Foliar Exposure of Fe3O4 Nanoparticles on Nicotiana benthamiana: Evidence for Nanoparticles Uptake, Plant Growth Promoter and Defense Response Elicitor against Plant Virus

Abstract Nanoparticles are recently employed as a new strategy to directly kill pathogens (e.g., bacteria and fungus) and acted as nanofertilizers. However, the influences of this foliar deposition of nanoparticles on plant physiology particularly plant immunity are poorly understood. The uptake and physiological effects of Fe3O4 nanoparticles (Fe3O4NPs), and plant resistance response against Tobacco mosaic virus (TMV) after foliar spraying were studied. Specifically, Fe3O4NPs entered leaf cells and were transported and accumulated throughout the whole Nicotiana benthamiana plant, and increased plant dry and fresh weights, activated plant antioxidants, and upregulated SA synthesis and the expression of SA-responsive PR genes (i.e., PR1 and PR2), thereby enhancing plant resistance against TMV. Conversely, the viral infection was not inhibited in the NahG transgenic plants treated by Fe3O4NPs, suggesting the involvement of salicylic acid (SA) induced by Fe3O4NPs in the production of plant resistance. Moreover, no inhibition was observed of the infection after inoculating with the pretreated TMV mixtures. Thus, the deposition of Fe3O4NPs induced the accumulation of endogenous SA, which was correlated with the plant resistance against TMV infection. Such information is vital for valuing the risk of Fe3O4NPs products and broadens the researching and applying nanoparticles in the fight against plant diseases meantime.