Water channel required to facilitate the transport of water across cell membrane. Essential for the water permeability of the plasma membrane and for the morphology of the root system. Its function is impaired by Hg(2+). Inhibited by cytosolic acidosis which occurs during anoxia in roots. A number of isoforms are produced. According to EST sequences. Widely expressed. Expressed in roots and above ground. By blue light and abscisic acid (ABA). 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. PIP (TC 1.A.8.11) subfamily.