Effects of abscisic acid on the soluble RNA polymerase activity in maize coleoptiles

Effects of abscisic acid (ABA) on the polymerase activity have been investigated. The specific activity of the RNA polymerase enzyme decreased when coleoptiles were preincubated for 6 hours or longer in 3.8×10(-5)M ABA. Inhibition of RNA synthesis could however already be detected after 3 hours ABA treatment.Inclusion of (RS) cis-trans ABA in the grinding medium decreased the polymerase activity; inclusion of (RS) trans-trans ABA in the medium only had a small effect on the activity. Addition of (RS) cis-trans and (RS) trans-trans ABA to the RNA polymerase assay system also gave a slight inhibition of activity.The strong inhibition when (RS) cis-trans ABA was included in the grinding medium indicates that the hormone interacts with an activator molecule which is not present in the partly purified RNA polymerase solution.It is suggested that ABA may have more than one mode of action.