Herbicides are widely used in agricultural production to protect plants, including legumes. It is known that herbicides can have a negative effect on legume-rhizobial symbiosis. In this study, the effect of the systemic herbicide Sprut Extra (glyphosate) and selective systemic herbicide Forward (quizalofop-P-ethyl) on the structural organization of pea (Pisum sativum L.) nodules was investigated. The plants were treated in concentrations: recommended by the manufacturer, twofold for both herbicides, fivefold for Sprut Extra, and tenfold for Forward. Both herbicides had no effect on the growth of pea plants (except for the variant treated with Sprut Extra before inoculation). The nodules also showed no visible changes, except for the variant treated with a fivefold concentration of Sprut Extra. At the ultrastructural level, herbicides caused cell wall deformations, accumulation of poly-β-hydroxybutyrate in bacteroids, expansion of peribacteroid space in symbiosomes, and chromatin condensation. The abnormalities were more pronounced after treatment of plants with Sprut Extra. Transcriptome analysis revealed upregulation of expression of a number of histone genes in nodules after the Sprut Extra treatment. In general, both herbicides caused little change in nodule morphology when used at the recommended doses. However, the selective herbicide Forward is more environmentally friendly for symbiotic nodules and its use in agricultural production seems preferable.
