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

Aquaporin structure–function relationships: Water flow through plant living cells

“…Many more MIP family genes have since been identified in plants, with additional members in Arabidopsis, tobacco, spinach, tomato, the ice plant (Mesembryanthemum crystallinum), radish, and snapdragon [2,3,9]. The permeability values establish limits on aquaporin tissue densities required for physiological function and suggest significant structural and functional differences among the aquaporins [10].…”

“…The other aspect is the discovery that some aquaporins are multifunctional channel proteins, allowing some small neutral solutes across cellular membranes, such as glycerol, CO 2 , ammonia (NH 3 ), urea, boron, and hydrogen peroxide [13][14][15][16][17]. The diversity of aquaporin isoforms in plants can also be explained in part by their presence in multiple subcellular compartments [7,9,18].…”

“…Discovery of the aquaporin family of water channel proteins has provided a molecular explanation for rapid water movements across the plasma membranes of cells while diffusion still works in parallel [9,26,28]. This may be one reason for the abundance and diversity of aquaporins, in particular in plants.…”

“…Further investigation is necessary to determine the atomic structure of the water pore and the mechanism of its selectivity [5,64,66]. Moreover, the specificity of more plant aquaporins also needs to be determined, and plausible plant metabolites need to be tested, in order to identify regions important to specificity [5,9,20,32].…”

“…Regulation of aquaporin trafficking may also represent a way to modulate membrane water permeability, and the factors affecting and regulating aquaporin behaviors possibly involve phosphorylation, heteromerization, pH, Ca 2+ , pressure, solute gradients and temperature drought, flooding and so on (Fig. 3), which suggests aquaporins are involved in a versatile and dynamic regulation of water movement [1][2][3]5,9,20,32,50]. The abundance and activity of aquaporins in the plasma membrane and tonoplast may be regulated, hence enabling the plant to tightly control water fluxes into and out of its cells, as well as within the cells [5,6,19,50].…”