Membrane transport and Ca²⁺ oscillations in guard cells

Since the 1980s, work on ion transport and the control of guard cell ion channels has provided a wealth of information that is still unparalleled in plant biology, driven primarily by electrophysiological studies and, more recently, by molecular genetics and cell biology. We know now sufficient detail of all of the major transport pathways at the plasma membrane to encapsulate these fully with accurate kinetics and flux equations in which all of the key parameters are constrained by experimental data. Both experimental and modelling (so-called systems biology) approaches have already yielded important insights into oscillatory signal interactions, especially in relation to Ca²⁺?and Ca²⁺-dependent signal processing. Critical to understanding these events is a recognition of the capacity for feedback that is inherent to ion transport across a single membrane, and embodied in the common intermediates of ion concentrations and membrane voltage. Here, we review this background and its relevance to Ca2signals and oscillations that have been demonstrated to occur in guard cells, and we place this evidence in context to support that short-term oscillations in solute transport are the norm for homeostatic control of osmotic content.