together by peptide bonds between the carboxyl and amino groups of adjacent amino acid Residue ....
s involved in photosynthesis
Photosynthesis

File:Seawifs global biosphere.jpgPhotosynthesis is a metabolic pathway that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight....
 and plastid gene transcription
Transcription (genetics)

Transcription is the synthesis of RNA under the direction of DNA. RNA synthesis, or transcription, is the process of transcribing DNA nucleotide sequence information into RNA sequence information....
 and translation
Translation

Translation is the hermeneutics of the Meaning of a text and the subsequent production of an Dynamic and formal equivalence text, likewise called a "translation," that communicates the same message in another language....
. 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
Cell nucleus

In cell biology, the nucleus , also sometimes referred to as the "control center", is a membrane-enclosed organelle found in all eukaryote cell ....
 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
Inner membrane

The inner membrane is the biological membrane of an organelle or Gram-negative bacteria that is within an outer membrane.In eukaryotic cells, this inner membrane is present within the nuclear envelope, mitochondria and plastids like the chloroplast....
 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 cell
Plant cell

Plant cells are eukaryote cells that differ in several key respects from the cell of other eukaryote organisms. Their distinctive features include:...
s long thin protuberances called stromule
Stromule

Stromules are microscopy structures found in plant cells.Stromules are highly dynamic structures extending from the surface of all plastid types, including proplastids, chloroplasts, etioplasts, leucoplasts, amyloplasts, and chromoplasts....
s sometimes form and extend from the main plastid body into the cytosol
Cytosol

The cytosol or intracellular fluid is the liquid found inside cell . In eukaryotes this liquid is separated by cell membranes from the contents of the organelles suspended in the cytosol, such as the mitochondrial matrix inside the mitochondrion....
 and interconnect several plastids. Proteins, and presumably smaller molecules, can move within stromule
Stromule

Stromules are microscopy structures found in plant cells.Stromules are highly dynamic structures extending from the surface of all plastid types, including proplastids, chloroplasts, etioplasts, leucoplasts, amyloplasts, and chromoplasts....
s. Most cultured cells that are relatively large compared to other plant cells have very long and abundant stromules that extend to the cell periphery.

Plastids in algae


In algae
Algae

Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms. The largest and most complex marine forms are called seaweeds....
, the term leucoplast (leukoplast) is used for all unpigmented plastids. Their function differ from the leukoplasts in plants. Etioplast
Etioplast

Etioplasts are chloroplasts that have not been exposed to light. They are usually found in plants grown in the dark. If a plant is kept out of light for several days, its normal chloroplasts will actually convert into etioplasts....
, amyloplast
Amyloplast

Amyloplasts are non-pigment organelles found in some plant cells. They are responsible for the synthesis and storage of starch granules, through the polymer of glucose....
 and chromoplast
Chromoplast

Chromoplasts are plastids responsible for pigment synthesis and storage. They, like all other plastids , are organelles found in specific photosynthetic eukaryotic species....
 are plant-specific and do not occur in algae. Algal plastids may also differ from plant plastids in that they contain pyrenoid
Pyrenoid

In cell biology, pyrenoids are centers of Carbon fixation within the chloroplasts of algae and hornworts. Pyrenoids are not biological membrane-bound organelles, but specialized areas of the plastid that contain high levels of ribulose-1,5-bisphosphate carboxylase/oxygenase ....
s.

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
Algae

Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms. The largest and most complex marine forms are called seaweeds....
 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
Cyanobacteria

Cyanobacteria, also known as blue-green algae, blue-green bacteria or Cyanophyta, is a phylum of bacteria that obtain their energy through photosynthesis....
. They developed around 1500 mya and allowed eukaryotes to carry out oxygenic photosynthesis. Due to a split-up into three evolutionary lineages, the plastids are named differently: chloroplasts in green algae
Green algae

The green algae are the large group of algae from which the embryophytes emerged. As such, they form a paraphyletic group, although the group including both green algae and embryophytes is monophyletic ....
 and plant
Plant

Plants are Life organisms belonging to the Kingdom Plantae. They include familiar organisms such as trees, herbs, bushes, grasses, vines, ferns, mosses, and green algae....
s, rhodoplasts in red algae and cyanelles in the glaucophyte
Glaucophyte

The glaucophytes, also known as glaucocystophytes or glaucocystids, are a small group of freshwater microscopic algae. Together with the red algae and Viridiplantae they form the Archaeplastida....
s. 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 thylakoid
Thylakoid

