Plant Aquaporins: Roles in Water Homeostasis, Nutrition, and Signaling Processes
Exchange across biological membranes is controlled by the composition of the lipid bilayer, diffusion-facilitating channels, and active transport proteins. In 1992, a protein facilitating the passive diffusion of water across membranes was discovered in humans and named aquaporin-1. Since then, an increasing number of proteins belonging to the same superfamily of membrane intrinsic proteins have been identified and characterized as ubiquitous indispensable players in transmembrane water fluxes and water homeostasis. Compared to all other kingdoms of life, plants possess a high number of isoforms, clustered into seven subfamilies. A fascinating diversity of small, water-soluble, and uncharged compounds, ranging from gases to metalloids, has been identified as substrates for plant aquaporins. This chapter summarizes a variety of features and transport properties of these membrane pores illustrating their physiologically crucial contribution to water homeostasis, nutrition, and signaling processes.