Abstract
Stomata, small pores on the surfaces of leaves formed by a pair of guard cells, adapt rapidly to changes in the environment by adjusting the aperture width. As a long‐term response, the number of stomata is regulated during stomatal development. The hormone abscisic acid (ABA) regulates both processes. In ABA mediated guard cell signaling the protein kinase OPEN STOMATA1 (OST1) has a central role, as stomatal closure in the ost1 mutant is impaired in response to ABA and to different environmental stimuli. We aimed to dissect the contribution of different ABA‐related regulatory mechanisms in determining stomatal conductance, a combination of stomatal density and aperture width, and crossed the ost1 mutant with mutants that either decreased (aba3) or increased (cyp707a1/a3) the concentration of ABA in plants. The double mutant ost1 aba3 had higher stomatal conductance than either parent due to a combination of increased stomatal aperture width and higher stomatal density. In the triple mutant ost1 cyp707a1/a3, stomatal conductance was significantly lower compared to ost1‐3 due to lower stomatal density. Further characterization of the single, double and triple mutants showed that responses to treatments that lead to stomatal closure were impaired in ost1 as well as ost1 aba3 and ost1 cyp707a1/a3 mutants, supporting a critical role for OST1 in stomatal aperture regulation. On the basis of our results, we suggest that two signaling pathways regulate water flux from leaves, that is, stomatal conductance: an ABA‐dependent pathway that determines stomatal density independent of OST1; and an OST1‐dependent pathway that regulates rapid changes in stomatal aperture.
Highlights
Stomata, formed by a pair of guard cells, are small pores responsible for gas exchange in leaves
Aperture of ost1 cyp707a1/a3 was similar to ost1-3, whereas ost1 aba3 had significantly wider aperture compared to the single mutants (Figure 2b)
These results suggest that abscisic acid (ABA)‐deficiency leads to wider stomatal apertures, whereas over‐accumulation of ABA seems to have no effect on aperture width
Summary
Stomata, formed by a pair of guard cells, are small pores responsible for gas exchange in leaves. They allow CO2 uptake for photosynthesis, with the accompanying loss of water. Accurate adjustment of the stomatal pore is required for the plant to successfully thrive in a changing environment. The width of the stomatal aperture, and the number of stomata is regulated by environmental signals and influences plant gas exchange (Hetherington & Woodward, 2003). Several studies have shown that doubling of ambient CO2 concentration leads to a reduction in stomatal
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