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Plant cell
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{{Short description|Type of eukaryotic cell present in green plants}} {{For|the scientific journal|The Plant Cell}} {{pp-vandalism|small=yes}} [[File:Plant cell structure-en.svg|thumb|upright=1.4|Structure of a plant cell]] '''Plant cells''' are the cells present in [[Viridiplantae|green plants]], photosynthetic [[eukaryote]]s of the kingdom [[Plant]]ae. Their distinctive features include primary cell walls containing cellulose, hemicelluloses and pectin, the presence of plastids with the capability to perform photosynthesis and store starch, a large [[vacuole]] that regulates turgor pressure, the absence of [[Flagellum|flagella]] or [[centriole]]s, except in the gametes, and a unique method of cell division involving the formation of a cell plate or [[phragmoplast]] that separates the new daughter cells. ==Characteristics of plant cells== * Plant cells have [[cell wall]]s composed of [[cellulose]], [[hemicellulose]]s, and [[pectin]] and constructed outside the [[cell membrane]]. Their composition contrasts with the cell walls of [[fungus|fungi]], which are made of [[chitin]], of [[bacteria]], which are made of [[peptidoglycan]] and of [[archaea]], which are made of [[pseudopeptidoglycan]]. In many cases [[lignin]] or [[suberin]] are secreted by the [[protoplast]] as secondary wall layers inside the primary cell wall. [[Cutin]] is secreted outside the primary cell wall and into the outer layers of the secondary cell wall of the epidermal cells of leaves, stems and other above-ground organs to form the [[plant cuticle]]. Cell walls perform many essential functions. They provide shape to form the tissue and organs of the plant, and play an important role in intercellular communication and plant-microbe interactions.<ref name=Keegstra>{{cite journal| last=Keegstra |first=K |date=2010 |title=Plant cell walls |journal=Plant Physiology |volume=154 |issue=2 |pages=483β486 |doi=10.1104/pp.110.161240 |pmc=2949028 |pmid=20921169}}</ref> The cell wall is flexible during growth and has small pores called plasmodesmata that allow the exchange of nutrients and [[Plant hormone|hormones]] between cells.<ref>{{Cite book |last1=Lew |first1=Kristi |url=https://books.google.com/books?id=ttyPEAAAQBAJ&pg=PA12 |title=Plant Cells, Third Edition |last2=Fitzpatrick |first2=Brad |date=2021-08-01 |publisher=Infobase Holdings, Inc |isbn=978-1-64693-728-8 |language=en}}</ref> * Many types of plant cells contain a large central [[vacuole]], a water-filled volume enclosed by a membrane known as the [[tonoplast]]<ref name=JRaven>{{Cite journal |first=JA |last=Raven |date=1997 |title=The vacuole: a cost-benefit analysis |journal=Advances in Botanical Research |volume=25 |pages=59β86 |doi=10.1016/S0065-2296(08)60148-2 |isbn=9780120059256 }}</ref> that maintains the cell's [[turgor]], controls movement of [[molecules]] between the [[cytosol]] and [[plant sap|sap]], stores useful material such as [[phosphorus]] and [[nitrogen]]<ref>{{cite journal |last=Raven |first=J.A. |date=1987 |title=The role of vacuoles |volume=106 |issue=3 |pages=357β422 | doi=10.1111/j.1469-8137.1987.tb00149.x |journal=New Phytologist|doi-access= |bibcode=1987NewPh.106..357R }}</ref> and digests waste [[protein]]s and [[organelle]]s. * Specialized cell-to-cell communication pathways known as [[plasmodesmata]],<ref name=Oparka>{{cite journal |last=Oparka |first=KJ |date=1993 |title=Signalling via plasmodesmata-the neglected pathway |journal=Seminars in Cell Biology |volume=4 |issue=2 |pages=131β138 | doi=10.1006/scel.1993.1016|pmid=8318697 }}</ref> occur in the form of pores in the primary cell wall through which the [[plasmalemma]] and [[endoplasmic reticulum]]<ref name=Hepler>{{cite journal |last=Hepler |first=PK |date=1982 |title=Endoplasmic reticulum in the formation of the cell plate and plasmodesmata |journal=Protoplasma |volume=111 |issue=2 |pages=121β133 |doi=10.1007/BF01282070 |s2cid=8650433 }}</ref> of adjacent cells are continuous. * Plant cells contain [[plastid]]s, the most notable being [[chloroplast]]s, which contain the green-colored pigment [[chlorophyll]] that converts the energy of sunlight into chemical energy that the plant uses to make its own food from water and carbon dioxide in the process known as [[photosynthesis]].