Flower stalk segments of Arabidopsis thaliana ecotype Columbia lack the capacity to grow in response to exogenously applied auxin

Exogenously applied IAA stimulated cell elongation of segments excised from flower stalks of Arabidopsis thaliana ecotype Landsberg erecta (Ler) by in creasing the cell wall extensibility, but it did not affect that of ecotype Columbia (Col), Treatment with a low pH buffer solution (pH 4.0) or fusico ccin (FC), a reagent activating H+-ATPases, significantly increased the cel l wall extensibility and promoted elongation growth of flower stalk segment s of both ecotypes, indicating that the flower stalk segments of Col posses s the capacity to grow under acidic pH conditions. IAA promoted the proton excretion in segments of Ler but not of Col, On the other hand, FC increase d the proton excretion in segments of Col as much as that of Ler. These res ults suggest that IAA activates the plasma membrane H+-ATPases in the segme nts of Ler but not those of Col, while FC activates them in both ecotypes, Flower stalks of Col may lack the mechanisms of activation by IAA of the pl asma membrane H+-ATPases.