[The NADPH oxidase activity of pea seedling roots in rhizobial infection depending on abiotic and biotic factors].

The changes in NADPH activity was studied in the roots of 3-4-day-old etiolated pea (cultivar Aksaiskii usatyi) seedlings depending on plant inoculation with Rhizobium leguminosarum bv. viceae (strain CIAM 1026), adverse environmental factors (low temperature and high dose of a mineral nitrogen fertilizer), chemical substances (sodium nitroprusside and methyl viologen, or paraquat), and a biotic factor--the bacterium Escherichia coli (strain XL-1 Blue). It was demonstrated that all exogenous factors increased the activity of microsomal NADPH oxidase. Rhizobial infection removed the activation caused by exogenous factors only in the case of high nitrogen content in the medium, thereby displaying an antagonistic effect. A synergistic action on the enzyme activity was observed in the variants with combined action of rhizobia + paraquat and rhizobia + E. coli. An increased NADPH oxidase activity coincided with a growth inhibition of pea seedling roots. The results are discussed from the standpoint of the roles of NADPH oxidase and reactive oxygen species in the legume-rhizobium symbiosis.