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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.

Recent studies of the immune system of leguminous plants infected with nodular bacteria (rhizobia) are summarized. The possibility of blocking the invasion of rhizobia into plant organs not affected by the primary infection is discussed. The concept of local and systemic resistance of the leguminous plant to rhizobial infection is introduced. The Nod factors of rhizobia are considered, as well as the plant receptors that interact with these factors upon the formation of symbiosis of the plant and bacteria. The role of bacterial surface exopolysaccharides in the suppression of the protective system of the plants is discussed. The innate immunity of leguminous plant cells is assumed to affect the formation and functioning of the symbiosis of the plant and the bacteria. [ABSTRACT FROM AUTHOR]

Data from the literature and our own data on the participation and interrelation of bacterial signaling Nod-factors and components of the calcium, NADPH oxidase, and NO synthase signaling systems of a plant at the preinfection and infectious stages of the formation of a legume-rhizobium symbiosis are summarized in this review. The physiological role of Nod-factors, reactive oxygen species (ROS), calcium (Ca), NADPH oxidase, nitric oxide (NO), and their cross influence on the processes determining the formation of symbiotic structures on the roots of the host plant is discussed. [ABSTRACT FROM AUTHOR]

The effect of exogenous calcium (Ca) and rhizobial infections ( Rhizobium leguminosarum bv viceae) on the dynamics of the level of nitric oxide (NO) was studied in cross cuts of roots of two-day-old etiolated pea seedlings ( Pisum sativum L.) using a DAF-2DA fluorescent probe. Fluctuations of the NO level, indicating the presence of a rhythm in the generation of NO in roots, were observed during the incubation of seedlings in water, a CaCl solution, and with rhizobial infections. Exogenous factors (Ca and two rhizobial stamms) change the time dynamics of the NO level in comparison with the control (water). [ABSTRACT FROM AUTHOR]

Changes in the functional activity of the NADPH oxidase in the microsomal fraction of roots of etiolated pea seedlings, caused by rhizobial inoculation and calcium ions (Ca), are shown. The enzyme activity in a medium with an exogenous source of Ca (CaCl, 100 μM) fluctuated, increasing 5 to 20 min and decreasing 10 and 30 min after addition. A calcium chelator (ethylene glycol tetraacetic acid (EDTA), 100 μM) potentiated the decrease in the enzyme activity in the presence of exogenous calcium. Rhizobial inoculation caused a 3.9-fold increase in the enzyme activity 5 min after inoculation compared to the control (without inoculation). The Ca-channel activator (amiodarone, 300 μM) and the Ca-channel blocker (lanthanum chloride, 400 μM) reduced the NADPH oxidase activity after rhizobial inoculation compared to the control level (without inoculation). It is concluded that Ca and reactive oxygen species are involved in the regulation of the membrane NADPH oxidase activity in roots of pea seedlings. [ABSTRACT FROM AUTHOR]

The level of nitric oxide (NO) in roots of 2-day-old etiolated pea ( Pisum sativum L.) seedlings was investigated by fluorescence microscopy using the fluorescent probe 4,5-diaminofluorescein diacetate. Segments representing transversal (cross) cuts of the roots having thickness of 100 to 150 μm (a segment of the root located 10 to 15 mm from the apex) were analyzed. A substantial concentration of NO in the roots was registered when the seedlings were grown in water (control). Addition of 4 mM sodium nitroprusside, 20 mM KNO, 2 mM NaNO, 2 mM L-arginine into the growth medium increased NO concentration with respect to the control by 1.7- to 2.3-fold. Inhibitors of animal NO-synthase - 1 mM Nω-nitro-L-arginine methyl ester hydrochloride and 1 mM aminoguanidine hydrochloride - reduced the intensity of fluorescence in the root segments in the presence of all the studied compounds. In medium with KNO, the inhibitor of nitrate reductase −150 μM sodium tungstate -lowered the fluorescence intensity by 60%. Scavengers of nitric oxide - 100 μM 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide and 4 μM hemoglobin - lowered NO concentration in all the studied variants. Potassium ferrocyanide (4 mM) as the inactive analog of sodium nitroprusside inhibited generation of NO. These results are discussed regarding possible pathways of NO synthesis in plants. [ABSTRACT FROM AUTHOR]

