Vacuole

Antonie van Leeuwenhoek described the plant vacuole in 1676.van Leeuwenhoek, A. and Hoole, S. (1800) The Select Works of Antony Van Leeuwenhoek, Containing His Microscopical Discoveries in Many of the Works of Nature. Translator; 1800 Contractile vacuoles ("stars") were first observed by Spallanzani (1776) in protozoa, although mistaken for respiratory organs.{{cite journal|vauthors=Spallanzani L|date=1776|title=Observations et expériences faites sur les Animalicules des Infusions|journal=L'École Polytechnique|location=Paris|pages=1920}} Dujardin (1841) named these "stars" as vacuoles.{{cite journal|vauthors=Dujardin F|date=1841|title=Histoire naturelle des zoophytes: Infusoires|journal=Librairie Encyclopédique de Roret|location=Paris}} In 1842, Schleiden applied the term for plant cells, to distinguish the structure with cell sap from the rest of the protoplasm.{{cite book|vauthors=Schleiden MJ|date=1842|title=Grundzüge der wissenschaftlichen Botanik|location=Leipzig|publisher=W. Engelmann}}{{cite book|url=https://books.google.com/books?id=t_biw80LgjwC|title=Plant Cell Biology: From Astronomy to Zoology|vauthors=Wayne R|date=2009|publisher=Elsevier/Academic Press|isbn=9780080921273|location=Amsterdam|page=101}} In 1885, de Vries named the vacuole membrane as tonoplast.{{cite journal|vauthors=de Vries H|date=1885|title=Plasmolytische Studien über die Wand der Vakuolen|journal=Jahrb. Wiss. Bot.|volume=16|pages=465–598}}

Christian de Duve, discovered mammalian lysosomes using biochemical methods in the mid 1970’s. de Duve named lysosomes based on their biochemical properties (from the Greek lysis – digestive and soma – body). Their physical form was confirmed shortly later by electron microscopy. Because the lysosome shares many properties with vacuoles across taxonomical kingdoms, the notion that vacuoles and lysosomes are distinctly different organelles is more historical than functional.de Duve, C. (2005) The lysosome turns fifty. Nat. Cell Biol. 7, 847–849 CrossRef PubMed

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 internal hydrostatic pressure or turgor within the cell
• Maintaining an acidic internal pH
• 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.{{cite journal|vauthors=Okubo-Kurihara E, Sano T, Higaki T, Kutsuna N, Hasezawa S|date=January 2009|title=Acceleration of vacuolar regeneration and cell growth by overexpression of an aquaporin NtTIP1;1 in tobacco BY-2 cells|journal=Plant & Cell Physiology|volume=50|issue=1|pages=151–60|doi=10.1093/pcp/pcn181|pmid=19042915|doi-access=free}}
• In seeds, storing proteins needed for germination (these are kept in 'protein bodies', which are modified vacuoles).{{cite book|last=Matile|first=Phillipe|title=Discoveries in Plant Biology|date=1993|publisher=World Scientific Publishing Co Pte Ltd|volume=1|chapter=Chapter 18: Vacuoles, discovery of lysosomal origin|name-list-style=vanc}}

Vacuoles also play a major role in autophagy, maintaining a balance between biogenesis (production) and degradation (or turnover), of many substances and cell structures in certain organisms. They also aid in the lysis and recycling of misfolded proteins that have begun to build up within the cell. Thomas Boller[http://plantbiology.unibas.ch/people/boller/boller.htm Thomas Boller] {{Webarchive|url=https://web.archive.org/web/20131206010355/http://plantbiology.unibas.ch/people/boller/boller.htm|date=2013-12-06}}. Plantbiology.unibas.ch. Retrieved on 2011-09-02. and others proposed that the vacuole participates in the destruction of invading bacteria and Robert B. Mellor proposed organ-specific forms have a role in 'housing' symbiotic bacteria. In protists,{{efn|For example the food vacuole in Plasmodium.}} 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.{{cite journal|vauthors=Jezbera J, Hornák K, Simek K|date=May 2005|title=Food selection by bacterivorous protists: insight from the analysis of the food vacuole content by means of fluorescence in situ hybridization|journal=FEMS Microbiology Ecology|volume=52|issue=3|pages=351–63|doi=10.1016/j.femsec.2004.12.001|pmid=16329920|doi-access=free}}

In animal cells, vacuoles perform mostly subordinate roles, assisting in larger processes of exocytosis and endocytosis.

