Carbonic Anhydrase Mutants in Have Altered Stomatal Responses to Environmental Signals.

Stomata regulate transpirational water loss and CO uptake for photosynthesis in response to changing environmental conditions. Research investigating stomatal movement has mostly been conducted in C eudicot species, which have very different CO requirements for photosynthesis relative to C grasses. Carbonic anhydrase (CA) catalyzes the hydration of CO, and its activity has been linked to stomatal aperture regulation in eudicots. The number of genes and their evolutionary history differ between monocots and dicots, and many questions remain unanswered about potential neofunctionalization and subfunctionalization of grass paralogs and their roles in photosynthesis and stomatal conductance. To investigate the roles of different genes in maize (), we examined stomatal responses in and single mutants as well as a double mutant. The and single mutants had 10% and 87% of the CA activity exhibited by the wild type, respectively, while had less than 5% of wild-type CA activity. The mutants had higher stomatal conductance than the wild type and slower stomatal closure in response to increases in CO partial pressure. Contrary to previous reports in eudicots, mutants showed slowed stomatal closure in response to the light-dark transition and did not show differences in stomatal density compared with the wild type. These results implicate CA-mediated signaling in the control of stomatal movement but not stomatal development. Drought experiments with mutant plants suggest a role for CA in water-use efficiency and reveal that is not optimized for water-use efficiency under well-watered conditions.