Vacuoles are large membrane-bound compartments within some eukaryotic cells and can serve different purposes, such as capturing food materials or unwanted structural debris surrounding the cell, sequestering materials that might be toxic to cells, maintaining fluid balance (called turgor) within the cell, exporting unwanted substances from the cell, and even determining relative cell size. Examples of vacuoles that perform these functions are described below.
Most mature plant cells have a central vacuole, which often takes up more than 90% of the cell interior. It is surrounded by a membrane and is called the tonoplast. The tonoplast actually serves many different purposes; these are:
- Storage of organic compounds, proteins (in seeds), and inorganic ions (e.g., K+ and Cl-).
- Separation of toxic byproducts from cell metabolism.
- Storage of pigments (e.g., red and blue pigments in flowers).
- Protection of the plant tissue from predation by storing toxic compounds.
- Contributing to cell growth by absorbing water (e.g., cell elongation).
- Allowing some plant cells to reach considerable size.