The involvement of the root apex and cytokinins in the control of lateral root emergence in lettuce seedlings

Removal of the apical 3 mm of the primary root of hydroponically-grown lettuce seedlings 3 or 5 days after sowing, prevented further elongation of the root and increased both the number and total length of lateral roots. The length of the lateral zone, i.e. the distance from the base of the parent root to the lateral nearest the tip, except on one occasion, remained the same as the control in both 3 and 5 day treatments, until the length of the decapitated root (which had ceased elongating) became limiting.Zeatin applied via the roots, at a concentration range from 3 × 10^–10 M to 10^–8 M reduced tap root extension growth at all concentrations. Lateral root emergence was enhanced by low zeatin concentrations and retarded by higher ones. In general, the lateral zone length was the same in cytokinin-treated plants as in untreated controls.