<ref>{{Cite encyclopedia|editor-first1=James Alan |editor-last1=Bassham |editor-first2=Hans |editor-last2=Lambers |date=2018 |title=Photosynthesis: importance, process, & reactions |encyclopedia=Encyclopedia Britannica |url=https://www.britannica.com/science/photosynthesis |access-date=2018-04-15|language=en }}</ref> Other types of plastids are the [[amyloplast]]s, specialized for [[starch]] storage, [[elaioplast]]s specialized for [[fat]] storage, and [[chromoplast]]s specialized for synthesis and storage of [[pigment]]s. As in [[mitochondria]], which have a genome encoding 37 genes,<ref name=Andersonetal1981>{{cite journal |last1=Anderson |first1=S |last2=Bankier |first2=AT | last3=Barrell |first3=BG |last4=de Bruijn |first4=MH |last5=Coulson |first5=AR |last6=Drouin |first6=J |last7=Eperon |first7=IC |last8=Nierlich |first8=DP |last9=Roe |first9=BA| last10=Sanger |first10=F |last11=Schreier |first11=PH |last12=Smith |first12=AJ |last13=Staden |first13=R |last14=Young |first14=IG |date=1981 |title=Sequence and organization of the human mitochondrial genome |journal=Nature |volume=290 |issue=5806 |pages=4β65 |doi=10.1038/290457a0 |pmid=7219534|bibcode=1981Natur.290..457A |s2cid=4355527 }}</ref> plastids have their own [[genome]]s of about 100β120 unique [[gene]]s<ref name=Lui>{{cite journal |first1=L |last1=Cui |first2=N |last2=Veeraraghavan |first3=A |last3=Richter |first4=K |last4=Wall |first5=RK |last5=Jansen |first6=J |last6=Leebens-Mack |first7=I |last7=Makalowska |first8=CW |last8=dePamphilis |date=2006 |title=ChloroplastDB: the chloroplast genome database |journal=Nucleic Acids Research |volume=34 |issue=90001 |pages=D692-696 |doi=10.1093/nar/gkj055 |pmid=16381961 |pmc=1347418}}</ref> and are interpreted as having arisen as [[prokaryote|prokaryotic]] [[endosymbiont]]s living in the cells of an early [[eukaryote|eukaryotic]] ancestor of the [[embryophyte|land plants]] and [[algae]].<ref name=Margulis>{{cite book |first=L |last=Margulis |author-link=Lynn Margulis |date=1970 |title=Origin of eukaryotic cells |url=https://archive.org/details/originofeukaryot0000marg |url-access=registration |publisher=Yale University Press |location=New Haven |isbn=978-0300013535 }}</ref> * Cell division in land plants and a few groups of algae, notably the [[Charophyta|charophytes]]<ref name=Lewis2004>{{cite journal |last1=Lewis |first1=LA |last2=McCourt |first2=RM |date=2004 |title=Green algae and the origin of land plants |journal=American Journal of Botany |volume=91 |issue=10 |pages=1535β1556 |doi=10.3732/ajb.91.10.1535 |pmid=21652308|bibcode=2004AmJB...91.1535L }}</ref> and the [[Chlorophyta|chlorophyte]] order [[Trentepohliales]],<ref name=LopezBautista>{{cite journal |last1=LΓ³pez-Bautista |first1=JM |last2=Waters |first2=DA |last3=Chapman |first3=RL |date=2003 |title=Phragmoplastin, green algae and the evolution of cytokinesis |journal=International Journal of Systematic and Evolutionary Microbiology |volume=53 |issue=6 |pages=1715β1718 |doi=10.1099/ijs.0.02561-0 |pmid=14657098|doi-access=free }}</ref> takes place by construction of a [[phragmoplast]] as a template for building a [[cell plate]] late in [[cytokinesis]]. * The motile, free-swimming [[sperm]] of [[bryophyte]]s and [[pteridophytes]], [[cycad]]s and ''[[Ginkgo]]'' are the only cells of land plants to have [[flagella]]<ref name=Silflow>{{cite journal |last1=Silflow |first1=CD |last2=Lefebvre |first2=PA |date=2001 |title=Assembly and motility of eukaryotic cilia and flagella. Lessons from ''Chlamydomonas reinhardtii'' |journal=Plant Physiology |volume=127 |issue=4 |pages=1500β1507 |doi=10.1104/pp.010807 |pmid=11743094 |pmc=1540183}}</ref> similar to those in [[Eukaryote#Animal cell|animal cell]]s.