Delimited by a membrane called tonoplast. Contains water, sugars, proteins; phenolic compounds, pigments such as betalains, anthocyanins, calcium oxalate crystals (druse, styloids, prismatic crystals, rafids, etc.) can also be found.
Many of the substances are dissolved, constituting the cellular juice, whose pH is generally acid, by the activity of a proton pump in the tonoplast.
In specialized cells a single vacuole may occur, arising from the union of small vacuoles from an old meristematic cell (stem cell); In parenchymal cells the vacuole occupies up to 90% of the cell space.
Functions: Active in metabolic processes such as:
- substance storage (small vacuoles - accumulation of proteins, ions and other metabolites). An example is the castor bean (Ricinus communis) endosperm microvacuoles, which contain aleurone grains;
- lysosomal process (Through digestive enzymes, found mainly in well-developed central vacuoles, whose tonoplast undergoes invagination to encompass organelles-containing cytoplasmic material (autophagy occurs in young cells or during senescence.) They originate from the membrane system of the Golgiense complex. Its size increases as the tonoplast incorporates Golgi complex-derived vesicles.