Effects of Kinetin and Other Plant Growth Regulators on Starch Degradation

Abstract

IT has been known since the work of Hayashi¹ that gibberellins stimulate the activity of amylase in germinating barley and wheat grains. This work has been extended by Paleg^2–4, who has reported an increase in the activity of both α- and β-amylases in barley endosperm following treatment with gibberellic acid (GA₃). So far as we are aware this communication is the first to suggest that kinetin may also play a part in starch degradation. This effect of kinetin was first suspected when young excised wheat coleoptiles treated with solutions of gibberellic acid and kinetin⁵ were stained with iodine. Starch was found to be present in the control coleoptiles whereas in those treated with the two growth regulators no starch was detectable. Estimations of reducing sugars in extracts of these coleoptiles, after treatment, also demonstrated that the growth response promoted by these two growth regulators was accompanied by starch breakdown (Table 1). When excised coleoptiles were grown in D-glucose solution alone the starch remained and yet the maximal growth response was as great as with kinetin. These results thus indicated that the growth responses induced by GA₃ and kinetin in young coleoptiles could be explained, at least in part, simply in terms of the liberation of D-glucose. Indolyl-3-acetic acid produced no measurable effect on growth or starch breakdown (Table 1).