The tonoplast is a membrane that surrounds the vacuole, or organelle that is present in the cells of plants and fungi. The tonoplast is also known as the vacuolar membrane.
The tonoplast is a stretchy membrane, and its main function is to protect the vacuole and isolate it from harmful substances. The tonoplast membrane controls ionic movement in and around the cell. Water flowing in and out of the vacuole is regulated by the tonoplast. Some animal and bacterial cells also contain vacuoles that are bound by vacuolar membranes. The size and structure of the vacuole varies depending on the cell.