From salt stress to guard cell gene expression and response: Leaf apoplastic pH as a mediator

This study investigates the role of the leaf apoplastic pH in regulating stress responses in broad bean (Vicia faba) guard cells (GC) under salinity stress. Using ratiometric microscopy, changes in leaf apoplastic pH (pHapo) were quantified and linked to molecular responses in GCs, including gene expression, protein abundance, ion concentrations, and phytohormone levels. Apoplastic alkalinisation, induced by salt stress and artificial means, triggered stress-responsive molecular mechanisms in GCs. Notably, the accumulation of extracellular dermal glycoproteins (EDGPs) and retrotransposon-related transcripts was observed, suggesting a strong connection between leaf pHapo shifts and stress adaptation. These findings emphasise the regulatory role of pHapo in GCs, indicating its potential for modulating plant stress responses. The study provides valuable insights into the role of pH-sensitive mediation of pathways that enhance plant resilience to environmental stress.