Physiological and molecular responses of basil (Ocimum basilicum) to silver stress: a comparison between silver nanoparticles and silver nitrate treatments

Abstract

With the extensive utilization of nanotechnology, silver nanoparticles (AgNPs) are prevalent nanomaterials that may entail ecological risks by their potential translocation into plant systems. The present study investigated the physiological and molecular responses of basil seedlings (Ocimum basilicum) subjected to AgNPs or silver nitrate (AgNO₃) for 7 days. The seedlings were treated with 0, 4, 10, or 40 mg/L of AgNO₃ or AgNPs in Hoagland’s solution. Both treatments resulted in significant accumulation of Ag in the roots and shoots, with higher levels in the roots of AgNO₃-treated seedlings. AgNPs increased plant biomass at 4 mg/L, while AgNO₃ decreased it at all concentrations. Both treatments reduced the total chlorophyll, carotenoids, and carbohydrates, with more pronounced effects in AgNO₃-treated seedlings. Both treatments also induced oxidative stress, as indicated by increased levels of H₂O₂, malondialdehyde (MDA), and proline, and enhanced activity of antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX). However, these responses were more evident in AgNO₃-treated seedlings, especially at higher concentrations. Quantitative real-time PCR analysis revealed that both treatments induced the upregulation of genes encoding oxidative stress tolerance-related enzymes, such as FSD1, MSD1, CSD1, CATa, CATb, APXa and APXb, in the basil seedling shoots. These results suggest that AgNPs are less toxic to basil plants than AgNO₃ and that basil plants can activate physiological and molecular mechanisms to cope with Ag-induced oxidative stress.