Speedy stomata of a C₄ 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 C₄ photosynthesis are usually more resilient than C₃ plants to stress, and their stomata operate over a lower dynamic range of CO₂ within the leaf. What makes guard cells of C₄ plants more responsive than those of C₃ plants? We used gas exchange and electrophysiology, comparing stomatal kinetics of the C₄ plant Gynandropsis gynandra and the phylogenetically related C₃ plant Arabidopsis thaliana. We found, with varying CO₂ 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 C₄ stomatal kinetics.