ABSTRACT
In this chapter, the authors classify the existing growth retardants into three main groups: ethylene-releasing compounds, inhibitors of gibberellins (GA) translocation, and inhibitors of GAs biosynthesis. They deal with the biochemical mode of action of typical representatives of these groups. The main emphasis is being laid on inhibitors of GA biosynthesis because there is only limited new information available for the two other groups. Several compounds with a nitrogen-containing heterocycle act as inhibitors of the oxidative steps from ent-kaurene to ent-kaurenoic acid. Plant growth retardants act primarily by affecting those phytohormones that are promoting longitudinal growth: the auxins (probably via ethylene) and the gibberellins. In a given crop the usefulness of a given compound can thus also be determined by a combination of morpho-regulation with such secondary effects.
