Kinetin antagonizes the inhibition of auxin synthesis in the Avena coleoptile caused by galactose, abscisic acid or indoleacetic acid

The degree of inhibition of the auxin production in the tip of a decapitated Avena coleoptile, caused by galactose at low concentrations (0.10 and 0.125%) is reduced by kinetin (1 mg/1), but not by gibberellic acid (GA ,, 10 mg/1). At higher galactose concentrations the reduction is insignificant or absent. The inhibiting effect of galactose on the cell elongation due to external auxin is not reversed by kinetin. Comparable effects of kinetin are observed when the auxin production and the auxin action are inhibited by abscisic acid. Kinetin also abolishes the repression of the auxin production caused by indoleacetic acid itself, but this effect is limited to very low IAA concentrations (0.01 mg/1). When the inhibition is caused by 0.02 mg/1 IAA the effect of kinetin added in concentrations of 1, 5 or 10 mg/1 is already absent.