Assessment of silver nanoparticles contamination on faba bean-Rhizobium leguminosarum bv. viciae-Glomus aggregatum symbiosis: Implications for induction of autophagy process in root nodule

The current study sought to explore the response of application of purified silver nanoparticles (Ag NPs) to soil grown with faba bean ( Vicia faba L.) and inoculated either with Rhizobium leguminosarum bv. viciae ASU ( KF670819 ) or Glomus aggregatum 14G or in combination. Ag NPs was synthesized and stabilized using PVP and characterized by UV–vis spectroscopy and the characteristic surface plasmon resonance band centered at 430 nm. Also, the morphologies and structures of Ag NPs were characterized by X-ray diffraction and transmission electron microscopy and the size distribution ranged from 5 to 50 nm. In the first experiment, the germination and seedling growth of faba bean plants were tested under different concentrations of Ag + as AgNO 3 and Ag NPs (100–900 μg kg −1 soil). The germination declined by 40% when exposed to Ag NPs at concentration 800 μg kg −1 soil, while the same level from Ag + completely inhibited seed germination. In the second experiment the effect of a high concentration of Ag NPs (800 μg kg −1 soil) on R. leguminosarum bv. viciae growth and G. aggregatum activity in soil and their symbiosis with faba bean was investigated. It was proved that Ag NPs considerably retarded the process of nodulation, nitrogenase activity, mycorrhizal colonization, mycorrhizal responsiveness and glomalin content. High concentration of Ag NPs (800 μg kg −1 soil) resulted in detectable alterations including the intracellular deterioration of cytoplasmic components by means of autophagy and disintegration of bacteroids. These findings elucidate the mechanism of toxic action of Ag NPs which resulted in early senescence of root nodules.