Spollen, W.G., Department of Agronomy, Plant Science Unit, University of Missouri, Columbia, MO 65211, United States
Lenoble, M.E., Department of Agronomy, Plant Science Unit, University of Missouri, Columbia, MO 65211, United States
Samuels, T.D., Department of Agronomy, Plant Science Unit, University of Missouri, Columbia, MO 65211, United States
Bernstein, N., Department of Agronomy, Plant Science Unit, University of Missouri, Columbia, MO 65211, United States
Sharp, R.E., Department of Agronomy, Plant Science Unit, University of Missouri, Columbia, MO 65211, United States

Previous work showed that primary root elongation in maize (Zea mays L.) seedlings at low water potentials (ψ(w)) requires the accumulation of abscisic acid (ABA) (R.E. Sharp, Y. Wu, G.S. Voetberg, I.N. Saab, M.E. LeNoble [1994] J Exp Bot 45: 1743-1751). The objective of the present study was to determine whether the inhibition of elongation in ABA-deficient roots is attributable to ethylene. At a ψ(w) of -1.6 MPa, inhibition of root elongation in dark-grown seedlings treated with fluridone to impose ABA deficiency was largely prevented with two inhibitors of ethylene synthesis (aminooxyacetic acid and aminoethoxyvinylglycine) and one inhibitor of ethylene action (silver thiosulfate). The fluridone treatment caused an increase in the rate of ethylene evolution from intact seedlings. This effect was completely prevented with aminooxyacetic acid and also when ABA was supplied at a concentration that restored the ABA content of the root elongation zone and the root elongation rate. Consistent results were obtained when ABA deficiency was imposed using the vp5 mutant. Both fluridone-treated and vp5 roots exhibited additional morphological symptoms of excess ethylene. The results demonstrate that an important role of ABA accumulation in the maintenance of root elongation at low ψ(w) is to restrict ethylene production.