Identification of an H O permeable PIP aquaporin in barley and a serine residue promoting H O transport.

A barley (Hordeum vulgare) plasma membrane type aquaporin, HvPIP2;5, was identified as an H O permeable aquaporin among 21 barley and rice PIPs examined in the heterologous expression system using Saccharomyces cerevisiae. Four TIPs were also detected as H O -transporting aquaporins among 15 barley and rice TIPs. Influx of H O into yeast cells expressing HvPIP2;5 was determined with a florescent-dye-based assay. Indirect immunofluorescence indicated that the expression of HvPIP2;5 protein was ubiquitous in root tissues, and was also weakly observed in leaf epidermal cells and cells in the vascular bundle. Point mutated variants of HvPIP2;5 were generated by the site-directed mutagenesis. Growth assays of yeast cells expressing these mutated HvPIP2;5 proteins suggested that Ser-126 in HvPIP2;5 has a large impact on H O transport with a minor influence on the HvPIP2;5-mediated water transport.