Regulation of the Later Stages of Nodulation Stimulated by IPD3/CYCLOPS Transcription Factor and Cytokinin in Pea Pisum sativum L.

The IPD3/CYCLOPS transcription factor was shown to be involved in the regulation of nodule primordia development and subsequent stages of nodule differentiation. In contrast to early stages, the stages related to nodule differentiation remain less studied. Recently, we have shown that the accumulation of cytokinin at later stages may significantly impact nodule development. This conclusion was based on a comparative analysis of cytokinin localization between pea wild type and ipd3/cyclops mutants. However, the role of cytokinin at these later stages of nodulation is still far from understood. To determine a set of genes involved in the regulation of later stages of nodule development connected with infection progress, intracellular accommodation, as well as plant tissue and bacteroid differentiation, the RNA-seq analysis of pea mutant SGEFix--2 (sym33) nodules impaired in these processes compared to wild type SGE nodules was performed. To verify cytokinin’s influence on late nodule development stages, the comparative RNA-seq analysis of SGEFix--2 (sym33) mutant plants treated with cytokinin was also conducted. Findings suggest a significant role of cytokinin in the regulation of later stages of nodule development.

Response of plants and nitrogen-fixing symbiosis to the toxicity of cadmium and mercury using the pea mutant SGECdt

The combined effect of Hg and Cd on the growth, elemental composition, root exudation and interactions with rhizobia of pea SGE and its mutant SGECdt was studied in hydroponics and sand. The tolerance mechanisms of legume-rhizobia symbiosis to heavy metals are discussed.

The effect of microorganisms and heavy metals on the exudation of low molecular weight organic compounds by plant roots

The aim of our research was to study the effect of growth-promoting rhizobacteria (Pseudomonas oryzihabitans and Variovorax paradoxus) and toxic elements (Al, Cd and Hg) on the root exudation in various pea (Pisum sativum L.) genotypes. For this, methods of periodic cultures, gnotobiotic plant-microbial systems, ICPE and UPLC were used. It was established that rhizobacteria actively utilized organic acids and sugars secreted by the roots and contributed to an increase in pH and Al immobilization in the rhizosphere. Cadmium increased the exudation of many substances of pea line SGE, but this effect was more pronounced in the mutant SGECdt. Stimulation of the exudation of amino acids was detected during Hg treatment to a greater extent in wild-type SGE. The combined action of Cd and Hg did not lead to a further increase in exudation. The results obtained indicate various mechanisms of exudation of the studied fractions, while the most pronounced differences are observed between the fractions of amino acids or sugars with organic acids. Exudation of organic acids plays an important role in the decreased stability and accumulation of Hg by the pea mutant SGECdt.

Symbiosis of selected Rhizobium leguminosarum bv. viciae strains with diverse pea genotypes: effects on biological nitrogen fixation

Biological nitrogen fixation (BNF) can be improved by optimizing the interaction between the rhizobial inoculant and pea (Pisum sativum L.), leading to increased productivity and reduced nitrogen (N) fertilizer use. Eight Rhizobium leguminosarum bv. viciae strains were used to inoculate the super-nodulating pea mutant Rondo-nod3 (fix+), the hyper-nodulating pea mutant Frisson P88 Sym29, CDC Meadow commercial control, and the non-nodulating mutant Frisson P56 (nod–) to evaluate BNF in a greenhouse assay. Significant differences in strain × cultivar interactions were detected for shoot and root dry masses, which ranged from 1.8 to 4.7 g and from 0.27 to 0.73 g per plant, respectively; for nodule number on lateral roots, which ranged from 25 to 430 per plant; for amount of fixed N2, which ranged from 15 to 67 mg and from 4 to 15 mg per plant for shoot and root tissues, respectively; and for percentage of N derived from atmosphere (%Ndfa), which ranged from 37% to 61% and from 35% to 65% for shoot and root tissue, respectively. Strain × cultivar interactions in this study could contribute to identification of superior strains and pea breeding lines with genetic superiority in BNF. Nodule production in pea plants was not necessarily correlated with the amount of fixed N2, suggesting nodule activity is more important to BNF than is nodule number.