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{{Short description|Plant cell organelles that perform photosynthesis and store starch}}
[[File:Plagiomnium affine laminazellen.jpeg|thumb|Plant cells with visible [[chloroplasts]]]]

A '''plastid''' is a [[membrane-bound organelle]] found in the [[Cell (biology)|cell]]s of [[plants]], [[algae]], and some other [[eukaryotic]] organisms. Plastids are considered to be intracellular [[endosymbiotic]] [[cyanobacteria]].<ref>{{cite book| vauthors = Sato N |pages= 75–102 |title=The Structure and Function of Plastids|volume=23| veditors = Wise RR, Hoober JK |publisher= Springer Netherlands|chapter=Origin and Evolution of Plastids: Genomic View on the Unification and Diversity of Plastids|isbn=978-1-4020-4060-3|doi=10.1007/978-1-4020-4061-0_4|series=Advances in Photosynthesis and Respiration|date=2007 }}</ref>

Examples of plastids include [[chloroplast]]s (used for [[photosynthesis]]); [[chromoplast]]s (used for synthesis and storage of pigments); [[leucoplast]]s (non-pigmented plastids, some of which can [[cellular differentiation|differentiate]]); and [[apicoplast]]s (non-photosynthetic plastids of [[apicomplexa]] derived from secondary endosymbiosis).

A permanent primary endosymbiosis event occurred about 1.5 billion years ago in the [[Archaeplastida]] clade{{mdash}}[[Embryophyte|land plants]], [[red algae]], [[green algae]] and [[glaucophyte]]s{{mdash}}probably with a [[cyanobiont]], a symbiotic cyanobacteria related to the genus ''[[Gloeomargarita lithophora|Gloeomargarita]]''.<ref>{{cite journal | vauthors = Moore KR, Magnabosco C, Momper L, Gold DA, Bosak T, Fournier GP | title = An Expanded Ribosomal Phylogeny of Cyanobacteria Supports a Deep Placement of Plastids | language = en | journal = Frontiers in Microbiology | volume = 10 | pages = 1612 | date = 2019 | pmid = 31354692 | pmc = 6640209 | doi = 10.3389/fmicb.2019.01612 | doi-access = free }}</ref><ref>{{Cite journal|last1=Vries|first1=Jan de|last2=Gould|first2=Sven B.|date=2018-01-15|title=The monoplastidic bottleneck in algae and plant evolution|url=https://jcs.biologists.org/content/131/2/jcs203414|journal=Journal of Cell Science|language=en|volume=131|issue=2|pages=jcs203414|doi=10.1242/jcs.203414|issn=0021-9533|pmid=28893840|doi-access=free}}</ref> Another primary endosymbiosis event occurred later, between 140 and 90 million years ago, in the photosynthetic plastids ''[[Paulinella]]'' [[amoeboid]]s of the cyanobacteria genera ''[[Prochlorococcus]]'' and ''[[Synechococcus]]'', or the "PS-clade".<ref name="Marin Nowack Glöckner Melkonian 2021 p.">{{cite journal|last1=Marin|first1=Birger|last2=Nowack|first2=Eva CM|last3=Glöckner|first3=Gernot|last4=Melkonian|first4=Michael|date=2007-06-05|title=The ancestor of the Paulinella chromatophore obtained a carboxysomal operon by horizontal gene transfer from a Nitrococcus-like γ-proteobacterium|journal=BMC Evolutionary Biology|volume=7|issue=1 |page=85|doi=10.1186/1471-2148-7-85|pmc=1904183|pmid=17550603|bibcode=2007BMCEE...7...85M |doi-access=free}}</ref><ref name="Ochoa de Alda-2014">{{Cite journal|last1=Ochoa de Alda|first1=Jesús A. G.|last2=Esteban|first2=Rocío|last3=Diago|first3=María Luz|last4=Houmard|first4=Jean|date=2014-01-29|title=The plastid ancestor originated among one of the major cyanobacterial lineages|journal=Nature Communications|language=en|volume=5|issue=1|pages=4937|doi=10.1038/ncomms5937|pmid=25222494|bibcode=2014NatCo...5.4937O|issn=2041-1723|doi-access=free}}</ref> [[Chloroplast#Secondary and tertiary endosymbiosis|Secondary and tertiary endosymbiosis]] events have also occurred in a wide variety of organisms; and some organisms developed the capacity to sequester ingested plastids{{mdash}}a process known as [[kleptoplasty]].

