Plant aquaporins: their molecular biology, biophysics and significance forplant water relations

Over the last decade, considerable advances have occurred in understanding the molecular biology and biophysics of water permeation across plant membr anes and tissues. Spurred on by the rapid advances in cloning and functiona l characterization of a superfamily of major intrinsic proteins, some of wh ich function as aquaporins, the biophysics of transport of water and small non-electrolytes across plant membranes is being re-examined based on the p roposed function of these membrane-integral proteins in their native membra nes. This review focuses on a number of issues that are central to an under standing of aquaporin function: (1) the need to be able to test for water-c hannel activity in native membranes; (2) the implications of the observed s olute/water selectivity of aquaporins; (3) the putative functional roles of aquaporins at the cell, tissue and organ levels in plants; and (4) informa tion that can be obtained from studies of the abundance, diversity and expr ession patterns of aquaporins. It is clear that to answer many of the criti cal questions that remain concerning aquaporin function, combined studies u sing appropriate molecular and biophysical techniques will be required.