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Phytohormones, Rhizobium Mutants, and Nodulation in Legumes ¹

V. Cytokinin Metabolism in Effective and Ineffective Pea Root Nodules

Research School of Biological Sciences, Australian National University, Canberra, A. C., T., Australia 2601

[³H]Zeatin riboside was supplied to intact pea (Pisum sativum) plants either onto the leaves or onto the root nodules. When applied directly to nodules, approximately 70% of recovered radioactivity remained in the nodules, approximately 15% was detected in the root system, and 15% was in the shoot. However, when supplied to the leaves, little ³H was transported, with approximately 0.05% of recovered radioactivity being found in the root system and nodules. On a fresh weight basis, nodules accumulated more ³H than the parent root. In both types of studies, metabolites with an intact zeatin moiety were detected in root nodules.

In all experiments, two-dimensional thin layer chromatography revealed that little ³H remained as zeatin riboside in root or nodule tissue at the end of the labeling period. Nodules metabolized [³H]zeatin riboside to the following cytokinins/cytokinin metabolites: zeatin, adenosine, adenine, the O-glucosides of zeatin and zeatin riboside, lupinic acid, nucleotides of adenine and zeatin, and the dihydro derivatives of many of these compounds.

Although a few small differences were observed, there were no major differences between root and nodule tissue in their metabolism of [³H] zeatin riboside. Furthermore, any differences between effective and ineffective nodules were generally minor.

¹ Supported in part by an Agrigenetics-sponsored research program.