Two potential Ca2+-mobilising processes depend on the abscisic acid concentration and growth temperature in the Arabidopsis stomatal guard cell

The abscisic acid (ABA) stomatal closing signal might be transduced through different pathways, depending on the plant growth temperature (GT) and the applied ABA concentration. This was investigated in epidermal peels of Arabidopsis thaliana (L.) Columbia. Different Ca2+ buffers and guanosine-triphosphate-binding protein (G protein) modulators were tested on stomatal closing under light in response to 3 mumol/L ABA (ABA(3mu)) and 30 mumol/L ABA (ABA(30mu)) at the 15-17degreesC and 23-25 degreesC GT ranges. The Ca2+ buffer, 1,2-bis(O-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, used, as free acid (BAPTA) or acetoxymethyl ester (BAPTA-AM), similarly inhibited (Up to approximately 70% inhibition) stomatal closing to ABA(3mu) and ABA(30mu), whereas ethylene glycol-bis(beta-aminoethyl ether)N, N,N,N',N'-tetraacetic acid specifically inhibited (up to approximately 70% inhibition) the ABA(3mu) response at the 23-25 degreesC GT range. At the same GT range, the ABA(3mu) response was specifically affected by the phospholipase C (PLC) inhibitor 1-[6-[[17beta-3-methoxyestra-1,3,5(10)-trien-17-yl] amino] hexyl]-1H-pyrrole-2,5-dione (U73122). Moreover, the ABA(30mu) response was specifically inhibited by the G protein antagonist pGlu-Gln-D-Trp-Phe-D-Trp-D-Trp-Met-NH2 (GP Ant-2) and by the inactive mastoparan analog, mas17. The inhibitory effects of GP Ant-2 and mas17 were additive. None of the tested pharmacological compounds were effective at the 15-17degreesC GT range. Together, these results confirmed that, depending on GT and the exogenous ABA concentration, stomatal closing to ABA involves either one among two Call mobilisations or none of them.