The role of roots in the enhancement of
cytokinin content and leaf growth of Phaseolus vulgaris plants after
decapitation and partial defoliation was investigated. Partial excision of the roots of plants which were decapitated above the primary leaf node resulted in a reduction of leaf growth and soluble
proteins accumulation in the primary leaves. Roots excision was done at time of
decapitation and repeated 8 days later. Endogenous
cytokinins, known to be involved in enhancing shoot growth, accumulated in the leaves and stems of decapitated and partially defoliated plants. Lower levels of
cytokinins were detected in the leaves of decapitated plants with only a partial root system. The level of
cytokinins in the roots of decapitated plants was reduced by partial root excision. The growth and accumulation of
cytokinins in leaves were, however, not totally suppressed by removing a large proportion of the roots. At the commencement of the experiment the stem had a higher
cytokinin content than both the leaves and roots. This suggests that the stem could be an alternative source of
cytokinins to the leaves. The
cytokinin complement in the leaves of decapitated plants is not identical to that in the roots. It appears that
cytokinins supplied by the roots are metabolized in the leaves, or that alternatively certain
cytokinins are synthesized in the leaves themselves.