[[Andreas Franz Wilhelm Schimper|A. F. W. Schimper]]<ref>Schimper, A.F.W. (1882) "[https://www.biodiversitylibrary.org/page/55891946 Ueber die Gestalten der Stärkebildner und Farbkörper]" ''Botanisches Centralblatt'' 12(5): 175–178.</ref>{{efn|Sometimes [[Ernst Haeckel]] is credited to coin the term plastid, but his "plastid" includes nucleated cells and anucleated "cytodes"<ref>Haeckel, E. (1866) "[https://www.biodiversitylibrary.org/page/47207027 Morphologische Individuen erster Ordnung: Plastiden oder Plasmastücke]" in his ''Generelle Morphologie der Organismen'' Bd. 1, pp. 269–289</ref> and thus totally different concept from the plastid in modern literature.}} was the first to name, describe, and provide a clear definition of plastids, which possess a [[DNA#Base pairing|double-stranded DNA]] molecule that long has been thought of as circular in shape, like that of the [[circular prokaryote chromosome|circular chromosome]] of [[prokaryotic cells|''pro''karyotic cells]]{{mdash}}but now, perhaps not; (see [[chloroplast DNA#Molecular structure|"..a linear shape"]]). Plastids are sites for manufacturing and storing pigments and other important chemical compounds used by the cells of [[autotroph]]ic [[eukaryote]]s. Some contain [[biological pigments]] such as used in [[photosynthesis]] or which determine a cell's color. Plastids in organisms that have lost their photosynthetic properties are highly useful for manufacturing molecules like the [[Terpenoid|isoprenoids]].<ref>[https://www.the-scientist.com/news-opinion/picozoans-are-algae-after-all-study-68741 Picozoans Are Algae After All: Study | The Scientist Magazine®]</ref>

== In land plants ==
[[Image:Plastids types.svg|right|300px|thumb|Plastid types]]
[[File:010-Sol-tub-40xHF-Gewebe.jpg|300px|thumbnail|right|[[Leucoplast]]s in plant cells.]]

===Chloroplasts, proplastids, and differentiation===
In [[Embryophyte|land plants]], the plastids that contain [[chlorophyll]] can perform [[photosynthesis]], thereby creating internal chemical energy from external [[light energy|sunlight energy]] while capturing carbon from Earth's atmosphere and furnishing the atmosphere with life-giving oxygen. These are the ''chlorophyll-plastids''{{mdash}}and they are named [[chloroplasts]]; (see top graphic).

Other plastids can synthesize [[fatty acids]] and [[terpenes]], which may be used to produce energy or as raw material to synthesize other molecules. For example, plastid [[epidermal cells]] manufacture the components of the tissue system known as [[plant cuticle]], including its [[epicuticular wax]], from [[palmitic acid]]{{mdash}}which itself is synthesized in the chloroplasts of the [[mesophyll tissue]]. Plastids function to store different components including [[starch]]es, [[fat]]s, and [[protein]]s.<ref name=Kolattukudy>Kolattukudy, P.E. (1996) "Biosynthetic pathways of cutin and waxes, and their sensitivity to environmental stresses", pp. 83–108 in: ''Plant Cuticles''. G. Kerstiens (ed.), BIOS Scientific publishers Ltd., Oxford</ref>

All plastids are derived from proplastids (also named proplasts<ref name="proplast">{{cite journal|vauthors=Azevedo J, Courtois F, Hakimi MA, Demarsy E, Lagrange T, Alcaraz JP, Jaiswal P, Maréchal-Drouard L, Lerbs-Mache S|title=Intraplastidial trafficking of a phage-type RNA polymerase is mediated by a thylakoid RING-H2 protein|journal=Proc Natl Acad Sci U S A|date=2008-07-01|volume=105|issue=26|pages=9123–9128|doi=10.1073/pnas.0800909105|pmid=18567673|pmc=2449375}}</ref>), which are present in the [[meristem]]atic regions of the plant. Proplastids and young chloroplasts typically divide by [[binary fission]], but more mature chloroplasts also have this capacity.

