Cytosolic water potential as a mechanistic driver of leaf airspace unsaturation and non-stomatal control of transpiration

Abstract

1Mesophyll cells exhibit a previously underappreciated capacity to regulate water loss via low plasma membrane conductance (Lp), offering a non-stomatal mechanism for transpiration control. However, the structural basis and regulation of Lp remain poorly understood, limiting its integration into predictive models. In this study, we show that Lp responds dynamically to changes in cytosolic water potential ({psi}cy), decreasing as{psi} cy approaches the turgor loss point. This identifies{psi} cy as the primary physiological signal regulating Lp. We introduce a predictive, physiologically grounded model linking Lp to{psi} cy. Our model establishes a mechanistic connection between internal water status, leaf hydraulics, substomatal cavity unsaturation, and gas exchange. This framework opens new avenues for understanding and modelling plant water use under stress.