CO2 sensing in stomata of abi1-1 and abi2-1 mutants of Arabidopsis thaliana

Stomatal responses to CO2 were investigated in Arabidopsis thaliana wild-type and ABA insensitive mutants (abi1-1 and abi2-1). Although stomata from abi1 and abi2 mutant plants failed to respond to ABA and were originally wide open, they still remained sensitive to illumination and atmospheric CO2-suppression, showing at least 50 %. of wild-type response. Similar results were obtained studying either stomatal movements in epidermal strip bioassays or changes in leaf conductance in whole plant experiments. The previously reported CO2 insensitivity of stomata from abi1 and abi2 mutant plants probably has to be ascribed to the experimental conditions used by the authors. Thus, in abi1 and abi2 mutant plants, total impairment in the response to ABA is accompanied by a limited inhibition in stomatal response to CO2 and light. These results do not support a total convergence of ABA and CO2 signalling pathways in guard cells.