Plant ''proplastids'' (undifferentiated plastids) may [[cellular differentiation|differentiate]] into several forms, depending upon which function they perform in the cell, (see top graphic). They may develop into any of the following variants:<ref name=wise>{{cite book |last=Wise |first=Robert R. |title=The Structure and Function of Plastids |chapter=The Diversity of Plastid Form and Function |series=Advances in Photosynthesis and Respiration |publisher=Springer |date=2006 |volume=23 |pages=3–26 |doi=10.1007/978-1-4020-4061-0_1 |isbn=978-1-4020-4060-3 }}</ref>
* [[Chloroplast]]s: typically green plastids that perform [[photosynthesis]]. 
** [[Etioplast]]s: precursors of chloroplasts.
* [[Chromoplast]]s: coloured plastids that synthesize and store pigments.
* [[Gerontoplast]]s: plastids that control the dismantling of the photosynthetic apparatus during [[plant senescence]].
* [[Leucoplast]]s: colourless plastids that synthesize [[terpene|monoterpene]]s.
Leucoplasts differentiate into even more specialized plastids, such as:
* the [[leucoplasts#Background|aleuroplasts]];
** [[Amyloplast]]s: storing [[starch]] and detecting [[gravity]]{{mdash}}for maintaining [[Gravitropism#Gravity-sensing mechanisms|geotropism]].
** [[Elaioplast]]s: storing [[fat]]s.
** [[Proteinoplast]]s: storing and modifying [[protein]].
* or [[Tannosome]]s: synthesizing and producing [[tannin]]s and [[polyphenols]].

Depending on their morphology and target function, plastids have the ability to differentiate or redifferentiate between these and other forms.

===Plastomes and Chloroplast DNA/ RNA; plastid DNA and plastid nucleoids===

Each plastid creates multiple copies of its own unique genome, or [[plastome]], (from 'plastid genome'){{mdash}}which for a chlorophyll plastid (or chloroplast) is equivalent to a 'chloroplast genome', or a 'chloroplast DNA'.<ref>{{cite journal |last1=Wicke |first1=S |last2=Schneeweiss |first2=GM |last3=dePamphilis |first3=CW |last4=Müller |first4=KF |last5=Quandt |first5=D |title=The evolution of the plastid chromosome in land plants: gene content, gene order, gene function |journal=Plant Molecular Biology |date=2011 |volume=76 |issue=3–5 |pages=273–297 |doi=10.1007/s11103-011-9762-4 |pmid=21424877 |pmc=3104136 |doi-access=free |bibcode=2011PMolB..76..273W }}</ref><ref>{{cite journal |last1=Wicke |first1=S |last2=Naumann |first2=J |title=Molecular evolution of plastid genomes in parasitic flowering plants |journal=Advances in Botanical Research |date=2018 |volume=85 |pages=315–347 |doi=10.1016/bs.abr.2017.11.014 |isbn=9780128134573 |url=https://www.sciencedirect.com/science/article/pii/S0065229617300861|url-access=subscription }}</ref> The number of genome copies produced per plastid is variable, ranging from 1000 or more in [[cell division|rapidly dividing new cells]], encompassing only a few plastids, down to 100 or less in mature cells, encompassing numerous plastids.

A plastome typically contains a [[genome]] that encodes ''transfer'' [[ribonucleic acid]]s ([[tRNA]])s and ''ribosomal'' [[ribonucleic acid]]s ([[rRNA]]s). It also contains proteins involved in photosynthesis and plastid gene [[Transcription (genetics)|transcription]] and [[Translation (biology)|translation]]. But these proteins represent only a small fraction of the total protein set-up necessary to build and maintain any particular type of plastid. [[Cell nucleus|Nuclear]] genes (in the cell nucleus of a plant) encode the vast majority of plastid proteins; and the expression of nuclear and plastid genes is co-regulated to coordinate the development and [[cell differentiation|differention]] of plastids.

