Plant plasma membrane water channels conduct the signalling molecule H2O2

Abstract

H2O2 is a relatively long-lived reactive oxygen species that signals between cells and organisms. H2O2 signalling in plants is essential for response to stress, defence against pathogens and the regulation of programmed cell death. Although H2O2 diffusion across membranes is often considered as a passive property of lipid bilayers, native membranes represent significant barriers for H2O2. In the present study we addressed the question of whether channels might facilitate H2O2 conduction across plasma membranes. The expression of several plant plasma membrane aquaporins in yeast, including PIP2;1 from Arabidopsis (where PIP is plasma membrane intrinsic protein), enhanced the toxicity of H2O2 and increased the fluorescence of dye-loaded yeast when exposed to H2O2. The sensitivity of aquaporin-expressing yeast to H2O2 was altered by mutations that alter gating and the selectivity of the aquaporins. The conduction of water, H2O2 and urea was compared, using molecular dynamics simulations based on the crystal structure of SoPIP2;1 from spinach. The calculations identify differences in the conduction between the substrates and reveal channel residues critically involved in H2O2 conduction. The results of the calculations on tetramers and monomers are in agreement with the biochemical data. Taken together, the results strongly suggest that plasma membrane aquaporin pores determine the efficiency of H2O2 signalling between cells. Aquaporins are present in most species and their capacity to facilitate the diffusion of H2O2 may be of physiological significance in many organisms and particularly in communication between different species.