Plant hormones are known to have pleiotropic effects on growth and development. For example, the naturally occurring auxin, IAA, influences cell division, cell elongation, and differentiation. A variety of early events (time scale: seconds to hours) preceding the biological response to auxin has been described (Brummell and Hall, 1987). However, the specificity of these early responses and their significance for the occurrence of the biological response are in general far from clear. For instance, the stimulation of proton extrusion and the hyperpolarization of the plasma membrane potential are well-described rapid auxin effects. Recently, however, it was shown that both growth-promoting auxins and growth-inactive structural analogs were capable of inducing these processes (Felle et al., 1991; Peters and Felle, 1991), demonstrating that stimulation of the proton pump is a rather unspecific effect of auxin, although the activation of the H+-ATPase is indispensable for the occurrence of cell elongation.During the past few years, a number of research groups, including our own, have studied early effects of auxins on the induction of specific proteins and mRNAs (for recent reviews, see Guilfoyle, 1986;Theologis, 1986; Key, 1989).