Many plastids, particularly those responsible for photosynthesis, possess numerous internal membrane layers. Plastid DNA exists as protein-DNA complexes associated as localized ''regions'' within the plastid's inner envelope [[Inner nuclear membrane|membrane]]; and these complexes are called 'plastid [[nucleoid]]s'. Unlike the nucleus of a eukaryotic cell, a plastid nucleoid is ''not'' surrounded by a nuclear membrane. The region of each nucleoid may contain more than 10 copies of the plastid DNA.

Where the proplastid (''undifferentiated plastid'') contains a single nucleoid region located near the centre of the proplastid, the ''developing (or differentiating) plastid'' has many nucleoids localized at the periphery of the plastid and bound to the inner envelope membrane. During the development/ differentiation of proplastids to chloroplasts{{mdash}}and when plastids are differentiating from one type to another{{mdash}}nucleoids change in morphology, size, and location within the organelle. The remodelling of plastid nucleoids is believed to occur by modifications to the abundance of and the composition of nucleoid proteins.

In normal [[plant cell]]s long thin protuberances called [[stromule]]s sometimes form{{mdash}}extending from the plastid body into the cell [[cytosol]] while interconnecting several plastids. Proteins and smaller molecules can move around and through the stromules. Comparatively, in the laboratory, most cultured cells{{mdash}}which are large compared to normal plant cells{{mdash}}produce very long and abundant stromules that extend to the cell periphery.

In 2014, evidence was found of the possible loss of plastid genome in ''[[Rafflesia]] lagascae'', a non-photosynthetic [[Parasitism|parasitic]] flowering plant, and in ''[[Polytomella]]'', a genus of non-photosynthetic [[green algae]]. Extensive searches for plastid genes in both [[taxon]]s yielded no results, but concluding that their plastomes are entirely missing is still disputed.<ref name="The Scientist">{{Cite web|title = Plants Without Plastid Genomes|url = https://www.the-scientist.com/plants-without-plastid-genomes-37895|website = The Scientist|access-date = 2015-09-26}}</ref> Some scientists argue that plastid genome loss is unlikely since even these non-photosynthetic plastids contain genes necessary to complete various [[Biosynthesis|biosynthetic pathways]] including heme biosynthesis.<ref name="The Scientist" /><ref>{{cite journal | vauthors = Barbrook AC, Howe CJ, Purton S | title = Why are plastid genomes retained in non-photosynthetic organisms? | journal = Trends in Plant Science | volume = 11 | issue = 2 | pages = 101–8 | date = February 2006 | pmid = 16406301 | doi = 10.1016/j.tplants.2005.12.004 }}</ref>

Even with any loss of plastid genome in [[Rafflesiaceae]], the plastids still occur there as "shells" without DNA content,<ref name="NoDNA">{{cite web|title =DNA of Giant 'Corpse Flower' Parasite Surprises Biologists|url=https://www.quantamagazine.org/dna-of-giant-corpse-flower-parasite-surprises-biologists-20210421/| date =April 2021}}</ref> which is reminiscent of [[hydrogenosome]]s in various organisms.

==In algae and protists==
Plastid types in [[algae]] and [[protist]]s include:

