Speedy stomata of a C 4 plant correlate with enhanced K + channel gating.

Stomata are microscopic pores at the surface of plant leaves that facilitate gaseous diffusion to support photosynthesis. The guard cells around each stoma regulate the pore aperture. Plants that carry out C 4 photosynthesis are usually more resilient than C 3 plants to stress, and their stomata operate over a lower dynamic range of CO 2 within the leaf. What makes guard cells of C 4 plants more responsive than those of C 3 plants? We used gas exchange and electrophysiology, comparing stomatal kinetics of the C 4 plant Gynandropsis gynandra and the phylogenetically related C 3 plant Arabidopsis thaliana. We found, with varying CO 2 and light, that Gynandropsis showed faster changes in stomata conductance and greater water use efficiency when compared with Arabidopsis. Electrophysiological analysis of the dominant K + channels showed that the outward-rectifying channels, responsible for K + loss during stomatal closing, were characterised by a greater maximum conductance and substantial negative shift in the voltage dependence of gating, indicating a reduced inhibition by extracellular K + and enhanced capacity for K + flux. These differences correlated with the accelerated stomata kinetics of Gynandropsis, suggesting that subtle changes in the biophysical properties of a key transporter may prove a target for future efforts to engineer C 4 stomatal kinetics.