Transporters in fruit vacuoles

The vacuole is by far the largest organelle in fruits and can occupy more than 90 percent of the cell volume. Therefore, if we eat fruits and their products, we mainly eat the compounds stored within the vacuole. The main compounds are sugars, organic acids and secondary metabolites, such as phenolics and terpenoids, that are important for fruit quality. High concentrations of sugars, organic acids and inorganic ions in fruits generate a high osmotic pressure leading to a strong negative water potential that attracts water, allowing the fruit to grow. Accumulation of solutes within the vacuole requires many transporters in the vacuolar membrane, which is also called tonoplast. This review summarizes studies of transporters in fruit vacuoles, including proton pumps, aquaporins, sugar transporters, organic acid transporters and ABC transporters.