Effects of cobalt oxide nanoparticles (Co3O4 NPs) on ion leakage, total phenol, antioxidant enzymes activities and cobalt accumulation in Brassica napus L.

Abstract

Interaction of nanoparticles (NPs) as a significant threat to ecosystems with biological processes of plants is very important. Here, the effects of cobalt oxide (Co3O4) NPs on some physio-biochemical characteristics of Brassica napus L. were investigated. The two-weeks seedlings were sprayed with different concentrations of Co3O4 NPs (0, 50, 100, 250, 500, 1000, 2000, and 4000 mg L-1). The results showed that this treatment significantly affected the fresh and dry weights, area, relative water content (RWC) and relative chlorophyll value (SPAD) of leaves. The highest reduction of growth and biomass indexes occurred at 4000 mg L-1 NPs. The content of H2O2 and electrolyte leakage (EL) increased respectively, after 100 and 250 mg L-1 of Co3O4 NPs and showed a maximum level at 4000 mg L-1. The activities of phenylalanine ammonia lyase (PAL), ascorbate peroxidase (APX) and superoxide dismutase (SOD) increased after 100 mg L-1 of Co3O4 NPs. However, tyrosine ammonia lyase (TAL) activity enhanced after 500 mg L-1. The catalase (CAT) activity and protein content decreased after 1000 mg L-1 of Co3O4 NPs. Application of concentrations higher than 500 mg L-1 of Co3O4 NPs induced polyphenol oxidase (PPO) activity but reduced glutathione reductase (GR). The activities of guaiacol peroxidase (GPX) and glutathione S-transferase (GST) increased at 250-1000 mg L-1 of Co3O4 NPs and then decreased. These results suggested that low concentrations of Co3O4 NPs induced a positive effect on growth parameters but high levels caused extensive oxidative damage and mediated defense responses by organization of phenolic compounds and antioxidative system.