Stimulus‐induced downregulation of root water transport involves reactive oxygen species‐activated cell signalling and plasma membrane intrinsic protein internalization

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Abstract
The water uptake capacity of plant roots (i.e. their hydraulic conductivity, Lpr) is determined in large part by aquaporins of the plasma membrane intrinsic protein (PIP) subfamily. In the present work, we investigated two stimuli, salicylic acid (SA) and salt, because of their ability to induce an accumulation of reactive oxygen species (ROS) and an inhibition of Lpr concomitantly in the roots of Arabidopsis plants. The inhibition of Lpr by SA was partially counteracted by preventing the accumulation of hydrogen peroxide (H2O2) with exogenous catalase. In addition, exogenous H2O2 was able to reduce Lpr by up to 90% in 2O2 on the activity of individual aquaporins in Xenopus oocytes, and on a pharmacological dissection of the action of H2O2 on Lpr, we propose that ROS do not gate Arabidopsis root aquaporins through a direct oxidative mechanism, but rather act through cell signalling mechanisms. Expression in transgenic roots of PIP-GFP fusions and immunogold labelling indicated that external H2O2 enhanced, in 2O2-induced internalization of PIPs, to downregulate root water transport.