Natural amelioration of Zinc oxide nanoparticle toxicity in fenugreek (Trigonella foenum-gracum) by arbuscular mycorrhizal (Glomus intraradices) secretion of glomalin.

Owing to rising production and use of engineered nanoparticles (ENPs) in the myriad of consumer applications, ENPs are being released into the environment where their potential fate and effects have remained unclear. With naturally occurring arbuscular mycorrhizal fungus (AMF; Glomus intraradices) in soils, their influence (positive or negative) on ENPs toxicity in plants is not well documented. Herein, we investigated potential influence of AMF on the growth and development in fenugreek (Trigonella foenum-graecum) under varied Zinc oxide nanoparticles (ZnONPs) treatments (0, 125, 250, 375 and 500 μg g-1). Results showed that in the absence of AMF, increasing ZnONPs concentrations caused significant decline in root nodule number and biomass in fenugreek. In non-AMF plants, shoot length, and biomass of both root and shoot decreased at ≥375 μg g-1 of ZnONPs treatment; while Zn uptake by shoot and root increased as a function of ZnONPs treatments. Interestingly, AMF colonization in roots significantly diminished at 375 μg g-1 ZnONPs treatment compared to controls. More importantly, AMF inoculation ameliorated inhibitory effects of ZnONPs by promoting secretion of glycoprotein called glomalin-a potent metal chelator-within the rhizosphere, which significantly reduced (by almost half) Zn uptake by root and subsequent translocation to the shoot. AMF inoculation (high glomalin secretion)-mediated low Zn uptake might have been stimulatory to promote root and shoot growth in fenugreek. The results highlight significant protective roles of rhizospheric AMF through glomalin secretion thereby ameliorating nanotoxicity in plants, and underscore the need to include soil-microbial interactions when assessing nanophytotoxicology and risks. Furthermore, potential positive implications to other organisms in the food chain can be inferred due to low tropic transfer of ENPs and/or associated toxic dissolved ions in the presence of naturally occurring soil fingi.