<ref name=Manton>{{cite journal |last1=Manton |first1=I |last2=Clarke |first2=B |date=1952 |title=An electron microscope study of the spermatozoid of ''Sphagnum'' |journal=Journal of Experimental Botany |volume=3 |issue=3 |pages=265β275 |doi=10.1093/jxb/3.3.265 }}</ref><ref name=Paolillo>{{cite journal | first=DJ Jr. | last=Paolillo |date=1967 |title=On the structure of the axoneme in flagella of ''Polytrichum juniperinum'' |journal=Transactions of the American Microscopical Society |volume=86 |issue=4 |pages=428β433 |doi=10.2307/3224266|jstor=3224266 }}</ref> The [[conifers]] and [[flowering plant]]s do not have motile sperm and lack both flagella and [[centriole]]s.<ref name="raven">{{cite book |last1=Raven |first1=PH |last2=Evert |first2=RF |last3=Eichhorm |first3=SE |date=1999 |title=Biology of Plants |url=https://archive.org/details/biologyofplants00rave_0 |url-access=registration |edition= 6th |publisher= W.H. Freeman |location=New York |isbn=9780716762843 }}</ref> ==Types of plant cells and tissues== Plant cells differentiate from undifferentiated [[meristem]]atic cells (analogous to the stem cells of animals) to form the major classes of cells and tissues of [[root]]s, [[plant stem|stems]], [[leaf|leaves]], [[flower]]s, and reproductive structures, each of which may be composed of several cell types. ===Parenchyma=== [[Ground tissue#Parenchyma|Parenchyma cells]] are living cells that have functions ranging from storage and support to [[photosynthesis]] ([[mesophyll]] cells) and phloem loading ([[transfer cells]]). Apart from the xylem and phloem in their vascular bundles, leaves are composed mainly of parenchyma cells. Some parenchyma cells, as in the epidermis, are specialized for light penetration and focusing or regulation of [[gas exchange]], but others are among the least specialized cells in plant tissue, and may remain [[totipotent]], capable of dividing to produce new populations of undifferentiated cells, throughout their lives.<ref name=Haberlandt>{{cite journal |first=Haberlandt |last=G. |date=1902 |title=Kulturversuche mit isolierten Pflanzenzellen |journal=Mathematisch-naturwissenschaftliche |publisher=Akademie der Wissenschaften in Wien Sitzungsberichte |volume=111 |issue=1 |pages=69β92 }}</ref> Parenchyma cells have thin, permeable primary walls enabling the transport of small molecules between them, and their cytoplasm is responsible for a wide range of biochemical functions such as [[nectar]] [[secretion]], or the manufacture of [[secondary metabolite|secondary products]] that discourage [[herbivory]]. Parenchyma cells that contain many chloroplasts and are concerned primarily with photosynthesis are called [[chlorenchyma]] cells. Chlorenchyma cells are parenchyma cells involved in photosynthesis. <ref>{{Cite book|last=Mauseth|first=James D.|url=https://www.worldcat.org/oclc/1122454203|title=Botany : An Introduction to Plant Biology|date=2021|isbn=978-1-284-15737-6|edition=Second|location=Burlington, MA|language=English|oclc=1122454203}}</ref> Others, such as the majority of the parenchyma cells in [[potato]] [[tubers]] and the [[seed]] [[cotyledons]] of [[legumes]], have a storage function. === Collenchyma === [[Ground tissue#Collenchyma|Collenchyma cells]] are alive at maturity and have thickened cellulose cell walls.<ref name="Cutter" /> These cells mature from meristem derivatives that initially resemble parenchyma, but differences quickly become apparent. Plastids do not develop, and the secretory apparatus (ER and Golgi) proliferates to secrete additional primary wall. The wall is most commonly thickest at the corners, where three or more cells come in contact, and thinnest where only two cells come in contact, though other arrangements of the wall thickening are possible.