Animal vacuoles are smaller than their plant counterparts but also usually greater in number.{{cite book|author=Becker B|url=https://archive.org/details/internationalrev0000unse_w6f2/page/1|title=Function and evolution of the vacuolar compartment in green algae and land plants (Viridiplantae)|year=2007|isbn=9780123742636|series=International Review of Cytology|volume=264|pages=[https://archive.org/details/internationalrev0000unse_w6f2/page/1 1–24]|doi=10.1016/S0074-7696(07)64001-7|pmid=17964920}} There are also animal cells that do not have any vacuoles.[http://www.biology-online.org/11/1_plant_cells_vs_animal_cells.htm Plant cells vs. Animal cells] {{Webarchive|url=https://web.archive.org/web/20190201065519/https://www.biology-online.org/11/1_plant_cells_vs_animal_cells.htm|date=2019-02-01}}. Biology-Online.org

Exocytosis is the extrusion process of proteins and lipids from the cell. These materials are absorbed into secretory granules within the Golgi apparatus before 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. The invagination is 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.{{cite book|author=William F. Ganong, MD|title=Review of medical physiology|year=2003|edition=21st}} Phagocytosis and pinocytosis are both undertaken in association with lysosomes which complete the breakdown of the material which has been engulfed.{{cite book|author=Reggiori F|title=Current Topics in Developmental Biology Volume 74|year=2006|isbn=9780121531744|volume=74|pages=1–30|chapter=Membrane Origin for Autophagy|doi=10.1016/S0070-2153(06)74001-7|pmc=7112310|pmid=16860663}}

Salmonella is able to survive and reproduce in the vacuoles of several mammal species after being engulfed.{{cite journal|vauthors=Knodler LA, Steele-Mortimer O|date=September 2003|title=Taking possession: biogenesis of the Salmonella-containing vacuole|journal=Traffic|volume=4|issue=9|pages=587–99|doi=10.1034/j.1600-0854.2003.00118.x|pmid=12911813|s2cid=25646573|doi-access=free}}

The vacuole probably evolved several times independently, even within the Viridiplantae.

File:Rhoeo_Discolor_-_Plasmolysis.jpg-storing vacuoles of Rhoeo spathacea, a spiderwort, in cells that have plasmolyzed]]

Most mature plant cells have 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.{{cite book|url=https://archive.org/details/molecularbiology00albe_292|title=Molecular Biology of the Cell|vauthors=Alberts B, Johnson B, Lewis A, Raff J, Roberts K, Walter P|date=2008|publisher=Garland Science|isbn=978-0-8153-4111-6|edition=Fifth|location=New York|page=[https://archive.org/details/molecularbiology00albe_292/page/n814 781]|url-access=limited}} Strands of cytoplasm often run through the vacuole.

A vacuole is surrounded by a membrane called the tonoplast (word origin: Gk tón(os) + -o-, meaning “stretching”, “tension”, “tone” + comb. form repr. Gk plastós formed, molded) and filled with cell sap. Also called the vacuolar 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.{{cite journal|vauthors=Li WY, Wong FL, Tsai SN, Phang TH, Shao G, Lam HM|date=June 2006|title=Tonoplast-located GmCLC1 and GmNHX1 from soybean enhance NaCl tolerance in transgenic bright yellow (BY)-2 cells|journal=Plant, Cell & Environment|volume=29|issue=6|pages=1122–37|doi=10.1111/j.1365-3040.2005.01487.x|pmid=17080938|doi-access=free}}

Transport of protons from the cytosol to the vacuole stabilizes cytoplasmic pH, while making the vacuolar interior more acidic creating a proton motive force which the cell can use to transport nutrients into or out of the vacuole. The low pH of the vacuole also allows degradative enzymes to 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 the meristems contain small provacuoles and cells of the vascular cambium have 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 maintain turgor pressure against the cell wall. Proteins found in the tonoplast (aquaporins) control the flow of water into and out of the vacuole through active transport, pumping potassium (K⁺) ions into and out of the vacuolar interior. Due to osmosis, water will diffuse into the vacuole, placing pressure on the cell wall. If water loss leads to a significant decline in turgor pressure, the cell will plasmolyze. Turgor pressure exerted by vacuoles is also required for cellular elongation: as the cell wall is partially degraded by the action of expansins, 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 the chloroplasts closer to light.{{cite book|last1=Taiz|first1=Lincoln|title=Plant Physiology|last2=Zeiger|first2=Eduardo|date=2002|publisher=Sinauer|isbn=0-87893-856-7|edition=3rd|pages=13–14|name-list-style=vanc}} Most plants store chemicals in the vacuole that react with chemicals in the cytosol. If the cell is broken, for example by a herbivore, then the two chemicals can react forming toxic chemicals. In garlic, alliin and the enzyme alliinase are normally separated but form allicin if the vacuole is broken. A similar reaction is responsible for the production of syn-propanethial-S-oxide when onions are cut.{{Citation needed|date=August 2010}}

Vacuoles in fungal cells perform similar functions to those in plants and there can be more than one vacuole per cell. In yeast cells the vacuole (Vac7) is a dynamic structure that can rapidly modify its morphology. They are involved in many processes including the homeostasis of cell pH and the concentration of ions, osmoregulation, storing amino acids and polyphosphate and degradative processes. Toxic ions, such as strontium ({{chem|Sr|2+}}), cobalt(II) ({{chem|Co|2+}}), and lead(II) ({{chem|Pb|2+}}) are transported into the vacuole to isolate them from the rest of the cell.{{cite journal|vauthors=Klionsky DJ, Herman PK, Emr SD|date=September 1990|title=The fungal vacuole: composition, function, and biogenesis|journal=Microbiological Reviews|volume=54|issue=3|pages=266–92|doi=10.1128/MMBR.54.3.266-292.1990|pmc=372777|pmid=2215422}}

