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An intracellular compartment, bounded by a single membrane bilayer, which functions as a primary site of protein and metabolite degradation and recycling in animals, but serves additional complex functions in fungi and plants (see illustration). Scientists who study vacuoles also define them as the terminal product of the secretory pathway. The secretory pathway functions to transport protein and metabolite-containing membrane vesicles from sites of synthesis or uptake to the vacuole. See Cell membranes, Cell metabolism, Golgi apparatus, Secretion

Electron micrograph of a barley root tip cell, showing multiple vacuoles within the cytoplasmenlarge picture
Electron micrograph of a barley root tip cell, showing multiple vacuoles within the cytoplasm

In animals, a lytic vacuole known as the lysosome typically functions to process macromolecules. Such macromolecules can be targeted to the lysosome from sites of synthesis. For example, proteins that assemble incorrectly in the endoplasmic reticulum (ER) can be degraded in the lysosome and their constituent amino acids recycled. Proteins that can serve as nutrients are also targeted to the lysosome from the cell surface. An important process for the recycling of cytoplasm in eukaryotic cells is autophagy, in which molecules or organelles are encapsulated in membrane vesicles that fuse with the lysosome. See Endocytosis, Endoplasmic reticulum, Lysosome

In the mammalian immune system, macrophages and neutrophils take up particles and pathogens in the process of phagocytosis, during which the pathogen is eventually digested in the lysosome. A number of diseases in humans can be caused when intracellular pathogens evade destruction in the lysosome. See Phagocytosis

In fungi, vacuoles can serve functions not found in animals. Besides a lytic function, they serve in the storage of ions as well as amino acids for protein synthesis. In yeast, vacuoles can also function in the destruction and recycling of cellular organelles, such as peroxisomes, which help protect the cell from toxic oxygen-containing molecules. The process of peroxisome digestion by vacuoles is known as pexophagy.

The most complex vacuoles are found in plants. Some contain hydrolytic enzymes and store ions similar to those found in lysosomes, whereas others serve a role in storing pigments which impart color to flowers to attract pollinators. Specialized ER-derived vacuoles in plant seeds, known as protein bodies, function in the storage of proteins called prolamines that are common in the endosperm of cereals. Upon germination, the proteins are degraded and used as a source of amino acids and nitrogen for the growing plant. Toxins, such as alkaloids, are stored in vacuoles in parts of the plant, such as the leaves, which are subject to frequent herbivory. Scientists have learned that plants produce and store in their vacuoles a vast array of unique chemicals which may, in addition to their natural functions, have medicinal value. See Plant cell

Another unique function that vacuoles serve in plants is in cell growth. As a consequence of the accumulation of ions, metabolites, and water, plant vacuoles are under considerable internal osmotic pressure. The vacuolar membrane in plants, known as the tonoplast, as well as the cell itself would burst under this pressure if not for the rigid wall that surrounds the cells. The resulting turgor pressure provides mechanical stability to plant stems. Loss of osmotic pressure in the vacuole due to a lack of water results in plant wilting. The osmotic pressure of the vacuoles also provides the driving force that allows plants to grow by enlarging their cell volume. Enzymes reduce the rigidity of the cell wall, which permits cell expansion under the force of turgor. This is a fundamental process in plants and explains why vacuoles can occupy as much as 95% of the volume of some cells. See Cell walls (plant)

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.


(cell and molecular biology)
A membrane-bound cavity within a cell; may function in digestion, storage, secretion, or excretion.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
In our study, the commonest histopathological features recognized were saw-toothed rete ridges/ irregular acanthosis seen in 85%, vacuolar degeneration of basal layer in 81.7%, band-like infiltrate in 71.7%, hyperkeratosis/ orthokeratosis in 63.3% and wedge-shaped hypergranulosis in 61.7% of cases followed by Civatte bodies in 45%, melanophages in upper dermis in 43.3%, pigment incontinence in 41.7%, perivascular infiltrate in 28.3% and Max-Joseph spaces in 16.7% of cases.
Yoshida, "Vacuolar membrane lesions induced by a freeze-thaw cycle in protoplasts isolated from deacclimated tubers of Jerusalem artichoke (Helianthus tuberosus L.)," Plant and Cell Physiology, vol.
In patients with DI-SCLE, the histological examination of a skin biopsy often indicates vacuolar degeneration of the epidermal basal layer, necrotic keratinocytes, and lymphocytic interface dermatitis.
Photomicrograph of kidney of (a) control mouse showing normal structure, (b) C[Cl.sub.4]-treated mouse had vacuolar degenerative changes in the renal epithelium, (c) C[Cl.sub.4]-treated mouse had early necrotic changes, (d) C[Cl.sub.4] treated mouse had congestion of renal blood vessels, (e) C[Cl.sub.4]-treated mouse had focal leucocytic infiltrations, (f) C[Cl.sub.4]-kefir treated mouse had moderate improvement of renal lesions and mild vacuolar degenerative changes in the renal epithelium with absence of necrotic changes, and (g) C[Cl.sub.4]-kefir treated mouse had mild congestion of renal blood vessels with no focal inflammatory reaction
Morphologic changes of the heart (200x magnification (d, e, f)) and liver (400x magnification (g, h, i)) were processed for HE staining at 30 days (short arrows for infiltrated inflammatory cells and long arrows for focal myolysis; yellow arrowheads for karyopyknosis and black arrowheads for vacuolar degeneration).
Endomyocardial biopsy revealed vacuolar changes in the myocardial cells (especially around nucleus) and perimysial fibrosis without inflammatory cells (Figure 2(a)).
The nuclei and the surrounding boundary were not clearly demarcated, and the presence of nuclear enrichment, fusion, membrane disappearance, and granular denaturation, as well as vacuolar degeneration, were also observed in the 1/3 [LD.sub.50] treatment group (Figure 4(M-5)).
Skin biopsies were obtained from his right extensor arm and anterior chest which revealed a vacuolar interface dermatitis with dermal mucin deposition.
However, liver tissue samples from the MTX group showed focal areas of necrosis around the central vein, sinusoidal dilatation, vacuolar degeneration, and focal infiltration with leukocytes, mainly lymphocytes.
Carrasco, "Requirement for vacuolar proton-ATPase activity during entry of influenza virus into cells," The Journal of Virology, vol.
In transgenic cotton, overexpression of the Arabidopsis gene AtNHX1 that encodes a vacuolar [Na.sup.+]/[H.sup.+] antiporter resulted in higher photosynthetic performance and higher nitrogen assimilation rates as compared with wild-type cotton plants.