Disentangling the role of sucrose for stomatal movement regulation

The role of sucrose for stomatal movement regulation has long been debated, with several controversial studies and theories. Here we demonstrated that sucrose concentration at the leaf apoplast underpin the diel course of tobacco stomatal conductance (gs), in which the daily stomatal opening and closure were associated with low and high concentration of apoplastic sucrose, respectively. In agreement with this, exogenously applied sucrose increased the speediness of both stomatal opening and closure in a concentration-dependent manner. We further showed that the light-induced stomatal opening is closely associated to the dynamic of sucrose and organic acids within guard cells. Interestingly, these sucrose-mediated stomatal responses were drastically reduced in plants with diminished capacity to import sucrose to their guard cells, highlighting that sucrose importation to these cells is important to modulate the magnitude of both stomatal opening and closure. Modelling analysis highlights that the metabolism of the apoplast rather than the leaf is the major determinant of the daily gs. Our results collectively indicate that sucrose is a master regulator of the daily gs, being capable of inducing and accelerating both stomatal opening and closure in a concentration and location of accumulation dependent manner.