Dynamic behavior and internalization of aquaporins at the surface of plant cells

Abstract

Aquaporins, channel proteins that facilitate water transport across the tonoplast and the plasma membrane of plant cells, have classically been used as reference markers for these two membranes. Yet, recent studies have shown that the subcellular localization of aquaporins is constantly adjusted in response to environmental stimuli. This chapter addresses the mechanisms that determine the density at the cell surface of aquaporins of the Plasma Membrane Intrinsic Protein (PIP) subclass. While pharmacological interference coupled to confocal imaging was extensively used in initial studies, single particle tracking of PIPs fused to GFP, fluorescence correlation spectroscopy (FCS), and a novel fluorescence recovery after photobleaching approach have provided unique insights into the peculiarity of PIP cellular dynamics. It was shown in particular that, while endocytosis of PIPs is predominantly clathrin-dependent under standard conditions, PIP cycling is enhanced under salt stress possibly involving a clathrin- and membrane raft-mediated endocytosis. Future research will address the genetic bases of these pathways and their possible control by the plant hormone auxin.