Calcium channels activated by hydrogen peroxide mediate abscisic acid signalling in guard cells

Drought is a major threat to agricultural production. Plants synthesize the hormone abscisic acid (ABA) in response to drought, triggering a signallin g cascade in guard cells that results in stomatal closure, thus reducing wa ter loss(1). ABA triggers an increase in cytosolic calcium in guard cells ( [Ca2+](cyt))(2-6) that has been proposed to include Ca2+ influx across the plasma membrane(3,5,7-9). However, direct recordings of Ca2+ currents have been limited(3) and the upstream activation mechanisms of plasma membrane C a2+ channels remain unknown. Here we report activation of Ca2+-permeable ch annels in the plasma membrane of Arabidopsis guard cells by hydrogen peroxi de. The H2O2-activated Ca2+ channels mediate both influx of Ca2+ in protopl asts and increases in [Ca2+](cyt) in intact guard cells. ABA induces the pr oduction of H2O2 in guard cells. If H2O2 production is blocked, ABA-induced closure of stomata is inhibited. Moreover, activation of Ca2+ channels by H2O2 and ABA- and H2O2-induced stomatal closing are disrupted in the recess ive ABA-insensitive mutant gca2. These data indicate that ABA-induced H2O2 production and the H2O2-activated Ca2+ channels are important mechanisms fo r ABA-induced stomatal closing.