Today, there is concern about how to improve farming practices in areas subject to drought. It is essential to understand the mechanisms underlying drought resistance and effective plant water use so as to adapt to changes in global climate. In plants, the majority of water loss occurs via pores on the leaf surface, called stomata. The degree of stomatic pore opening varies and controls the rate of water vapor diffusion by the plant. In addition to controlling water loss, the stomata also allow the required influx of CO₂ into the leaf for photosynthesis. Thus, the main challenge of the stomata is to optimize CO₂ capture while limiting excessive water loss.

Stomata are also a potential gateway for pathogens. Abscisic acid (ABA), the key hormone in the plant response to water deficiency, triggers, via the production of hydrogen peroxide (H₂O₂), signaling processes that lead to stomatic closure.

Aquaporins (AQP) are proteins that form channels that promote the passage of water molecules through cell membranes in higher plants. Until now, their role has been very hypothetical. To learn more about them, researchers from the CNRS and the INRA in Montpellier, in collaboration with the Biam and the Nara Institute of Science and Technology (Japan), showed that plants lacking the gene encoding the AQP protein PIP2;1 present a stomatic closure defect in response to water stress and release of the ABA hormone. Nevertheless, these plants show normal responses to darkness, light and CO₂. The use of a H₂O₂-sensitive fluorescent probe (HyPer) revealed the accumulation of H₂O₂ in wild plants in response to the ABA hormone. This accumulation is abolished in mutant plants.

"This work provides the first direct genetic and physiological evidence of a role for aquaporins in stomatic movements", explains Nathalie Leonhardt, a researcher at the Biam. "It allows us to propose that PIP2;1 simultaneously plays hydraulic and signaling roles, by facilitating the transport of water and H₂O₂ across the cell membrane". This study also provides essential knowledge for engineering more drought-tolerant plants.