Oxidative stress in the root nodules of Phaseolus vulgaris is induced under conditions of phosphorus deficiency

One of the most adverse effects of phosphorus (P) deficiency on N₂-fixing legumes is the generation of harmful active oxygen species which cause oxidative stress. And although oxidative stress has been widely studied in roots and shoots of various plant species, it has not yet sufficiently been documented in bean nodules so far. In this study, two recombinant inbred lines RIL115 (P-deficiency tolerant) and RIL147 (P-deficiency sensitive) of common bean and Concesa (local variety) were inoculated separately with the reference strain R. tropici CIAT899, RhM₁₁ (R. gallicum) or RhM₁₄ (R. tropici); two local strains of the Marrakesh region of Morocco. Nodulated plants were grown under semi-hydroponic conditions with sufficient or deficient P supply and analyzed for their oxidative responses at the flowering stage. The results indicated that P-deficiency decreased the growth of shoots (48 %) and nodules (32 %), particularly with RhM₁₄ exhibiting the highest decrease (52 %) of nodulation. This constraint increased electrolyte leakage of nodules (40 %) as compared to leaves (20 %), especially for plants inoculated with RhM₁₄ and CIAT899. Moreover, high H₂O₂ and malondialdehyde contents were noticed in P-deficient nodules of RhM₁₄ and RhM₁₁. These variations were associated with peroxidase activity stimulation in P-deficient nodules induced by CIAT899 and RhM₁₄. In symbiosis with RIL115, these last strains exhibited the highest nodule phenol content. Overall, phenol content was mainly enhanced in P-deficient nodules (35 %) as compared to the leaves (16 %). It was concluded that the genotypes inoculated with CIAT899 and RhM₁₁ are relatively P-deficiency tolerant combinations as compared to those inoculated with RhM₁₄. Increase of oxidative stress in nodules rather than in leaves points to the need for further investigations of mechanisms that improve the root-nodule efficiency under adverse conditions.