How Does Elevated CO2 Regulate the Stomatal Aperture? Is It a Balancing Act?

K.J. SHETHI, J. E. GRAY, S. CASSON
Plants, Photosynthesis and Soil, School of Bioscience, University of Sheffield, Western Bank, S10 2TN, Sheffield, UK

Stomatal aperture regulation is crucial to maintain the trade-off between opening for optimum CO2 uptake and closure to limit water loss in response to environmental stress. Therefore, the mechanisms that regulate stomatal aperture upon changes in [CO2] are a potential target for crop improvement.The interaction of multiple hormones determines stomatal aperture in a condition-specific manner. The phytohormone abscisic acid (ABA) plays a major role in regulating both stomatal closure and inhibition of opening responses. Whilst research shows that CO2 responses require the capacity for ABA biosynthesis, there is no evidence of ABA concentration changes in guard cells following changes in CO2. We propose that E[CO2] alters responses to ABA by changing the homeostasis between ABA and other phytohormones. Stomatal bioassay and mass spectrometry analysis examined these interactions and we observed gibberellins (GAs) negating the effect of ABA on the stomatal closure response to E[CO2] treatment.