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 o n these channels as putative targets for plant hormones. Various approaches have been developed to investigate the contribution of anion channels to h ormone responses at the level of integrated responses of intact cells or or gans, or to study directly the hormonal regulation of anion channels at the membrane level. These approaches are mainly discussed for two biological m odels, stomatal guard cells and hypocotyl or coleoptile cells, both cell ty pes being equipped with several types of anion channels. Membrane potential and anion flux measurements, together with pharmacological studies using a nion channel inhibitors, reveal that anion permeabilities are involved in t he responses of guard cells or hypocotyl cells to abscisic acid and/or auxi n. In a few instances, a modulation of anion channel activity can be detect ed in voltage-clamp or patch-clamp experiments. From these data and other s tudies, anion channel activation seems to constitute a very early step in m any transduction cascades within response pathways to endogenous hormonal s ignals, 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. (C) Elsevier, Paris.