Silver nanoparticles affect wheat (Triticum aestivum L.) germination, seedling blight and yield.

The aim of the study was to evaluate the effect of two types of negatively charged quasi-spherical silver nanoparticles (AgNPs) at concentrations of 10, 20 and 30mgL-1 and silver ions at a concentration of 30mgL-1 on the growth, selected physiological aspects and yielding of wheat (Triticum aestivum L.) cv. Tybalt, and on plant resistance to seedling blight. Seed germination, α-amylase activity in seeds, morphology and infestation of seedlings by pathogens were assessed in a hydroponic treatment. Growth rate, PSII efficiency, heading and yield of the same plants were then analysed in pot culture. Results showed that the AgNPs and silver ions had a negative effect on roots, but reduced seedling blight and improved leaf area compared to the control. In addition, the AgNPs reduced with sodium borohydride in the presence of trisodium citrate at concentrations of 10 and 20mgL-1 stimulated germination, α-amylase activity and shoot length, which was not observed in the case of silver ions and the AgNPs reduced with sodium hypophosphite in the presence of sodium hexametaphosphate. In a pot experiment, the AgNPs improved plant growth, PSII efficiency, accelerated heading and increased yield-related parameters compared with the control. Results revealed the interaction strength in the following order: TCSB-AgNPs>SHSH-AgNPs>silver ions. TCSB-AgNPs in the lowest concentration had the most favourable effect, indicating their great potential for use in improving wheat cultivation.

Chemical Structure of Stabilizing Layers of Negatively Charged Silver Nanoparticles as an Effector of Shifts in Soil Bacterial Microbiome under Short-Term Exposure.

In this work, we have assessed the exposure of soil bacteria from potato monoculture to three types of silver nanoparticles (AgNPs) as well as silver ions (Ag+ ions) delivered in the form of silver nitrate and a commercially available fungicide. The diversity of the soil microbial community, enzymatic activity, and carbon source utilization were evaluated. It was found that only the fungicide significantly limited the abundance and activity of soil bacteria. Silver ions significantly reduced bacterial metabolic activity. In turn, one type of AgNPs prepared with the use of tannic acid (TA) increased bacterial load and activity. There was found in all AgNPs treated soils (1) a greater proportion of all types of persistent bacteria, i.e., Bacillus, Paenibacillus, and Clostridium; (2) a visible decrease in the proportion of Nocardioides, Arthrobacter, and Candidatus Solibacter; (3) almost complete depletion of Pseudomonas; (4) increase in the number of low-frequency taxa and decrease in dominant taxa compared to the control soil. Despite the general trend of qualitative changes in the bacterial community, it was found that the differences in the chemical structure of the AgNP stabilizing layers had a significant impact on the specific metabolic activity resulting from qualitative changes in the microbiome.

Surface properties-dependent antifungal activity of silver nanoparticles.

Silver nanoparticles (AgNPs) exhibit unusual biocidal properties thanks to which they find a wide range of applications in diverse fields of science and industry. Numerous research studies have been devoted to the bactericidal properties of AgNPs while less attention has been focused on their fungicidal activity. Our studies were therefore oriented toward determining the impact of AgNPs characterized by different physicochemical properties on Fusarium avenaceum and Fusarium equiseti. The main hypothesis assumed that the fungicidal properties of AgNPs characterized by comparable morphology can be shaped by stabilizing agent molecules adsorbed on nanoparticle surfaces. Two types of AgNPs were prepared by the reduction of silver ions with sodium borohydride (SB) in the presence of trisodium citrate (TC) or cysteamine hydrochloride (CH). Both types of AgNPs exhibited a quasi-spherical shape. Citrate-stabilized AgNPs (TCSB-AgNPs) of an average size of 15 ± 4 nm were negatively charged. Smaller (12 ± 4 nm), cysteamine-capped AgNPs (CHSB-AgNPs) were characterized by a positive surface charge and higher silver ion release profile. The phytopathogens were exposed to the AgNPs in three doses equal to 2.5, 5 and 10 mg L-1 over 24 and 240 h. Additionally, the impact of silver ions delivered in the form of silver nitrate and the stabilizing agents of AgNPs on the fungi was also investigated. The response of phytopathogens to these treatments was evaluated by determining mycelial growth, sporulation and changes in the cell morphology. The results of our studies showed that CHSB-AgNPs, especially at a concentration of 10 mg L-1, strongly limited the vegetative mycelium growth of both species for short and long treatment times. The cell imaging revealed that CHSB-AgNPs damaged the conidia membranes and penetrated into the cells, while TCSB-AgNPs were deposited on their surface. The fungistatic (lethal) effect was demonstrated only for silver ions at the highest concentration for the F. equiseti species in the 240 h treatment. The number of spores of both Fusarium species was significantly reduced independently of the type of silver compounds used. Generally, it was found that the positively charged CHSB-AgNPs were more fungicidal than negatively charged TCSB-AgNPs. Thereby, it was established that the stabilizing agents of AgNPs and surface charge play a crucial role in the shaping of their fungicidal properties.