Stopped-flow assays for measurement of water transport activity of V. vinifera aquaporins expressed in yeast.

(A) Typical traces obtained from stopped-flow spectroscopy after hyperosmotic shock. Presented signals are illustrative of ten traces at 23°C obtained from strains expressing functional (VvTnPIP2;1) and non-functional (VvTnTIP4;1) aquaporins for water transport, and control (transformed with empty plasmid pUG35). (B) Water permeability coefficients (P_f at 23°C) of VvTnPIP2;1, VvTnTIP1;1 and VvTnTIP2;2 were higher than control strain. Expression of VvTnPIP1;4, VvTnPIP2;3 and VvTnTIP4;1 did not increase water permeability in yeast cells. Data are mean ± SD of three independent experiments with at least ten traces.