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Abstract Stomatal opening in the light, observed in nearly all vascular land plants, is essential for providing access to atmospheric CO2 for photosynthesis. The speed of stomatal opening in the light is critical for maximizing carbon gain in environments in which light intensity changes, yet we have little understanding of how other environmental signals, particularly evaporative demand driven by vapor pressure deficit (VPD) influences the kinetics of this response. In angiosperms, and some fern species from the family Marsileaceae, a mechanical interaction between the guard cells and the epidermal cells determines the aperture of the pore. Here, we examine whether this mechanical interaction influences the speed of stomatal opening in the light. To test this, we investigated the speed of stomatal opening in response to light across a range of VPDs in seven plant species spanning the evolutionary diversity of guard cell and epidermal cell mechanical interactions. We found that stomatal opening speed is a function of evaporative demand in angiosperm species and Marsilea, which have guard cell and epidermal cell mechanical interactions. Stomatal opening speeds did not change across a range of VPD in species of gymnosperm and fern, which do not have guard cell mechanical interactions with the epidermis. We find that guard cell and epidermal cell mechanical interactions may play a key role in regulating stomatal responsiveness to light. These results provide valuable insight into the adaptive relevance of mechanical advantage.
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This content will become publicly available on May 21, 2026
The Protein Kinase Inhibitor, Tyrphostin AG126, and Its Derivatives Suppress Phosphorylation of Plasma Membrane H+-ATPase and Light-Induced Stomatal Opening
Abstract Phosphorylation of the penultimate residue, threonine (pen-Thr), of plasma membrane (PM) H+-ATPase is essential for its activation and blue light (BL)-induced stomatal opening. However, the regulatory mechanism of action of PM H+-ATPase pen-Thr phosphorylation is not completely understood. Here, we performed screening using a protein kinase inhibitor library and found that tyrphostin AG126 inhibited phosphorylation of PM H+-ATPase pen-Thr in guard cells in response to light and fungal toxin fusicoccin (FC), in addition to inhibition of light- and FC-induced stomatal opening. Analysis of the structure–activity relationship using AG126 derivatives revealed the hydroxyl group at the C-5 position of the compound to be essential for its activity. We further characterized one AG126 derivative, AGD-1, which effectively suppressed BL-induced stomatal opening with a half-inhibitory concentration of 2.0 μM. AGD-1 inhibited PM H+-ATPase pen-Thr phosphorylation in guard cells in response to BL and FC. In addition, AGD-1 suppressed FC-induced PM H+-ATPase pen-Thr phosphorylation in mesophyll cell protoplasts, implying that the effect of AGD-1 is not specific to guard cells. Furthermore, to improve the permeability of AGD-1, we synthesized acetylated AGD-1 (AcAGD-1), which was found to suppress BL- and FC-induced stomatal opening. AcAGD-1 suppressed light-induced PM H+-ATPase pen-Thr phosphorylation, but not Thr881 phosphorylation, in leaf discs, which is important for guard cell PM H+-ATPase activation in addition to pen-Thr phosphorylation. This study identified a novel stomatal opening inhibitor capable of specifically inhibiting PM H+-ATPase pen-Thr phosphorylation.
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- Award ID(s):
- 2434687
- PAR ID:
- 10598994
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Plant And Cell Physiology
- ISSN:
- 0032-0781
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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