Leaf apoplastic pH signatures govern responses to salt stress in V. faba guard cells

Philipp Meyer and Christoph-Martin Geilfus
Department of Soil Science and Plant Nutrition, Hochschule Geisenheim University, Von-Lade-Straße 1, 65366, Geisenheim, Germany.

Changes in stomatal cavity pH are crucial for stomatal function in response to environmental cues. This study investigates transient salinity-induced apoplastic pH (pHapo) increases in Vicia faba stomatal cavities, analyzing downstream effects via GC transcriptomics and proteomics. Employing spatiotemporal real-time pHapo quantification, NaCl-induced pHapo transients were imaged in the leaf and GC apoplast. To isolate pHapo effects from salt-ion effects, artificially induced pHapo shifts with a MOPSO buffer at pH 6.5 were investigated alongside NaCl-induced alkalinization. Proteomic analysis identified 20 proteins in GC linked to decreased proton concentration, including HSP70, pectin acetylesterase, and EDGP, essential for stress response and cell wall stabilization. Transcriptomic analysis revealed 17 pHapo-responsive transcripts in GC, highlighting beta-1,3-galactosyltransferase and integrin-linked kinase 1, a negative stress regulator. The common functions of the identified proteins and transcripts likely enhance GC resilience under environmental stress, aiding cell wall stabilization and stress-responsive signaling. This study provides insights into how GC perceive environmental cues through proton concentration changes in the leaf apoplast and the resulting downstream responses in the GC symplast.