Vacuole



A vacuole is a characteristic type of organelle found in plant and fungi cells and many single-cell organisms. The single large vacuole of the cell is surrounded by a membrane, called the tonoplast, and filled with a solution of water, dissolved ions , sugars, amino acids , and other materials.

In plants, nicotine and other toxins are stored in vacuoles, since these are as toxic to the plant as they are to the herbivores they are meant to repel. The tart juice of the orange and other citrus fruits is stored in vacuoles, as are the bright pigments that give autumn leaves their color. The vacuole also serves as waste disposal and recycling center for worn-out organelles, such as mitochondria and chloroplasts, and in this function they are similar to lysosomes in animal cells. Expansion of the vacuole by water intake is the major driving force in plant cell growth, and is also the means for maintaining cell rigidity, or turgor . To increase turgor, the tonoplast will pump ions or other material into the vacuole, causing water to infiltrate by osmosis . In a mature cell, the vacuole may occupy as much as 90 percent of the cell volume, such that the rest of the cell contents are flattened against the cell membrane.

SEE ALSO Anatomy of Plants ; Cell Wall ; Fungi ; Protista ; Secondary Metabolites in Plants ; Water Movement in Plants

Richard Robinson

Bibliography

Raven, Peter, Ray F. Evert, and Susan E. Eichhorn. Biology of Plants, 6th ed. New York: W. H. Freeman and Company, 1999.



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