Vakuolin

Vakuolin is the Finnish term for the vacuole, a membrane-bound organelle present in many eukaryotic cells. In plants and fungi the vacuole can occupy a large portion of the cell and is bounded by a specialized membrane called the tonoplast. The vacuolar lumen contains water and a mixture of dissolved ions, sugars, organic acids, pigments, and sometimes enzymes or waste products.

Functions include maintaining turgor pressure for cell rigidity and growth, storage of ions and metabolites, sequestration of toxic compounds, and degradation of macromolecules through vacuolar hydrolases. Vacuoles participate in osmoregulation and pH balance and can serve as reservoirs for nutrients and pigments such as anthocyanins.

Types and occurrences: central vacuoles are characteristic of plant and many fungal cells; contractile vacuoles occur in some protists to expel excess water; food vacuoles form during phagocytosis; lysosome-like vacuoles are functional equivalents to animal lysosomes in some cells.

Formation and dynamics: vacuoles originate from vesicles derived from the endoplasmic reticulum and Golgi apparatus, with enlargement via fusion and water uptake through aquaporins. Their size and content can change with developmental stage and environmental conditions.

See also: Vacuole, Tonoplast, Plant cell, Fungal cell.