Differential responses of stomatal kinetics and steady-state conductance to abscisic acid in a fern: comparison with a gymnosperm and an angiosperm.

Origins of abscisic acid (ABA)-mediated metabolic control of stomatal conductance have been suggested to be recent, based on a gradualistic model of stomatal evolution. In ferns, steady-state stomatal conductance (g ) was unresponsive to ABA in some studies, supporting this model. Stomatal kinetic responses to ABA have not been considered.