Pharmacological study of two potential Ca2+ signalling pathways within stomatal closing in response to abscisic acid in Commelina communis L.

It has been previously suggested that, depending on its applied concentration, abscisic acid (ABA) induces stomatal closing through one of two potential Ca2+-dependent transduction pathways. This hypothesis was worked further in Commelina communis by comparing the stomatal responses to 10 nM ABA (ABA(10)) and 100 nM ABA (ABA(100)) on the basis of a pharmacological dissection of implicated Ca2+ signalling. Compared to the ABA(10) response, the response to ABA(100) was differentially affected by the putative plant modulators of Ca2+ fluxes caffeine, ruthenium red, procaine, SDZ-202 791 S(+), S-(-)-BAY K8644 and SDZ-202 791 R(-). Furthermore, the ABA(100) response specifically displayed positive interactions between the plant Ca2+ buffer 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) and the anion channel blockers anthracene-9-carboxylic acid, [(6,7-dichloro-2-cyclopentenyl-2,3-dihydro-2-methyl-1-oxo-1H-inden-5-yl)oxy]acetic acid or 2-(alpha,alpha,alpha-trifluoro-m-toluidine)-pyridine-3-carboxylic acid, whereas the anion channel blocker 5-nitro-2,3-phenylpropyllamine benzoic acid positively interacted with BAPTA to prevent both the ABA,, and ABA,,, responses. Together, these results might support indirectly that stomatal closing in a graded response to increasing concentrations of exogenous ABA proceeds from different Ca2+ signalling pathways. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.