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Vacuole

From Wikipedia, the free encyclopedia
Not to be confused withvesicle (biology and chemistry).
Cell biology
Animal cell diagram
Components of a typical animal cell:
  1. Nucleolus
  2. Nucleus
  3. Ribosome(dots as part of 5)
  4. Vesicle
  5. Rough endoplasmic reticulum
  6. Golgi apparatus(or, Golgi body)
  7. Cytoskeleton
  8. Smooth endoplasmic reticulum
  9. Mitochondrion
  10. Vacuole
  11. Cytosol(fluid that containsorganelles;with which, comprisescytoplasm)
  12. Lysosome
  13. Centrosome
  14. Cell membrane
Plant cell structure
Animal cell structure

Avacuole(/ˈvækjuːoʊl/) is amembrane-bound organellewhich is present inplantandfungalcellsand someprotist,animal,andbacterialcells.[1][2]Vacuoles are essentially enclosed compartments which are filled with water containing inorganic and organic molecules includingenzymesinsolution,though in certain cases they may contain solids which have been engulfed. Vacuoles are formed by the fusion of multiple membranevesiclesand are effectively just larger forms of these.[3]The organelle has no basic shape or size; its structure varies according to the requirements of the cell.

Discovery

Contractile vacuoles( "stars" ) were first observed bySpallanzani(1776) inprotozoa,although mistaken for respiratory organs.Dujardin(1841) named these "stars" asvacuoles.In 1842,Schleidenapplied the term for plant cells, to distinguish the structure with cell sap from the rest of theprotoplasm.[4][5][6][7]

In 1885,de Vriesnamed the vacuole membrane as tonoplast.[8]

Function

The function and significance of vacuoles varies greatly according to the type of cell in which they are present, having much greater prominence in the cells of plants, fungi and certain protists than those of animals and bacteria. In general, the functions of the vacuole include:

  • Isolating materials that might be harmful or a threat to the cell
  • Containing waste products
  • Containing water in plant cells
  • Maintaining internalhydrostatic pressureorturgorwithin the cell
  • Maintaining anacidicinternalpH
  • Containing small molecules
  • Exporting unwanted substances from the cell
  • Allowing plants to support structures such as leaves and flowers due to the pressure of the central vacuole
  • By increasing in size, allowing the germinating plant or its organs (such as leaves) to grow very quickly and through using up mostly just water.[9]
  • In seeds, storing proteins needed for germination (these are kept in 'protein bodies', which are modified vacuoles).[10]

Vacuoles also play a major role inautophagy,maintaining a balance betweenbiogenesis(production) and degradation (or turnover), of many substances and cell structures in certain organisms. They also aid in thelysisand recycling of misfolded proteins that have begun to build up within the cell. Thomas Boller[11]and others proposed that the vacuole participates in the destruction of invadingbacteriaandRobert B. Mellorproposed organ-specific forms have a role in 'housing' symbiotic bacteria. In protists,[12]vacuoles have the additional function of storing food which has been absorbed by the organism and assisting in the digestive and waste management process for the cell.[13]

In animal cells, vacuoles perform mostly subordinate roles, assisting in larger processes ofexocytosisandendocytosis.

Animal vacuoles are smaller than their plant counterparts but also usually greater in number.[14]There are also animal cells that do not have any vacuoles.[15]

Exocytosis is the extrusion process of proteins and lipids from the cell. These materials are absorbed into secretory granules within theGolgi apparatusbefore being transported to the cell membrane and secreted into the extracellular environment. In this capacity, vacuoles are simply storage vesicles which allow for the containment, transport and disposal of selected proteins and lipids to the extracellular environment of the cell.

Endocytosis is the reverse of exocytosis and can occur in a variety of forms.Phagocytosis( "cell eating" ) is the process by which bacteria, dead tissue, or other bits of material visible under the microscope are engulfed by cells. The material makes contact with the cell membrane, which then invaginates. Theinvaginationis pinched off, leaving the engulfed material in the membrane-enclosed vacuole and the cell membrane intact.Pinocytosis( "cell drinking" ) is essentially the same process, the difference being that the substances ingested are in solution and not visible under the microscope.[16]Phagocytosis and pinocytosis are both undertaken in association withlysosomeswhich complete the breakdown of the material which has been engulfed.[17]

Salmonellais able to survive and reproduce in the vacuoles of severalmammalspecies after being engulfed.[18]

The vacuole probably evolved several times independently, even within theViridiplantae.[14]

Types

Central

Theanthocyanin-storing vacuoles ofRhoeo spathacea,aspiderwort,in cells that have plasmolyzed

Most matureplant cellshave one large vacuole that typically occupies more than 30% of the cell's volume, and that can occupy as much as 80% of the volume for certain cell types and conditions.[19]Strands ofcytoplasmoften run through the vacuole.

