Aquaporins and water homeostasis in plants

Aquaporins are water channel proteins of vacuolar and plasma membranes. Whe n opened they facilitate the passive movement of water molecules down a wat er potential gradient. In Arabidopsis, 30 genes have been found that code f or aquaporin homologues. Some of these genes code for highly abundant const itutively expressed proteins and some are known to be temporally and spatia lly regulated during development and in response to stress. The water trans port activity of two aquaporins is regulated at the protein level by phosph orylation and dephosphorylation. At a given time, cells express several dif ferent aquaporins, and it is probable that vacuolar and plasma membrane aqu aporins acting in concert are responsible for the cytosolic osmoregulation that is necessary for maintaining normal metabolic processes. inhibition st udies of aquaporins in vivo and antisense mutant studies suggest that, in a ddition to cytosolic osmoregulation, aquaporins are important for the bulk flow of water in plants.