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 signalling cascade in guard cells that results in stomatal closure, thus reducing water loss 1 . ABA triggers an increase in cytosolic calcium in guard cells ([Ca 2+ ] cyt ) 2 , 3 , 4 , 5 , 6 that has been proposed to include Ca 2+ influx across the plasma membrane 3 , 5 , 7 , 8 , 9 . However, direct recordings of Ca 2+ currents have been limited 3 and the upstream activation mechanisms of plasma membrane Ca 2+ channels remain unknown. Here we report activation of Ca 2+ -permeable channels in the plasma membrane of Arabidopsis guard cells by hydrogen peroxide. The H 2 O 2 -activated Ca 2+ channels mediate both influx of Ca 2+ in protoplasts and increases in [Ca 2+ ] cyt in intact guard cells. ABA induces the production of H 2 O 2 in guard cells. If H 2 O 2 production is blocked, ABA-induced closure of stomata is inhibited. Moreover, activation of Ca 2+ channels by H 2 O 2 and ABA- and H 2 O 2 -induced stomatal closing are disrupted in the recessive ABA-insensitive mutant gca2 . These data indicate that ABA-induced H 2 O 2 production and the H 2 O 2 -activated Ca 2+ channels are important mechanisms for ABA-induced stomatal closing.