Aquaporins facilitate the transport of water and small neutral solutes across cell membranes. Tonoplast. A number of isoforms are produced. According to EST sequences. Predominantly expressed in developing seeds. Also expressed in rosette leaves. 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.