ORIGINAL ARTICLE

Phytohormones and Morphogenesis of Root Nodules and Lateral Roots of a Legume Plant

Data on the physiological role of phytohormones (mainly cytokinin and auxin) in the initiation of cortical cell division of the root, in the formation of nodule primordium and in its further organogenesis are summarized. The necessity of high level of cytokinin and low level of auxin for this process is proved. The mechanism leading to an increase in the cytokinin / auxin ratio is associated with the inhibition of auxin transport from the aerial organs to the root with the involvement of cytokinin signaling. Reducing cytokinin / auxin ratio against the background of inhibition of cytokinin signaling initiates the formation of lateral roots. The role of other phytohormones as well as flavonoids which have a positive (gibberellins, brassinosteroids) or negative influence (ethylene, abscisic, jasmonic and salicylic acids) on the formation of the root nodule is discussed. The key role of the rhizobial Nod factor signaling in the organogenesis of the nodule is emphasized. The schemes of reactions and signaling processes involved in the initiation of nodule primordium and lateral roots formation are given.