A vacuole is surrounded by a membrane called thetonoplast(word origin: Gk tón(os) + -o-, meaning “stretching”, “tension”, “tone” + comb. form repr. Gk plastós formed, molded) and filled withcell sap.Also called thevacuolar membrane,the tonoplast is the cytoplasmic membrane surrounding a vacuole, separating the vacuolar contents from the cell's cytoplasm. As a membrane, it is mainly involved in regulating the movements of ions around the cell, and isolating materials that might be harmful or a threat to the cell.[20]

Transport ofprotonsfrom the cytosol to the vacuole stabilizes cytoplasmicpH,while making the vacuolar interior more acidic creating aproton motive forcewhich the cell can use to transport nutrients into or out of the vacuole. The low pH of the vacuole also allowsdegradative enzymesto act. Although single large vacuoles are most common, the size and number of vacuoles may vary in different tissues and stages of development. For example, developing cells in themeristemscontain small provacuoles and cells of thevascular cambiumhave many small vacuoles in the winter and one large one in the summer.

Aside from storage, the main role of the central vacuole is to maintainturgorpressure against thecell wall.Proteins found in the tonoplast (aquaporins) control the flow of water into and out of the vacuole throughactive transport,pumpingpotassium(K+)ionsinto and out of the vacuolar interior. Due toosmosis,water will diffuse into the vacuole, placing pressure on the cell wall. If water loss leads to a significant decline in turgor pressure, thecellwillplasmolyze.Turgor pressure exerted by vacuoles is also required for cellular elongation: as the cell wall is partially degraded by the action ofexpansins,the less rigid wall is expanded by the pressure coming from within the vacuole. Turgor pressure exerted by the vacuole is also essential in supporting plants in an upright position. Another function of a central vacuole is that it pushes all contents of the cell's cytoplasm against the cellular membrane, and thus keeps thechloroplastscloser to light.[21]Most plants store chemicals in the vacuole that react with chemicals in the cytosol. If the cell is broken, for example by aherbivore,then the two chemicals can react forming toxic chemicals. In garlic,alliinand the enzymealliinaseare normally separated but formallicinif the vacuole is broken. A similar reaction is responsible for the production ofsyn-propanethial-S-oxidewhenonionsare cut.[citation needed]

Vacuoles in fungal cells perform similar functions to those in plants and there can be more than one vacuole per cell. Inyeastcells the vacuole (Vac7) is adynamicstructure that can rapidly modify itsmorphology.They are involved in many processes including thehomeostasisof cell pH and the concentration of ions,osmoregulation,storingamino acidsandpolyphosphateand degradative processes. Toxic ions, such asstrontium(Sr2+
),cobalt(II) (Co2+
), andlead(II) (Pb2+
) are transported into the vacuole to isolate them from the rest of the cell.[22]

Contractile

Acontractile vacuoleis a specialized osmoregulatory organelle that is present in many free-living protists.[23]The contractile vacuole is part of the contractile vacuole complex which includes radial arms and a spongiome. The contractile vacuole complex works periodically contracts to remove excess water and ions from the cell to balance water flow into the cell.[24]When the contractile vacuole is slowly taking water in, the contractile vacuole enlarges, this is called diastole and when it reaches its threshold, the central vacuole contracts then contracts (systole) periodically to release water.[25]

Digestive

Food vacuoles(also calleddigestive vacuole[26]) are organelles found inCiliates,andPlasmodium falciparum,a protozoan parasite that causesMalaria.

Histopathology

Inhistopathology,vacuolizationis the formation of vacuoles or vacuole-like structures, within or adjacent to cells. It is an unspecific sign of disease.[citation needed]

