Abstract
The plasma and vacuolar membrane aquaporins play a key role in the intercellular and intracellular water transport in plants. In radish, among the six isoforms of RsPIPs and two isoforms of RsTIPs, the levels of mRNA of RsPIP2-1, RsPIP2-2 and RsPIP2-3 and of RsPIP2-1 protein were varied with the organ and the stage of growth, and were responsive to water stresses and phytohormones (Suga et al. 2001, 2002). The protein levels of the RsPIP1 group and RsTIPs on a membrane protein basis were retained at a relatively constant level. We investigated the water transport activity of each radish aquaporins. Radish aquaporins were expressed individually in the yeast (BJ5459), and then water channel activity were assayed using a stopped-flow spectrophotometer. RsPIP2s and RsTIPs exhibited water transport activity, however that of RsPIP1s were undetectable. We will discuss about the physiological function.