<ref name="Cutter" /> [[Pectin]] and [[hemicellulose]] are the dominant constituents of collenchyma cell walls of [[dicotyledon]] [[angiosperm]]s, which may contain as little as 20% of cellulose in ''[[Petasites]]''.<ref name="Roelofsen">{{cite book|last=Roelofsen|first=PA|title=The plant cell wall|date=1959|publisher=GebrΓΌder Borntraeger|location=Berlin|asin=B0007J57W0}}</ref> Collenchyma cells are typically quite elongated, and may divide transversely to give a septate appearance. The role of this cell type is to support the plant in axes still growing in length, and to confer flexibility and tensile strength on tissues. The primary wall lacks lignin that would make it tough and rigid, so this cell type provides what could be called plastic support β support that can hold a young stem or petiole into the air, but in cells that can be stretched as the cells around them elongate. Stretchable support (without elastic snap-back) is a good way to describe what collenchyma does. Parts of the strings in celery are collenchyma. {{Plain image with caption|Plant cell types.svg|Cross section of a leaf showing various plant cell types|550px|right}} ===Sclerenchyma=== [[Ground tissue#Sclerenchyma|Sclerenchyma]] is a tissue composed of two types of cells, [[sclereid]]s and [[fibres]] that have thickened, [[lignin|lignified]] secondary walls<ref name=Cutter>{{cite book|first=EG |last=Cutter |date=1977 |title=Plant Anatomy Part 1. Cells and Tissues |publisher=Edward Arnold |location=London |isbn=0713126388 }}</ref>{{rp|78}} laid down inside of the [[primary cell wall]]. The secondary walls harden the cells and make them impermeable to water. Consequently, sclereids and fibres are typically dead at functional maturity, and the cytoplasm is missing, leaving an empty central cavity. [[Sclereid]]s or stone cells, (from the Greek skleros, ''hard'') are hard, tough cells that give leaves or fruits a gritty texture. They may discourage herbivory by damaging digestive passages in small insect larval stages. Sclereids form the hard pit wall of peaches and many other fruits, providing physical protection to the developing kernel. [[Fibre]]s are elongated cells with lignified secondary walls that provide load-bearing support and tensile strength to the leaves and stems of herbaceous plants. Sclerenchyma fibres are not involved in conduction, either of water and nutrients (as in the [[xylem]]) or of carbon compounds (as in the [[phloem]]), but it is likely that they evolved as modifications of xylem and phloem initials in early land plants. [[Image:Arabidopsis-epiderm-conidiospore-hyaloperonospora-parasitica.jpg|thumb|right|cells of ''[[Arabidopsis thaliana]]'' [[Epidermis (botany)|epidermis]]]] ===Xylem=== [[Xylem]] is a complex vascular tissue composed of water-conducting [[tracheid]]s or [[vessel elements]], together with fibres and parenchyma cells. Tracheids<ref name=Tyree>MT Tyree; MH Zimmermann (2003) Xylem structure and the ascent of sap, 2nd edition, Springer-Verlag, New York USA</ref> are elongated cells with lignified secondary thickening of the cell walls, specialised for conduction of water, and first appeared in plants during their transition to land in the [[Silurian]] period more than 425 million years ago (see ''[[Cooksonia (plant)|Cooksonia]]''). The possession of xylem tracheids defines the [[vascular plants]] or Tracheophytes. Tracheids are pointed, elongated xylem cells, the simplest of which have continuous primary cell walls and lignified secondary wall thickenings in the form of rings, hoops, or reticulate networks. More complex tracheids with valve-like perforations called [[pit (botany)|bordered