what is tonoplast and what is its role?
Answers
Tonoplasts are nothing like what their name would suggest (unless you know Greek). A tonoplastis actually the membrane that surrounds the large vacuole in a mature plant cell. We get the name 'tonoplast' from Greek, which translated looks something like 'tone, tension, stretching, and molded.' This would coincide well with where the tonoplast exists. It is also known as the 'vacuolar membrane.'
A vacuole is basically an organelle that is filled with food and/or waste particles. They are used to take in certain food substrates and then dissolve them. A large vacuole can make up around 95% (in some plants) of the plant cell and is rather unique to plants. Also called the central vacuole, its main job is to maintain turgor pressure inside of the plant. Turgor pressure helps the plant keep its shape by pressing the plasma membrane against the cell wall. This maintains a nice, rigid structure for the plant. Think about nice, crisp lettuce versus old, wilt-y looking lettuce. This is the best example of turgor pressure.
The membrane that surrounds the vacuole is the tonoplast. The name makes sense now, as we see the name means 'tension' and the tonoplast keeps tension on the vacuole. This helps to give the vacuole some form of structure. It also helps to maintain proper balance of nutrients and ions inside and out of the vacuole, thus keeping proper turgor pressure in the plant cell.