* [[Chloroplast]]s: found in [[green algae]] (plants) and other organisms that derived their genomes from green algae.
* [[Glaucophyte#muroplast|Muroplasts]]: also known as cyanoplasts or cyanelles, the plastids of [[glaucophyte]] algae are similar to plant chloroplasts, excepting they have a [[peptidoglycan]] [[cell wall]] that is similar to that of [[bacteria]].
* [[Red algae#Chloroplasts|Rhodoplasts]]: the red plastids found in [[red algae]], which allows them to photosynthesize down to marine depths of 268 m.<ref name=wise/> The chloroplasts of plants differ from rhodoplasts in their ability to synthesize starch, which is stored in the form of granules within the plastids. In red algae, [[floridean starch]] is synthesized and stored outside the plastids in the cytosol.<ref name=Viola>{{cite journal | vauthors = Viola R, Nyvall P, Pedersén M | title = The unique features of starch metabolism in red algae | journal = Proceedings. Biological Sciences | volume = 268 | issue = 1474 | pages = 1417–22 | date = July 2001 | pmid = 11429143 | pmc = 1088757 | doi = 10.1098/rspb.2001.1644 }}</ref>
* [[Chloroplast#Secondary and tertiary endosymbiosis|Secondary and tertiary plastids]]: from endosymbiosis of [[green algae]] and [[red algae]].
* [[Leucoplast]]: in [[algae]], the term is used for all unpigmented plastids. Their function differs from the leucoplasts of plants.
* [[Apicoplast]]: the non-photosynthetic plastids of [[Apicomplexa]] derived from secondary endosymbiosis.

The plastid of photosynthetic ''[[Paulinella]]'' species is often referred to as the 'cyanelle' or chromatophore, and is used in photosynthesis.<ref name="Nature 2019">{{cite journal | title=Evolutionary dynamics of the chromatophore genome in three photosynthetic Paulinella species - Scientific Reports | journal=Scientific Reports | date=2019-02-22 | volume=9 | issue=1 | page=2560 | doi=10.1038/s41598-019-38621-8 | last1=Lhee | first1=Duckhyun | last2=Ha | first2=Ji-San | last3=Kim | first3=Sunju | last4=Park | first4=Myung Gil | last5=Bhattacharya | first5=Debashish | last6=Yoon | first6=Hwan Su | pmid=30796245 | pmc=6384880 | bibcode=2019NatSR...9.2560L }}</ref><ref name="Gabr Grossman Bhattacharya pp. 837–843">{{cite journal | last1=Gabr | first1=Arwa | last2=Grossman | first2=Arthur R. | last3=Bhattacharya | first3=Debashish | editor-last=Palenik | editor-first=B. | title=Paulinella , a model for understanding plastid primary endosymbiosis | journal=Journal of Phycology | publisher=Wiley | volume=56 | issue=4 | date=2020-05-05 | issn=0022-3646 | doi=10.1111/jpy.13003 | pages=837–843| pmid=32289879 | pmc=7734844 | bibcode=2020JPcgy..56..837G }}</ref> It had a much more recent endosymbiotic event, in the range of 140–90 million years ago, which is the only other known primary endosymbiosis event of cyanobacteria.<ref>{{Cite journal|last1=Sánchez-Baracaldo|first1=Patricia|last2=Raven|first2=John A.|last3=Pisani|first3=Davide|last4=Knoll|first4=Andrew H.|date=2017-09-12|title=Early photosynthetic eukaryotes inhabited low-salinity habitats|journal=Proceedings of the National Academy of Sciences|language=en|volume=114|issue=37|pages=E7737–E7745|doi=10.1073/pnas.1620089114|issn=0027-8424|pmc=5603991|pmid=28808007|bibcode=2017PNAS..114E7737S |doi-access=free}}</ref><ref>{{cite Q|Q36374426|pmc=4866557|doi-access=free}}</ref>

[[Etioplast]]s, [[amyloplast]]s and [[chromoplast]]s are plant-specific and do not occur in algae.{{Citation needed|date=February 2010}} Plastids in algae and [[hornwort]]s may also differ from plant plastids in that they contain [[pyrenoid]]s.<ref>{{cite journal | vauthors=((Robison, T. A.)), ((Oh, Z. G.)), ((Lafferty, D.)), ((Xu, X.)), ((Villarreal, J. C. A.)), ((Gunn, L. H.)), ((Li, F.-W.)) | journal=Nature Plants | title=Hornworts reveal a spatial model for pyrenoid-based CO2-concentrating mechanisms in land plants | pages=63–73 | publisher=Nature Publishing Group | date=3 January 2025 | volume=11 | issue=1 | issn=2055-0278 | doi=10.1038/s41477-024-01871-0| pmid=39753956 }}
</ref>

==Inheritance==
In reproducing, most plants inherit their plastids from only one parent. In general, [[angiosperms]] inherit plastids from the female [[gamete]], where many [[gymnosperms]] inherit plastids from the male [[pollen]]. Algae also inherit plastids from just one parent. Thus the plastid DNA of the other parent is completely lost.

