title: Ca(2+)-activated anion channels and membrane depolarizations induced by blue light and cold in Arabidopsis seedlings.
abstract: The activation of an anion channel in the plasma membrane of Arabidopsis thaliana hypocotyls by blue light (BL) is believed to be a signal-transducing event leading to growth inhibition. Here we report that the open probability of this particular anion channel depends on cytoplasmic Ca2+ ([Ca2+]cyt) within the concentration range of 1 to 10 microM, raising the possibility that BL activates the anion channel by increasing [Ca2+]cyt. Arabidopsis seedlings cytoplasmically expressing aequorin were generated to test this possibility. Aequorin luminescence did not increase during or after BL, providing evidence that Ca2+ does not play a second-messenger role in the activation of anion channels. However, cold shock simultaneously triggered a large increase in [Ca2+]cyt and a 110-mV transient depolarization of the plasma membrane. A blocker of the anion channel, 5-nitro-2-(3-phenylpropylamino)-benzoic acid, blocked 61% of the cold-induced depolarization without affecting the increase in [Ca2+]cyt. These data led us to propose that cold shock opens Ca2+ channels at the plasma membrane, allowing an inward, depolarizing Ca2+ current. The resulting large increase in [Ca2+]cyt activates the anion channel, which further depolarizes the membrane. Although an increase in [Ca2+]cyt may activate anion channels in response to cold, it appears that BL does so via a Ca(2+)-independent pathway.
authors.affiliation: Department of Botany, University of Wisconsin, Madison 53706, USA.
authors.forename: B D
authors.initials: BD
authors.lastname: Lewis
authors.forename: G
authors.initials: G
authors.lastname: Karlin-Neumann
authors.forename: R W
authors.initials: RW
authors.lastname: Davis
authors.forename: E P
authors.initials: EP
authors.lastname: Spalding
mesh_terms: D000331:Aequorin / Q000235:genetics / Q000378:metabolism; D000838:Anions; D017360:Arabidopsis / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D003080:Cold Temperature; D007473:Ion Channels / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000528:radiation effects*; D008027:Light; D008564:Membrane Potentials / Q000528:radiation effects*; D009579:Nitrobenzoates / Q000494:pharmacology; D030821:Plants, Genetically Modified; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D000838:Anions; D007473:Ion Channels; D009579:Nitrobenzoates; D011994:Recombinant Proteins; C058176:5-nitro-2-(3-phenylpropylamino)benzoic acid; D000331:Aequorin; D002118:Calcium