Hormones in Plants Bearing Actinomycete Nodules

Abstract

Bioassay of chromatographic fractions of extracts of the perennial nodules of Alnus glutinosa indicates that the levels of cytokinins and gibberellin-like substances undergo seasonal fluctuations and that the highest levels occur prior to the recommencement of nitrogen fixation in the spring. A comparison of the cytokinin activity of nodulated alders and nonnodulated alders fertilized with nitrogen showed that the only consistent difference between the two sets of plants was the higher percentage of cytokinin activity in the leaves of nonnodulated plants, which was probably related to their consistently better root development. Most of the nodule cytokinin activity occurred as a glucoside of zeatin, suggesting that nodule cells normally store rather than export any excess of cytokinin.