Résumé
The current climate change associated to elevated CO2 is directly impacting on plant development. Environmental CO2 directly acts on leaf transpiration, regulating stomatal aperture. Stomata are pores on the surface of land plants, delimited by two guard cells, and regulate gas exchanges. Stomatal aperture is key for determining CO2 uptake and, simultaneously, water loss by transpiration. Therefore, it is finely modulated by environmental factors. To regulate the stomatal aperture, guard cells undergo a regulated swelling and shrinking mechanism that depends on ion fluxes across the plasma membrane (PM) and the vacuolar membrane (VM). The transport systems residing in these membranes and mediating such ion fluxes need coordination. Ion channels of the ALMT family localized in the plasma and the vacuolar membranes are important actors of the guard cell responses. Specifically, both the VM channel ALMT4 and the PM channel ALMT12 are involved in stomatal closure. We generated double knock-out lines almt4-almt12 and we measured the stomatal conductance and net photosynthesis rate upon application of ABA and high CO2 concentration. Our data show that ALMT12 function dominates the induction of stomatal closure after ABA treatment. Notably, we found that in response to increased CO2, ALMT4 and ALMT12 are likely to work in synergy to drive stomatal closure. Our findings highlight the importance of the interplay between the PM and the VM ion channels in stomatal responses