Abstract
A. thaliana contains 35 members of aquaporin family (PIP, TIP, NIP, and SIP). For understanding of function and physiological role of each member, we carried out a series of experiments on aquaporins in A. thaliana and radish. Here we will discuss the following findings. (i) We heterologously expressed each aquaporin in yeast and determined the water channel activity by stopped-flow spectrophotometry. There was no marked difference in the activity between TIP and PIP2 members. (ii) The PIP2 members showed high water channel activity, but the PIP1 members did not. (iii) A characteristic residue of the PIP2 subfamily (Val-235) is essential for water channel function. Replacement of this residue to Ile, which is common in PIP1s, resulted in inactivation. (iv) Both microscopic observation of GFP-fusion proteins and subcellular fractionations revealed the ER membrane localization of SIP members. These observations indicate the diversity of aquaporin members in function and physiological role.
