Anion channels and hormone signalling in plant cells

Current evidences support a central role in signal transduction and turgor regulation for plasma membrane anion channels. The present review focuses on these channels as putative targets for plant hormones. Various approaches have been developed to investigate the contribution of anion channels to hormone responses at the level of integrated responses of intact cells or organs, or to study directly the hormonal regulation of anion channels at the membrane level. These approaches are mainly discussed for two biological models, stomatal guard cells and hypocotyl or coleoptile cells, both cell types being equipped with several types of anion channels. Membrane potential and anion flux measurements, together with pharmacological studies using anion channel inhibitors, reveal that anion permeabilities are involved in the responses of guard cells or hypocotyl cells to abscisic acid and/or auxin. In a few instances, a modulation of anion channel activity can be detected in voltage-clamp or patch-clamp experiments. From these data and other studies, anion channel activation seems to constitute a very early step in many transduction cascades within response pathways to endogenous hormonal signals, but also to abiotic and biotic environmental signals such as light or molecules involved in plant-pathogen interactions. This points to plasma membrane anion channels as major actors in plant signalling networks.