In normal intraspecific crossings{{mdash}}resulting in normal hybrids of one species{{mdash}}the inheriting of plastid DNA appears to be strictly uniparental; i.e., from the female. In interspecific hybridisations, however, the inheriting is apparently more erratic. Although plastids are inherited mainly from the female in interspecific hybridisations, there are many reports of hybrids of flowering plants producing plastids from the male.
Approximately 20% of angiosperms, including [[alfalfa]] (''Medicago sativa''), normally show biparental inheriting of plastids.<ref>{{cite journal | vauthors = Zhang Q | title = Why does biparental plastid inheritance revive in angiosperms? | journal = Journal of Plant Research | volume = 123 | issue = 2 | pages = 201–6 | date = March 2010 | pmid = 20052516 | doi = 10.1007/s10265-009-0291-z | bibcode = 2010JPlR..123..201Z | s2cid = 5108244 }}</ref>

==DNA damage and repair==

The plastid [[DNA]] of [[maize]] seedlings is subjected to increasing damage as the seedlings develop.<ref name="pmid25261192">{{cite journal | vauthors = Kumar RA, Oldenburg DJ, Bendich AJ | title = Changes in DNA damage, molecular integrity, and copy number for plastid DNA and mitochondrial DNA during maize development | journal = Journal of Experimental Botany | volume = 65 | issue = 22 | pages = 6425–39 | date = December 2014 | pmid = 25261192 | pmc = 4246179 | doi = 10.1093/jxb/eru359 }}</ref> The DNA damage is due to oxidative environments created by [[photo-oxidation of polymers|photo-oxidative reactions]] and [[photosynthesis|photosynthetic]]/ [[electron transport chain|respiratory electron transfer]]. Some DNA molecules are [[DNA repair|repaired]] but DNA with unrepaired damage is apparently degraded to non-functional fragments.

[[DNA repair]] proteins are encoded by the cell's [[nuclear genome]] and then translocated to plastids where they maintain [[genome]] stability/ integrity by repairing the plastid's DNA.<ref name="pmid26579143">{{cite journal | vauthors = Oldenburg DJ, Bendich AJ | title = DNA maintenance in plastids and mitochondria of plants | journal = Frontiers in Plant Science | volume = 6 | pages = 883 | date = 2015 | pmid = 26579143 | pmc = 4624840 | doi = 10.3389/fpls.2015.00883 | doi-access = free | bibcode = 2015FrPS....6..883O }}</ref> For example, in [[chloroplast]]s of the moss ''[[Physcomitrella patens]]'', a protein employed in DNA mismatch repair (Msh1) interacts with proteins employed in recombinational repair ([[RecA]] and RecG) to maintain plastid genome stability.<ref name="pmid28407383">{{cite journal | vauthors = Odahara M, Kishita Y, Sekine Y | title = MSH1 maintains organelle genome stability and genetically interacts with RECA and RECG in the moss Physcomitrella patens | journal = The Plant Journal | volume = 91 | issue = 3 | pages = 455–465 | date = August 2017 | pmid = 28407383 | doi = 10.1111/tpj.13573 | doi-access = free | bibcode = 2017PlJ....91..455O }}</ref>

