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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.

Data on the role of the legume-rhizobial symbiosis (LRS) in national economic and a brief history of the fundamental study of this unique biological phenomenon are summarized. The features of the formation of root nodules of determinant and indeterminant types are described. The physiological role of the rhizobial Nod factor in suppressing the defense system of a legume plant and the role of the plant's immune systems (MTI and ETI) in the rhizobial infection and the formation of LRS are discussed. Signal systems of a legume plant (Ca2+, NO-synthase, NADPH oxidase) and their components (ROS, RNS) and other signaling molecules involved and interacting in LRS onset are described. The necessity of studying the local and systemic resistsnce of the legume plant to the rhizobial infection is emphasized.

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.

Studied time dynamics (during 60 mines) a level oxide nitric (NO) in cross cuts of roots 2 – day etiolated seedlings of pea sowing (Pisum sativum L.) by use of fluorescent probe DAF-2DA and a fluorescent microscope depending on action exogenous calcium (Ca2+). During an exposition of seedlings on water, solution CaCl2 are shown fluctuation in level NO in roots – his increase and decrease that testifies to the certain rhythm in generation NO. Exogenous factors (Ca2+) change time dynamics of level NO in comparison with variant “water”. Ca2+chelate EGTA removes action exogenous calcium on rhythmical change of a level NO in roots. Results are discussed in aspect of close interference of signaling systems and molecules (Ca2+, NO, Н2О2).

The data on the influence of different concentration of sodium nitroprusside (SNP), potassium nitrate (KNO3), sodium nitrite (NaNO2) and L-arginine on 3 days-old etiolated pea seedlings growth and nitric oxide (NO) content in roots of these seedlings are obtained. It is found that 24 h exposition of seedlings to SNP showed negative influence on growth at a 4 mM dose; SNP at 0.05 mM doze stimulates their growth and 0.1 mM doze did not influence on seedlings growth. Using KNO3 negative influence on growth at the same exposition was showed only at superhigh concentration – 20 mM. Using NaNO2 negative influence on growth was shown at a doze of 2 mM but concentration of 0.1 and 0.5 mM did not influence on it. The exposition of seedlings to L-arginine caused growth inhibition already at concentration of 0.5 mM and reached maximum at 4 mM doze. Determination of NO level in roots using fluorescent probe DAF-2DA in variants with the greatest growth inhibition has showed, that the maximal inhibition of growth in roots and highest level of NO in roots in variants with SNP (4 mM) and NaNO2 (2 mM) was observed. In variants with KNO3 (20 mM) and L-arginine (4 mM) maximal growth inhibition did not coincide with NO accumulation and was observed after 30 min after the beginning of plants exposition and further it was reduced in 24 h. Results are discussed in connection with possible influence NO and participation of the investigated connections in generation nitric oxide in roots of pea seedlings.

Literature data on the physiological role of calcium (Ca2+) in legume-rhizobium symbiosis development on initial stages - the infection and symbiotic structures formation, are generalized. The questions about the Ca2+ function in plants, special feature the formation of legume-rhizobium symbiosis and role of calcium in the interaction of two organisms are considered. Data on the interaction of ROS and Ca2+ in the development of the legume-rhizobium symbiosis and the relationship of NADPH-oxidase activity with the calcium signaling system are analyzed. The special attention is given to the role of Ca22+-spiking and calcium and calmodulin-like kinase in the initiation of plant symbiotic ways operation leads to infection and the formation of symbiotic structures.

In article the literary data on a physiological role nitric oxide (NO) at vegetative organisms are generalized. Multifunctionality NO at the various organisms, caused by high reactionism of this molecule, its ability to react with proteins and low-molecular substances is emphasized. Questions of participation NO in various physiological processes, possible mechanisms of synthesis NO at plants, interaction with others endogenous molecules, and also the mechanisms preventing toxic effect nitric oxide are considered.