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

Abstract

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 430nm. 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 50nm. In the first experiment, the germination and seedling growth of faba bean plants were tested under different concentrations of Ag+ as AgNO3 and Ag NPs (100–900μgkg−1 soil). The germination declined by 40% when exposed to Ag NPs at concentration 800μgkg−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 (800μgkg−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 (800μgkg−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.