<P> Large vacuoles are found in three genera of filamentous sulfur bacteria, the Thioploca, Beggiatoa and Thiomargarita . The cytosol is extremely reduced in these genera and the vacuole can occupy between 40--98% of the cell . The vacuole contains high concentrations of nitrate ions and is therefore thought to be a storage organelle . </P> <P> Gas vacuoles, which are freely permeable to gas, are present in some species of Cyanobacteria . They allow the bacteria to control their buoyancy . </P> <P> Most mature plant cells have one large vacuole that typically occupies more than 30% of the cell's volume, and that can occupy as much as 80% of the volume for certain cell types and conditions . Strands of cytoplasm often run through the vacuole . </P> <P> A vacuole is surrounded by a membrane called the tonoplast (word origin: Gk tón (os) + - o -, meaning "stretching", "tension", "tone" + comb . form repr . Gk plastós formed, molded) and filled with cell sap . Also called the vacuolar membrane, the tonoplast is the cytoplasmic membrane surrounding a vacuole, separating the vacuolar contents from the cell's cytoplasm . As a membrane, it is mainly involved in regulating the movements of ions around the cell, and isolating materials that might be harmful or a threat to the cell . </P>

What is the vacuoles function in a plant cell