pits]] characterise the gymnosperms. The [[fern]]s and other [[pteridophyte]]s and the [[gymnosperm]]s have only xylem [[tracheid]]s, while the [[angiosperms|flowering plants]] also have [[vessel element|xylem vessel]]s. Vessel elements are hollow xylem cells without end walls that are aligned end-to-end so as to form long continuous tubes. The bryophytes lack true xylem tissue, but their [[sporophyte]]s have a water-conducting tissue known as the hydrome that is composed of elongated cells of simpler construction. ===Phloem=== [[Phloem]] is a specialised tissue for food transport in higher plants, mainly transporting [[sucrose]] along pressure gradients generated by osmosis, a process called [[Phloem#Function|translocation]]. Phloem is a complex tissue, consisting of two main cell types, the [[sieve tube element|sieve tubes]] and the intimately associated [[companion cell]]s, together with parenchyma cells, phloem fibres and sclereids.<ref name=Cutter/>{{rp|171}} Sieve tubes are joined end-to-end with perforated end-plates between known as ''[[sieve plate]]s'', which allow transport of photosynthate between the sieve elements. The sieve tube elements lack [[cell nucleus|nuclei]] and [[ribosome]]s, and their metabolism and functions are regulated by the adjacent nucleate companion cells. The companion cells, connected to the sieve tubes via [[plasmodesmata]], are responsible for loading the phloem with [[sugar]]s. The [[bryophyte]]s lack phloem, but [[moss]] [[sporophyte]]s have a simpler tissue with analogous function known as the leptome. [[File:Epidermal Cells of Plant Leaf..jpg|thumb|This is an electron micrograph of the epidermal cells of a Brassica chinensis leaf. The stomates are also visible.]] ===Epidermis=== The [[Epidermis (botany)|plant epidermis]] is specialised tissue, composed of parenchyma cells, that covers the external surfaces of leaves, stems and roots. Several cell types may be present in the epidermis. Notable among these are the stomatal guard cells that control the rate of [[Gas exchange#Plants|gas exchange]] between the plant and the atmosphere, glandular and clothing hairs or [[trichome]]s, and the [[root hair]]s of primary roots. In the shoot epidermis of most plants, only the [[stomata|guard cells]] have chloroplasts. Chloroplasts contain the green pigment chlorophyll which is needed for photosynthesis. The epidermal cells of aerial organs arise from the superficial layer of cells known as the ''tunica'' (L1 and L2 layers) that covers the plant [[meristem|shoot apex]],<ref name="Cutter"/> whereas the cortex and vascular tissues arise from innermost layer of the shoot apex known as the ''corpus'' (L3 layer). The epidermis of roots originates from the layer of cells immediately beneath the root cap. The epidermis of all aerial organs, but not roots, is covered with a [[plant cuticle|cuticle]] made of [[polyester]] [[cutin]] or polymer [[Cutan (polymer)|cutan]] (or both), with a superficial layer of [[epicuticular wax]]es. The epidermal cells of the primary shoot are thought to be the only plant cells with the biochemical capacity to synthesize cutin.<ref name="Kolattukudy 1996">Kolattukudy, PE (1996) Biosynthetic pathways of cutin and waxes, and their sensitivity to [[environmental stresses]]. In: Plant Cuticles. Ed. by G. Kerstiens, BIOS Scientific publishers Ltd., Oxford, pp 83β108</ref> == See also == {{div col}} *[[Animal cell]] *[[Cell nucleus]] *[[Chloroplast]] *[[Chromatin]] *[[Cytoplasm]] *[[Cytoskeleton]] *[[Golgi apparatus]] *[[Leucoplast]] *[[Mitochondrion]] *[[Nuclear envelope]] *[[Nucleolus]] *[[Paul Nurse]] *[[Wall-associated kinase]] {{div col end}} ==References== {{Reflist}} {{Botany}} {{Authority control}} {{DEFAULTSORT:Plant Cell}} [[Category:Plant cells| ]] [[Category:Plant anatomy]] [[Category:Eukaryotic cells]]
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