A thylakoid is a membrane-bound compartment inside chloroplasts and cyanobacterium. They are the site of the light-dependent reactions of photosynthesis....
s. 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
Eukaryote

Animals, plants, fungus, and protists are eukaryotes , organisms whose Cell are organized into complex structures enclosed within Cell membrane....
 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 heterokont
Heterokont

The heterokonts or stramenopiles are a major line of eukaryotes presently containing about 10,500 known species. Most are algae, ranging from the giant multicellular kelp to the unicellular diatoms, which are a primary component of plankton....
s, haptophyte
Haptophyte

The haptophytes, classed either as the Prymnesiophyta or Haptophyta, are a phylum of algae. The chloroplasts are pigmented similarly to those of the heterokonts, such as golden algae, but the structure of the rest of the cell is different, so it may be that they are a separate line whose chloroplasts are derived from similar endosymbionts....
s, cryptomonads, and most dinoflagellate
Dinoflagellate

The dinoflagellates are a large group of flagellate protists. Most are marine plankton, but they are common in fresh water habitats as well. Their populations are distributed depending on sea surface temperature, salinity, or depth....
s (= rhodoplasts). Those that endosymbiosed a green alga include the euglenid
Euglenid

The euglenids are one of the best-known groups of flagellates, commonly found in freshwater especially when it is rich in organic materials, with a few marine and endosymbiotic members....
s and chlorarachniophyte
Chlorarachniophyte

Chlorarachniophytes are a small group of algae occasionally found in tropical oceans. They are typically mixotrophic, ingesting bacterium and smaller protists as well as conducting photosynthesis....
s (= chloroplasts). The Apicomplexa
Apicomplexa

The Apicomplexa are a large group of protists, characterized by the presence of a unique organelle called an apical complex . They are unicellular, spore-forming, and exclusively parasites of animals....
, a phylum of obligate parasitic protozoa including the causative agents of malaria (Plasmodium
Plasmodium

Plasmodium is a genus of parasitic protozoa. Infection with these parasites is known as malaria. The genus Plasmodium was created in 1885 by Ettore Marchiafava and Angelo Celli....
 spp.), toxoplasmosis
Toxoplasmosis

Toxoplasmosis is a parasitic disease caused by the protozoan Toxoplasma gondii. The parasite infects most genera of warm-blooded animals, including humans, but the primary host is the Felidae....
 (Toxoplasma gondii
Toxoplasma gondii

Toxoplasma gondii is a species of parasite protozoa in the genus Toxoplasma. The definitive host of T. gondii is the cat, but the parasite can be carried by all known mammals....
), 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
Cryptosporidium parvum

'Cryptosporidium parvum' is one of several species that cause cryptosporidiosis, a parasitic disease of the mammalian intestine .Primary symptoms of C....
, which causes cryptosporidiosis
Cryptosporidiosis

Cryptosporidiosis, also known as crypto . , is a parasitic disease caused by Cryptosporidium, a protozoan parasite in the phylum Apicomplexa....
). The 'apicoplast
Apicoplast

The apicoplast is a relict, non-photosynthetic plastid found in most Apicomplexa, including malaria parasites such as Plasmodium falciparum, but not in others such as Cryptosporidium....
' 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
Kleptoplasty

Kleptoplasty or kleptoplastidy is a symbiosis phenomenon whereby plastids from algae are sequestered by host organisms. The alga is eaten normally and partially digested, leaving the plastid intact....
.

Sources


  • : contains fluorescence images of chloroplast
    Chloroplast

    Chloroplasts are organelles found in plant cells and other eukaryote organisms that conduct photosynthesis. Chloroplasts capture light energy to conserve Thermodynamic free energy in the form of Adenosine triphosphate and reduce NADP to NADPH through a complex set of processes called photosynthesis....
    s and stromule
    Stromule

    Stromules are microscopy structures found in plant cells.Stromules are highly dynamic structures extending from the surface of all plastid types, including proplastids, chloroplasts, etioplasts, leucoplasts, amyloplasts, and chromoplasts....
    s as well as an easy to read chapter.


  • Continuous expression in tobacco leaves of a Brassica napus PEND homologue blocks differentiation of plastids and development of palisade cells Wycliffe et al., 2005. The Plant Journal Volume 44 Issue 1 Page 1.


  • Birky, C. W. 2001. The inheritance of genes in mitochondria and chloroplasts: laws, mechanisms and models. Annual Review of Genetics 35: 125-148.


Further reading

  • Bhattacharya, D. (Ed.) 1997 Origins of Algae and their Plastids. Springer-Verlag/Wein, New York. ISBN 3-211-83036-7