References

  1. ^Venes D (2001).Taber's Cyclopedic Medical Dictionary(Twentieth ed.). Philadelphia: F.A. Davis Company. p. 2287.ISBN0-9762548-3-2.
  2. ^Schulz-Vogt HN (2006). "Vacuoles".Inclusions in Prokaryotes.Microbiology Monographs. Vol. 1. pp. 295–298.doi:10.1007/3-540-33774-1_10.ISBN978-3-540-26205-3.
  3. ^Brooker RJ, Widmaier EP, Graham LE, Stiling PD (2007).Biology(First ed.). New York: McGraw-Hill. pp.79.ISBN978-0-07-326807-1.
  4. ^Spallanzani L (1776). "Observations et expériences faites sur les Animalicules des Infusions".L'École Polytechnique.Paris: 1920.
  5. ^Dujardin F (1841). "Histoire naturelle des zoophytes: Infusoires".Librairie Encyclopédique de Roret.Paris.
  6. ^Schleiden MJ (1842).Grundzüge der wissenschaftlichen Botanik.Leipzig: W. Engelmann.
  7. ^Wayne R (2009).Plant Cell Biology: From Astronomy to Zoology.Amsterdam: Elsevier/Academic Press. p. 101.ISBN9780080921273.
  8. ^de Vries H (1885). "Plasmolytische Studien über die Wand der Vakuolen".Jahrb. Wiss. Bot.16:465–598.
  9. ^Okubo-Kurihara E, Sano T, Higaki T, Kutsuna N, Hasezawa S (January 2009)."Acceleration of vacuolar regeneration and cell growth by overexpression of an aquaporin NtTIP1;1 in tobacco BY-2 cells".Plant & Cell Physiology.50(1): 151–60.doi:10.1093/pcp/pcn181.PMID19042915.
  10. ^Matile P (1993). "Chapter 18: Vacuoles, discovery of lysosomal origin".Discoveries in Plant Biology.Vol. 1. World Scientific Publishing Co Pte Ltd.
  11. ^Thomas BollerArchived2013-12-06 at theWayback Machine.Plantbiology.unibas.ch. Retrieved on 2011-09-02.
  12. ^For example thefood vacuole inPlasmodium.
  13. ^Jezbera J, Hornák K, Simek K (May 2005)."Food selection by bacterivorous protists: insight from the analysis of the food vacuole content by means of fluorescence in situ hybridization".FEMS Microbiology Ecology.52(3): 351–63.doi:10.1016/j.femsec.2004.12.001.PMID16329920.
  14. ^abBecker B (2007).Function and evolution of the vacuolar compartment in green algae and land plants (Viridiplantae).International Review of Cytology. Vol. 264. pp.1–24.doi:10.1016/S0074-7696(07)64001-7.ISBN9780123742636.PMID17964920.
  15. ^Plant cells vs. Animal cellsArchived2019-02-01 at theWayback Machine.Biology-Online.org
  16. ^William F. Ganong, MD (2003).Review of medical physiology(21st ed.).
  17. ^Reggiori F (2006). "Membrane Origin for Autophagy".Current Topics in Developmental Biology Volume 74.Vol. 74. pp. 1–30.doi:10.1016/S0070-2153(06)74001-7.ISBN9780121531744.PMC7112310.PMID16860663.
  18. ^Knodler LA, Steele-Mortimer O (September 2003)."Taking possession: biogenesis of the Salmonella-containing vacuole".Traffic.4(9): 587–99.doi:10.1034/j.1600-0854.2003.00118.x.PMID12911813.S2CID25646573.
  19. ^Alberts B, Johnson B, Lewis A, Raff J, Roberts K, Walter P (2008).Molecular Biology of the Cell(Fifth ed.). New York: Garland Science. p.781.ISBN978-0-8153-4111-6.
  20. ^Li WY, Wong FL, Tsai SN, Phang TH, Shao G, Lam HM (June 2006)."Tonoplast-located GmCLC1 and GmNHX1 from soybean enhance NaCl tolerance in transgenic bright yellow (BY)-2 cells".Plant, Cell & Environment.29(6): 1122–37.doi:10.1111/j.1365-3040.2005.01487.x.PMID17080938.
  21. ^Taiz L, Zeiger E (2002).Plant Physiology(3rd ed.). Sinauer. pp. 13–14.ISBN0-87893-856-7.
  22. ^Klionsky DJ, Herman PK, Emr SD (September 1990)."The fungal vacuole: composition, function, and biogenesis".Microbiological Reviews.54(3): 266–92.doi:10.1128/MMBR.54.3.266-292.1990.PMC372777.PMID2215422.
  23. ^Essid, Miriam; Gopaldass, Navin; Yoshida, Kunito; Merrifield, Christien; Soldati, Thierry (April 2012). Brennwald, Patrick (ed.)."Rab8a regulates the exocyst-mediated kiss-and-run discharge of the Dictyostelium contractile vacuole".Molecular Biology of the Cell.23(7): 1267–1282.doi:10.1091/mbc.e11-06-0576.ISSN1059-1524.PMC3315810.PMID22323285.
  24. ^Plattner, Helmut (2015-04-03)."The contractile vacuole complex of protists – New cues to function and biogenesis".Critical Reviews in Microbiology.41(2): 218–227.doi:10.3109/1040841X.2013.821650.ISSN1040-841X.PMID23919298.S2CID11384111.
  25. ^Pappas, George D.; Brandt, Philip W. (1958)."The Fine Structure of the Contractile Vacuole in Ameba".The Journal of Biophysical and Biochemical Cytology.4(4): 485–488.doi:10.1083/jcb.4.4.485.ISSN0095-9901.JSTOR1603216.PMC2224495.PMID13563556.
  26. ^"Food vacuole | biology".Encyclopedia Britannica.Retrieved2021-02-21.
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