May function as water channel to facilitate the transport of water across cell membrane. Expressed in roots, leaves and anthers. Down-regulated by osmotic stress, chilling, drought and treatment with gibberellin and abscisic acid (ABA). Increased expression in the recovery (post-stress) phase of gibberellin and abscisic acid treatment or drought. Aquaporins contain two tandem repeats each containing three membrane-spanning domains and a pore-forming loop with the signature motif Asn-Pro-Ala (NPA). Recovery of PIP1.1 expression after chilling is increased by pretreatment with mannitol. Belongs to the MIP/aquaporin (TC 1.A.8) family. PIP (TC 1.A.8.11) subfamily.