In vitro toxicity of silver nanoparticles to kiwifruit pollen exhibits peculiar traits beyond the cause of silver ion release

The vast use of silver nanoparticles (AgNPs) mandates thorough investigation of their impact on biosystems at various levels. The cytotoxicity of PVP coated-AgNPs to pollen, the aploid male gametophyte of higher plants, has been assessed here for the first time. The negative effects of AgNPs include substantial decreases in pollen viability and performance, specific ultrastructural alterations, early changes in calcium content, and unbalance of redox status. Ag+ released from AgNPs damaged pollen membranes and inhibited germination to a greater extent than the AgNPs themselves. By contrast, the AgNPs were more potent at disrupting the tube elongation process. ROS deficiency and overproduction were registered in the Ag+- and AgNP-treatment, respectively. The peculiar features of AgNP toxicity reflected their specific modes of interaction with pollen surface and membranes, and the dynamic exchange between coating (PVP) and culture medium. In contrast, the effects of Ag+ were most likely induced through chemical/physicochemical interactions. -- Highlights: •Kiwifruit pollen was treated with 10 nm-sized PVP-coated AgNPs. •Pollen lethality increased with increasing either nanosized or ionic silver dose. •At the ultrastructural level, AgNP-specific alteration of plasmalemma appeared. •Pollen tube emergence and elongation were differently sensitive to AgNPs and Ag+. •In the pollen model, the biological potency of AgNPs did not match that of Ag+. -- AgNP toxicity to pollen does not match the effects of released Ag+