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A possible physiological mechanism of legume-Rhizobium symbiosis, consisting in regulation of the intensity of oxidation processes by the microsymbiont in response to infection with Rhizobium, was analyzed using our own and published data. The results used in the analysis included data on the content of reactive oxygen species (O2*-, and H2O2), activity of antioxidant enzymes (superoxide dismutase, catalase, and peroxidase), and intensity of lipid peroxidation proceeding with the involvement of lipophilic phenolic compounds of the microsymbiont.

The changes in the contents of protein and free amino acids in pea plants inoculated with Rhizobium leguminosarum were studied taking into account the susceptibility of roots to root nodule bacteria. The content of cytoplasmic protein during infection increased in the actively growing root region (0-5 mm) and decreased in the root regions susceptible to rhizobia (5-20 mm from the root tip). The quantitative composition of free amino acids changed essentially upon inoculation of pea seedlings with R. leguminosarum.

The response to the action of exogenous IAA and BAP was studied and nodulation was monitored in the rhizobia-susceptible region of the root of pea seedlings (Pisum sativum L.). The pro/antioxidant activities of "soluble" and ionic and covalently bound peroxidases to the cell walls, the content of soluble phenolic compounds (PCs) extracted with ethyl acetate, their antiradical activity with DPPH, the content of PCs bound to cell walls, and the content of salicylic acid (SA) were the reaction indicators. Etiolated pea seedlings grown in a thermostat with a temperature of 21°C in cuvettes on wet filter paper were used for the study. The roots of the original 2-day-old seedlings were marked at a distance of 5–20 mm from its tip (the zone susceptible to rhizobia), and the seedlings were simultaneously inoculated with the bacteria Rhizobium leguminosarum bv. viceae and treated with solutions of 10–11M IAA and 10–9 M BAP. The movement of the marked area was monitored after 24 h. It was excised for biochemical studies, and cytological indicators that characterize the features of growth processes under the action of exogenous phytohormones (PCs) were calculated for the apical part of the root adjacent to the marked area of the root. Some of the seedlings inoculated and exposed to PCs were left to control their nodulation. The action of exogenous PCs led to increased root growth and displacement compared to the control (inoculated roots without PC treatment), the zone susceptible to rhizobia, and to a slight increase in its length. The displacement occurred due to increased elongation of the cells (IAA) that had again switched to this process and increased cell division of the meristem (BAP). Nodulation in the observation area was carried out and even increased under the action of BAP, but it was inhibited under the action of IAA. The presented biochemical parameters suggest that the manifestations of defense reactions in the studied root zone are significantly higher in the variant with IAA, which may explain the negative effect of exogenous IAA on nodulation. [ABSTRACT FROM AUTHOR]

A possible physiological mechanism of legume- Rhizobium symbiosis, consisting in regulation of the intensity of oxidative processes by the macrosymbiont in response to infection with Rhizobium, was analyzed using our own and published data. The results used in the analysis included data on the content of reactive oxygen species (O and H2O2), activity of antioxidant enzymes (superoxide dismutase, catalase, and peroxidase), and intensity of lipid peroxidation proceeding with the involvement of lipophilic phenolic compounds of the microsymbiont. [ABSTRACT FROM AUTHOR]

The changes in the contents of protein and free amino acids in pea plants inoculated with Rhizobium leguminosarum were studied taking into account the susceptibility of roots to root nodule bacteria. The content of cytoplasmic protein during infection increased in the actively growing root zone (0–5 mm) and decreased in the root zones susceptible to rhizobia (5–20 mm from the root tip). The quantitative composition of free amino acids changed essentially upon inoculation of pea seedlings with R. leguminosarum. [ABSTRACT FROM AUTHOR]