The Stomatal Response to Reduced Relative Humidity Requires Guard Cell-Autonomous ABA Synthesis

Abstract

Stomata are pores on the leaf surface, bounded by two guard cells, which control the uptake of CO(2) for photosynthesis and the concomitant loss of water vapor. In 1898, Francis Darwin showed that stomata close in response to reduced atmospheric relative humidity (rh); however, our understanding of the signaling pathway responsible for coupling changes in rh to alterations in stomatal aperture is fragmentary. The results presented here highlight the primacy of abscisic acid (ABA) in the stomatal response to drying air. We show that guard cells possess the entire ABA biosynthesis pathway and that it appears upregulated by positive feedback by ABA. When wild-type Arabidopsis and the ABA-deficient mutant aba3-1 were exposed to reductions in rh, the aba3-1 mutant wilted, whereas the wild-type did not. However, when aba3-1 plants, in which ABA synthesis had been specifically rescued in guard cells, were challenged with dry air, they did not wilt. These data indicate that guard cell-autonomous ABA synthesis is required for and is sufficient for stomatal closure in response to low rh. Guard cell-autonomous ABA synthesis allows the plant to tailor leaf gas exchange exquisitely to suit the prevailing environmental conditions.

Fern Stomatal Responses to ABA and CO2 Depend on Species and Growth Conditions

“…1C). This could be explained by increased ABA levels induced by low air humidity, as observed in other species (Bauer et al, 2013;McAdam and Brodribb, 2015), which could potentially lead to partial ABA-induced closure of the stomata of ferns grown in the growth room and no further effect of ABA treatment on stomatal conductance. If the ABA response is already activated in ferns grown at lower RH, these plants would be expected to have lower stomatal conductance.…”

“…These data suggest a greater flexibility and faster stomatal responsiveness to changes in vapor pressure deficit (VPD) in angiosperms. This could be expected, as the responses to changes in VPD are linked with the biosynthesis and presence of ABA (Bauer et al, 2013;McAdam and Brodribb, 2015) as well as ABA signaling (Merilo et al, 2013), and stomatal ABA responses in angiosperms are faster and stronger than in ferns (Brodribb and McAdam, 2011; Fig. 1, B and C).…”

“…This experiment indicates that there is more than just a passive mechanism that regulates the stomatal response to a change in VPD in this fern species. As ABA and the components of its signaling pathway mediate stomatal responses to changes in VPD in angiosperms (Bauer et al, 2013;Merilo et al, 2013;McAdam and Brodribb, 2015) and A. filix-femina is a fern with ABA-responsive stomata (Fig. 1C), ABA is an obvious candidate as a mediator of stomatal response to high VPD in A. filix-femina.…”

An Integrated Hydraulic-Hormonal Model of Conifer Stomata Predicts Water Stress Dynamics

“…Until recently, little was known about the time dynamics for ABA biosynthesis, even though early studies suggested the water potential trigger for ABA synthesis occurred when leaf turgor approached zero Raschke, 1980, 1981). The role of guard cell biosynthesis of ABA in responses to humidity is also unclear (Bauer et al, 2013). However, by providing a way to predict the effect of constant leaf [ABA] on stomatal conductance on the backbone of a hydraulic model, the model here provides an important stepping stone for working toward a dynamic model including both water relations and ABA dynamics.…”

The spatio-temporal specificity of PYR1/PYL/RCAR ABA receptors in response to developmental and environmental cues

“…11 It is well known that osmotic stress-derived ABA can reduce leaf hydraulic conductivity and shoot growth, thus reducing the transpiration rate in Arabidopsis leaves, [12][13][14] whereas it can maintain root water uptake by enhancing root growth and root hydraulic conductivity. 8,11,[15][16][17] Recently it is found that the single PYL8 ABA receptor play a key role in mediating ABA-controlled root growth and root response to moisture gradient, means hydrotropism, [17][18] while there is a obvious redundant characteristics of PYR1/PYL/RCAR ABA receptor family in stomatal aperture regulation.…”