==Origin==
Plastids are thought to be descended from [[endosymbiosis|endosymbiotic]] [[cyanobacteria]]. The primary endosymbiotic event of the Archaeplastida is hypothesized to have occurred around 1.5 billion years ago<ref>{{cite journal | vauthors = Ochoa de Alda JA, Esteban R, Diago ML, Houmard J | title = The plastid ancestor originated among one of the major cyanobacterial lineages | journal = Nature Communications | volume = 5 | pages = 4937 | date = September 2014 | pmid = 25222494 | doi = 10.1038/ncomms5937 | bibcode = 2014NatCo...5.4937O | doi-access = free }}</ref> and enabled eukaryotes to carry out [[Carbon fixation#Oxygenic photosynthesis|oxygenic photosynthesis]].<ref>{{cite journal | vauthors = Hedges SB, Blair JE, Venturi ML, Shoe JL | title = A molecular timescale of eukaryote evolution and the rise of complex multicellular life | journal = BMC Evolutionary Biology | volume = 4 | pages = 2 | date = January 2004 | pmid = 15005799 | pmc = 341452 | doi = 10.1186/1471-2148-4-2 | doi-access = free }}</ref> Three evolutionary lineages in the Archaeplastida have since emerged in which the plastids are named differently: chloroplasts in [[green algae]] and/or plants, [[rhodoplast]]s in [[red algae]], and [[muroplast]]s in the glaucophytes. The plastids differ both in their pigmentation and in their ultrastructure. For example, chloroplasts in plants and green algae have lost all [[phycobilisomes]], the [[light harvesting complex]]es found in cyanobacteria, red algae and glaucophytes, but instead contain [[Stroma (fluid)|stroma]] and grana [[thylakoid]]s. The glaucocystophycean plastid—in contrast to chloroplasts and rhodoplasts—is still surrounded by the remains of the cyanobacterial cell wall. All these primary plastids are surrounded by two membranes.

The plastid of photosynthetic ''[[Paulinella]]'' species is often referred to as the 'cyanelle' or chromatophore, and had a much more recent endosymbiotic event about 90–140 million years ago; it is the only known primary endosymbiosis event of cyanobacteria outside of the Archaeplastida.<ref name="Nature 2019"/><ref name="Gabr Grossman Bhattacharya pp. 837–843"/> The plastid belongs to the "PS-clade" (of the cyanobacteria genera ''[[Prochlorococcus]]'' and ''[[Synechococcus]]''), which is a different sister clade to the plastids belonging to the Archaeplastida.<ref name="Marin Nowack Glöckner Melkonian 2021 p. "/><ref name="Ochoa de Alda-2014" />

In contrast to primary plastids derived from primary endosymbiosis of a prokaryoctyic cyanobacteria, complex plastids originated by secondary [[endosymbiosis]] in which a eukaryotic organism engulfed another eukaryotic organism that contained a primary plastid.<ref>{{Cite journal|title = The Origin of Plastids |url = http://www.nature.com/scitable/topicpage/the-origin-of-plastids-14125758|journal=Nature Education|page=84|volume=3|issue=9|year=2010| vauthors = Chan CX, Bhattachary D }}</ref> When a [[eukaryote]] engulfs a red or a green alga and retains the algal plastid, that plastid 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]]s, [[haptophyte]]s, [[cryptomonads]], and most [[dinoflagellate]]s (= rhodoplasts). Those that endosymbiosed a green alga include the [[euglenid]]s and [[chlorarachniophyte]]s (= chloroplasts). The [[Apicomplexa]], a phylum of [[Obligate parasite|obligate parasitic]] [[alveolates]] 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 [[drug target|target]] for [[antiparasitic drug]] development.

Some [[dinoflagellates]] and [[sea slug]]s, in particular of the genus ''[[Elysia (gastropod)|Elysia]]'', 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. This process is known as [[kleptoplasty]], from the Greek, ''kleptes'' ({{wikt-lang|grc|κλέπτης}}), thief.