The article studies the nitric oxide (NO) levels in the roots of etiolated seedlings of sowing peas ( Pisum sativum L.) using the DAF-2DA fluorescent probe and fluorescent microscopy. Cross sections of roots of 100-150 µm (the site of a root which is 10-15 mm from the apex) are analyzed. It is shown that the level of NO in the roots after 24 h increased by more than a factor of 2 in the versions with NaNO and sodium nitroprusside. At feeding the seedlings with KNO, a peak in the accumulation of NO in the roots (twofold increase) was observed after 30 min. Fertilizing seedlings with L-arginine (2 mM) increased the intensity of the fluorescence of the root sections by more than a factor of 2. The inoculation of seedlings of rhizobia ( Rhizobium leguminosarum bv. viceae) contributed to the reduction of NO on the background of the control (H2O) and sodium nitroprusside and nitrogen compounds. Scavengers of NO (2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide ( PTIO), hemoglobin) and inhibitors of nitrate reductase and animal NO synthase (sodium tungstate and aminoguanidine hydrochloride) reduced the level of NO in the roots. The results are discussed in relation to the role of NO in plants under the influence of biotic and abiotic factors. [ABSTRACT FROM AUTHOR]

Data on structural and functional characteristics of plant NADPH oxidase (Rboh) are generalized. The enzyme homologs identical to the subunit gp91 of the enzymatic complex of animal cells were found in plants. The activation of Rboh depends on the influx of Ca into the cytoplasm and phosphorylation of the N-terminal region of the enzyme by Ca-dependent protein kinase. The possibility of the involvement of Rop GTPase, a cytosolic component of Rboh, in the activation of Rboh is discussed. It is postulated that Rboh localizes on the plasma membrane of plant cells. Rboh is activated under the influence of both biotic and abiotic factors, which is apparently associated with Ca fluxes, reactive oxygen and nitrogen species, and transduction of information to the nuclear genome. [ABSTRACT FROM AUTHOR]

Published data on the role of reactive oxygen and nitrogen species (ROS and RNS, respectively) in the formation and functioning of the legume-rhizobial symbiosis are summarized. It is assumed that ROS and RNS fulfill a double function in the legume-rhizobial symbiosis by triggering the mechanisms enabling symbiosis formation and the mechanisms preventing the development of symbiotic structures (i.e., the defensive responses). A hypothetic scheme illustrating the involvement of ROS and RNS in the formation of legume-rhizobial symbiosis is proposed. [ABSTRACT FROM AUTHOR]

This review of the literature synthesizes the data on physiological mechanisms of the influence of high doses of mineral nitrogen (nitrates and ammonium) on the formation and functioning of legume-rhizobium symbiosis. The participation of phytohormonal and phenolic metabolism and active forms of oxygen and nitrogen in the symbiosis is highlighted. A close connection between these metabolic processes in the formation and functioning of legume-rhizobium symbiosis under a redundant supply of plants by mineral nitrogen is underlined. [ABSTRACT FROM AUTHOR]

H2O2 content was studied in the roots and epicotyls of pea ( Pisum sativum L.) with normal (cultivar Marat) and disturbed (non-nodulating mutant K14a and hypernodulating mutant Nod3) regulation of root nodulation after inoculation with active industrial strain of Rhizobium leguminosarum bv. viceae 250a/CIAM 1026. Pea biotypes differed by H2O2 content in roots and epicotyls. Exogenous salicylic acid (SA) (0.2 mM) affected H2O2 and SA levels in roots in an inoculation-dependent manner. The involvement of hydrogen peroxide and SA as signaling molecules as well as of antibacterial agents in the pea-rhizobium interaction at the initial stages of symbiosis is proposed. [ABSTRACT FROM AUTHOR]

Recent studies of the immune system of leguminous plants infected with nodular bacteria (rhizobia) are summarized. The possibility of blocking the invasion of rhizobia into plant organs not affected by the primary infection is discussed. The concept of local and systemic resistance of the leguminous plant to rhizobial infection is introduced. The Nod factors of rhizobia are considered, as well as the plant receptors that interact with these factors upon the formation of symbiosis of the plant and bacteria. The role of bacterial surface exopolysaccharides in the suppression of the protective system of the plants is discussed. The innate immunity of leguminous plant cells is assumed to affect the formation and functioning of the symbiosis of the plant and the bacteria.

Data from the literature and our own data on the participation and interrelation of bacterial signaling Nod-factors and components of the calcium, NADPH-oxidase, and NO-synthase signaling systems of a plant at the preinfection and infectious stages of the formation of a legume-rhizobium symbiosis are summarized in this review. The physiological role of Nod-factors, reactive oxygen species (ROS), calcium (Ca2+), NADPH-oxidase, nitric oxide (NO), and their cross influence on the processes determining the formation of symbiotic structures on the roots of the host plant is discussed.