A contractile vacuole is a specialized osmoregulatory organelle that is present in many free-living protists.{{Cite journal|last1=Essid|first1=Miriam|last2=Gopaldass|first2=Navin|last3=Yoshida|first3=Kunito|last4=Merrifield|first4=Christien|last5=Soldati|first5=Thierry|date=April 2012|editor-last=Brennwald|editor-first=Patrick|title=Rab8a regulates the exocyst-mediated kiss-and-run discharge of the Dictyostelium contractile vacuole|journal=Molecular Biology of the Cell|language=en|volume=23|issue=7|pages=1267–1282|doi=10.1091/mbc.e11-06-0576|issn=1059-1524|pmc=3315810|pmid=22323285}} 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.{{Cite journal|last=Plattner|first=Helmut|date=2015-04-03|title=The contractile vacuole complex of protists – New cues to function and biogenesis|url=http://www.tandfonline.com/doi/full/10.3109/1040841X.2013.821650|journal=Critical Reviews in Microbiology|language=en|volume=41|issue=2|pages=218–227|doi=10.3109/1040841X.2013.821650|pmid=23919298|s2cid=11384111|issn=1040-841X}} 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.{{Cite journal|last1=Pappas|first1=George D.|last2=Brandt|first2=Philip W.|date=1958|title=The Fine Structure of the Contractile Vacuole in Ameba|url= |journal=The Journal of Biophysical and Biochemical Cytology|volume=4|issue=4|pages=485–488|doi=10.1083/jcb.4.4.485|jstor=1603216|pmid=13563556|pmc=2224495|issn=0095-9901}}

Food vacuoles (also called digestive vacuole{{Cite web|title=Food vacuole {{!}} biology|url=https://www.britannica.com/science/food-vacuole|access-date=2021-02-21|website=Encyclopedia Britannica|language=en}}) are organelles found in certain protists, such as ciliates,{{cite journal|vauthors=Mast SO|title=The Food-Vacuole in Paramecium|journal=The Biological Bulletin|volume=92|issue=1|year=1947|doi=10.2307/1537967|pmid=20284992|pages=31-72|jstor=1537967}}{{cite journal|vauthors=Goff LJ, Stein JR|journal=Protoplasma|volume=107|pages=235-254|year=1981|doi=10.1007/BF01276828|title=Digestion in the Peritrich Ciliate Ophrydium versatile}} amoeboids{{cite journal|vauthors=Mast SO|title=The Hydrogen Ion Concentration of the Content of the Food Vacuoles and the Cytoplasm in Amoeba and Other Phenomena Concerning the Food Vacuoles|journal=The Biological Bulletin|volume=83|issue=2|year=1942|doi=10.2307/1538142|pages=173-204|jstor=1538142}} and Plasmodium falciparum,{{cite journal|vauthors=Jackson KE, Klonis N, Ferguson DJ, Adisa A, Dogovski C, Tilley L|year=2004|title=Food vacuole-associated lipid bodies and heterogeneous lipid environments in the malaria parasite, Plasmodium falciparum|journal=Molecular Microbiology|volume=54|issue=1|pages=109-122|doi=10.1111/j.1365-2958.2004.04284.x|doi-access=free}}{{cite journal|vauthors=Biagini GA, Bray PG, Spiller DG, White MR, Ward SA|title=The digestive food vacuole of the malaria parasite is a dynamic intracellular Ca2+ store|year=2003|volume=278|issue=30|pages=27910-27915|doi=10.1074/jbc.M304193200|doi-access=free|pmid=12740366|journal=Journal of Biological Chemistry}} a protozoan parasite that causes malaria.

In Paramecium, the food vacuoles can show variation in size and shape based on their contents, solute balance and timing of ingestion in the cellular pharynx. The vacuoles of Ophrydium versatile undergo discoidal vesicle membrane recycling to the cytostome, condensing in the process, then associate with rough endoplasmic reticulum, receive protein coating on their cytosolic or exterior face from fusion with cup-shaped coated vesicles and condense again while producing cup-shaped coated vesicles, possibly for the purpose of enzyme recycling, prior to cytoproct egestion of residues mediated by vacuole fusion.

The food vacuoles of Plasmodium falciparum have been found to have calcium storage properties mediated by active transport and associated with vacuole acidification that are important for P. falciparum asexual reproduction.

In histopathology, vacuolization is the formation of vacuoles or vacuole-like structures, within or adjacent to cells. It is an unspecific sign of disease.{{Citation needed|date=February 2021}}

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