Aquaporin required to facilitate the transport of water from the vacuolar compartment to the cytoplasm. Does not promote glycerol permeability. Its function is impaired by Hg(2+). Transports urea in yeast cells and Xenopus laevis oocytes in a pH-independent manner. Transports methylammonium or ammonium in yeast cells and Xenopus laevis oocytes, preferentially at high medium pH. May participate in vacuolar compartmentation and detoxification of ammonium. Interacts with cucumber mosaic virus (CMV) Protein 1a. Tonoplast. It is specifically located in the tonoplast of protein storage vacuoles (PSV) (By similarity). Strongly expressed in shoot, rosette, bolt and flowers. Also expressed in roots, flower buds and above ground. Starts to be expressed in seedlings from 2 days ays after germination. By ammonium nitrate in roots. Expressed in roots with a circadian rhythm showing an increase after onset of light, a peak approximately at midday and a decline to lowest levels before offset of light. Aquaporins contain two tandem repeats each containing three membrane-spanning domains and a pore-forming loop with the signature motif Asn-Pro-Ala (NPA). Belongs to the MIP/aquaporin (TC 1.A.8) family. TIP (TC 1.A.8.10) subfamily. Was originally assigned as At3g16230, which is now a completely different protein not related to aquaporins.