ABA-mediated regulation of stomatal density is OST1-independent (Plant Direct)

Stomata are not only important for CO2 uptake, but are also important in limiting water loss when the water availability is running low. Stress hormone ABA activates protein kinase OPEN STOMATA 1 (OST1) leading to opening of ion channels, water efflux and stomatal closure. Increased levels of ABA decrease the stomata density in ABA over-accumulating mutant lines (cyp707a1/a3). By combining mutations in ABA sensitivity with defects in ABA biosynthesis or breakdown Jalakas et al. observed that ABA-deficiency leads to wider stomatal opening, while ABA overaccumulation has no effect on the aperture width. The ABA-sensitivity had no effect on the stomatal density, suggesting a separation of stomatal aperture regulation from stomatal development, which might be a useful tool in breeding programs. (Summary by Magdalena Julkowska) Plant Direct 10.1002/pld3.82