Expression of a single‐chain Fv antibody against abscisic acid creates a wilty phenotype in transgenic tobacco

The plant hormone abscisic acid (ABA) participates in the control of several important physiological processes in plants such as stomata regulation, seed dormancy and stress tolerance. A new strategy was developed to study these phenomena by blocking abscisic acid with intracellularly expressed specific single‐chain variable fragment (scFv) antibodies. Here evidence is presented that the expression of single‐chain Fv antibodies against abscisic acid in the endoplasmic reticulum of transgenic tobacco cells leads to a wilty phenotype. Stomatal conductance is increased at high CO2 concentrations dependent on the level of antibody expression in leaves. Symptoms of abscisic acid deficiency were generated in the transformants although they have even higher levels of abscisic acid than wild‐type plants.