When the transporter is knocked out from guard cell vacuoles there is a significant reduction in malate flow current. The current goes from a huge inward current to not much different than the WT, and Meyer et al hypothesized that this is due to residual malate concentrations in the vacuole.
When the transporter is absent from guard cell vacuoles, there's a substantial decrease in malate flow current. The current shifts from an extremely large inward current to nearly identical to WT, and Meyer et al. proposed that this is due to residual malate concentrations within the vacuole.