Hormones in Plants Bearing Nitrogen-fixing Root Nodules: Distribution and Seasonal Changes in Levels of Cytokinins in Alnus glutinosa (L.) Gaertn

The root nodules of both dormant and non-dormant plants of Alnusglutinosa (L.) Gaertn. were found (by the soybean callus bioassay)to contain levels of cytokinin activity greatly exceeding thoseof other parts of young vegetative plants. A large, transient increase in cytokinin activity occurred inthe nodules at the time of bud break. Similar, although muchsmaller, increases were detected also in roots and buds. Theincrease in the level of nodule cytokinin activity was observedboth in mature trees and in young pot-grown plants in two successiveyears. A second peak of cytokinin activity, considered to bederived from cytokinin nucleotides, was found in the nodulesof mature trees in midsummer. Analysis of cytokinin extracts of different plant parts by meansof a Sephadex LH20 column revealed the presence of three mainpeaks of activity, with elution volumes corresponding to thoseof zeatin-9-glucoside, zeatin riboside, and zeatin. While theglucoside-like peak -was predominant in the nodules and leavesit was not detected in root pressure sap. A zeatin ribo-side-likepeak was the major cytokinin in the roots and root pressuresap. These findings are discussed in relation to current hypothesesconcerning the production, distribution, and possible physiologicalroles of the cytokinins.