Jonas Chaves Alvim

1 INTRODUCTION In C3 plants the photosynthetic efficiency (ratio of carboxylation to oxygenation) decreases rapidly at high temperatures (Laing et al., 1974) and periods of drought because the stomatal closure limits the CO2 uptake (Simpson et al., 2022). C4 metabolism is one of the CO2-concentrating mechanisms that has evolved to increase the concentration of CO2 at the active site of Rubisco (Hatch, 1971; Hatch & Slack, 1966).

Abstract Stomata of plant leaves open to enable CO2 entry for photosynthesis and close when CO2 in the leaf is elevated. CO2 is thought to promote stomatal closure in part by activating the SLAC1 anion channel at the guard cell plasma membrane. Carbonic anhydrases (CAs) contribute to this activation, but their contribution as distinct from CO2-H2CO3 catalysis remains controversial.