== Plastid development cycle ==
[[File:Plastid development cycle .jpg|thumb|208x208px|An illustration of the stages of inter-conversion in plastids]]
In 1977 J.M Whatley proposed a plastid development cycle which said that plastid development is not always unidirectional but is instead a complicated cyclic process. Proplastids are the precursor of the more differentiated forms of plastids, as shown in the diagram to the right.<ref>{{Cite journal|last=Whatley|first=Jean M.|date=1978|title=A Suggested Cycle of Plastid Developmental Interrelationships|journal=The New Phytologist|volume=80|issue=3|pages=489–502|doi=10.1111/j.1469-8137.1978.tb01581.x|jstor=2431207|issn=0028-646X|doi-access=free|bibcode=1978NewPh..80..489W }}</ref>

== See also ==
* {{annotated link|Mitochondrion}}
* {{annotated link|Cytoskeleton}}
* {{annotated link|Photosymbiosis}}

== Notes ==
{{Notelist}}

== References ==
{{Reflist|30em}}

== Further reading ==
{{Refbegin}}
* {{cite web | first1 = Maureen R. | last1 = Hanson | first2 = Rainer H. | last2 = Köhler | name-list-style = vanc | url = http://www.plantphys.net/article.php?ch=e&id=122 | archive-url = https://web.archive.org/web/20050614082020/http://www.plantphys.net/article.php?ch=e&id=122 | url-status = dead | archive-date = 2005-06-14 | title = A Novel View of Chloroplast Structure | work = Plant Physiology Online }}
* {{cite journal | vauthors = Wycliffe P, Sitbon F, Wernersson J, Ezcurra I, Ellerström M, Rask L | title = Continuous expression in tobacco leaves of a Brassica napus PEND homologue blocks differentiation of plastids and development of palisade cells | journal = The Plant Journal | volume = 44 | issue = 1 | pages = 1–15 | date = October 2005 | pmid = 16167891 | doi = 10.1111/j.1365-313X.2005.02482.x | doi-access = free }}
* {{cite journal | vauthors = Birky CW | title = The inheritance of genes in mitochondria and chloroplasts: laws, mechanisms, and models | journal = Annual Review of Genetics | volume = 35 | pages = 125–48 | year = 2001 | pmid = 11700280 | doi = 10.1146/annurev.genet.35.102401.090231 | url = http://www.hos.ufl.edu/ctdcweb/Birky01.pdf | access-date = 2009-03-01 | archive-url = https://web.archive.org/web/20100622141202/http://www.hos.ufl.edu/ctdcweb/Birky01.pdf | archive-date = 2010-06-22 | url-status = dead }}
* {{cite journal |vauthors=Chan CX, Bhattacharya D |title=The origins of plastids |journal=Nature Education |volume=3 |issue=9 |pages=84 |year=2010 |url=http://www.nature.com/scitable/topicpage/the-origin-of-plastids-14125758}}
* {{cite book | veditors = Bhattacharya D |title=Origins of Algae and their Plastids |publisher=Springer-Verlag/Wein |location=New York |year=1997 |isbn=978-3-211-83036-9 }}
* {{cite journal | vauthors = Gould SB, Waller RF, McFadden GI | title = Plastid evolution | journal = Annual Review of Plant Biology | volume = 59 | pages = 491–517 | date = 2008 | issue = 1 | pmid = 18315522 | doi = 10.1146/annurev.arplant.59.032607.092915 | bibcode = 2008AnRPB..59..491G | s2cid = 30458113 }}
* {{cite journal | vauthors = Keeling PJ | title = The endosymbiotic origin, diversification and fate of plastids | journal = Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences | volume = 365 | issue = 1541 | pages = 729–48 | date = March 2010 | pmid = 20124341 | pmc = 2817223 | doi = 10.1098/rstb.2009.0103 }}
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== External links ==
*[https://web.archive.org/web/20110720155136/http://www.coextra.eu/projects/project199.html Transplastomic plants for biocontainment (biological confinement of transgenes)] — Co-extra research project on coexistence and traceability of GM and non-GM supply chains
* [http://tolweb.org/Eukaryotes/3 Tree of Life Eukaryotes]

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{{organelles}}
{{Botany}}
{{Self-replicating organic structures}}
{{Organisms et al.}}
{{Authority control}}

[[Category:Organelles]]
[[Category:Plant physiology]]
[[Category:Photosynthesis]]
[[Category:Endosymbiotic events]]