Functional lack of SLAC1 modifies guard cell metabolism without impacting photosynthesis under elevated [CO2] and moderated water restriction

Abstract

Understanding stomatal response to fluctuations in atmospheric carbon dioxide concentration ([CO₂]) and water deficit is important to predict the overall plant performance under these two major environmental stressing factors. In Arabidopsis, slow-type anion channel (SLAC1) plays a central role in the control of stomatal closure with impacts on water use efficiency. Here we investigated whether the stomatal component also plays a central role in limiting photosynthesis in plants showing constitutive higher stomatal conductance (g_s), such as slac1 mutants, under high CO₂ levels and water restriction. Under these conditions, slac1 plants showed similar photosynthetic performance and growth when compared to wild-type (WT) plants. Furthermore, our results suggest that the constitutive increased stomatal aperture in slac1 plants is associated with a reorganization of primary metabolism in guard cells, in addition to the ion transport impairment, previously observed in slac1 mutants. Altogether, our results indicate that higher g_s in slac1 plants are not translated into enhanced photosynthetic performance and growth, independently of CO₂ levels and watering conditions.