Cytokinin production in relation to the development of pea root nodules

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Abstract
Quantitative changes in cytokinins were examined in developing root nodules on the lateral roots of seedlings of the garden pea Pisum sativum cv. Little Marvel infected with Rhizobium leguminosarum strain 128 C53.Cytokinin activity was highest in 2- and 3-week-old nodules, when the growth rate was high, and decreased in older nodules. The cytokinin activities of 3-week-old nodules of various sizes were positively correlated with mitotic indices. In 3- and 4-week-old nodules most of the cytokinins were present in the white meristematic tip and not in the infected nitrogen-fixing or senescent cells. Since high cytokinin levels were associated with nodules having high mitotic rates or with the meristematic cells, it is proposed that cytokinins influence nodule morphogenesis by regulating the mitotic activity of the nodule meristem.