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Related to vacuole: contractile vacuole


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 ?
Signet ring cells contain an eccentric nucleus displaced by a single clear to lightly eosinophilic vacuole. Nuclei are bland with smooth contours and uniform chromatin, and mitoses are rare.
Intracellular inclusions (parasitophorous vacuoles) in the epithelia of the mantle, gills, labial palps, and digestive tract were observed; these tissues were different in respect of uninfected tissues (negative control) on cellular appearance (Fig.
Mitochondria and smooth endoplasmic reticulum aggregates of control oocyte (a), GV oocyte after IVM(b), vitrified--thawed GV oocyte after IVM (c), vitrified-thawed GV oocyte before IVM (d), M = mitochondria, SER = smooth endoplasmic reticulum, V = vacuole.
Also, myelinlike cytoplasmic inclusions, figures similar to mitophagy, and large vacuoles similar to autophagic vacuoles, indicating intense autophagy, were observed.
(a) Adipogenic differentiation was examined by lipid vacuole formation and Oil red O staining (red), as indicated, suggesting no adipogenesis in MSCs-L.
While the culture revealed no growth, cytologic examination identified mononuclear phagocytes with cytoplasmic vacuoles containing structures consistent with bacteria.
The score of each spermatozoon was determined as: (2xHead)+(3xVacuole)+ (Base); (Normal head score=2), (Lack of vacuole score=3), (Normal base score=1) and (Total score =6) for a morphologic "normal top" spermatozoon.
Accumulation of MDC in autophagy vacuoles was measured using a Fluostar Omega plate reader (BMG LABTECH Inc., NC, USA) with excitation and emission wavelength set at 355 nm and 540 nm.
No apical canalicular system (ACS) structure as well as no single large-size vacuole was observed (Figure 2).
[5] wrote about two brain tumour cases bearing obvious ependymal traits but also displaying the unusual presence of scattered cells with a single large vacuole compressing the nucleus into a crescent at one edge of the cytoplasm, shaped, thus, in the classical morphology of signet-ring cells.
A quadriceps muscle biopsy was performed and histopathology showed basophilic atrophic nonnecrotic myofibers in clusters with rare rimmed vacuoles, enlarged reactive myonuclei, with endomysial and perivascular infiltrates of chronic inflammatory cells (Figures 3 and 4).