Cytokinin and auxin participation in nodulation process regulation in legumes

The article summarizes the data on physiological role of phytohormones - cytokinin and auxin - in initiation of root cortical cells division resulting in formation of root nodule primordium and its further organogenesis. High level of cytokinin and low level of auxin have been proven to be a prerequisite for this process. The mechanism providing the increase in cytokinin : auxin ratio is linked to inhibiting auxin transport from aerial organs to the root with the involvement of cytokinin signaling. Decrease in cytokinin : auxin ratio at the background of inhibiting cytokinin signaling initiates formation of lateral roots. Alternative role of rhizobial Nod-factor, cytokinin and flavonoids in root nodule organogenesis is discussed. Schemes of reactions and compounds participating in initiating of nodule primordium and lateral roots formation are presented.