AMELIORATION with silicon (1mM sodium silicate Na₂SiO₃) or humic acid (50mg L^-1 HA) was tested in counteracting the phytotoxicity of copper oxide nanoparticles (CuONPs) at 50, 100 and 150mg L^-1 on Safflower plants (Carthamus tinctorius). Si sustained seed growth at (150mg L^-1 CuO NPs). The application of HA increased copper concentration in seedling by about 5 to 10 fold, relative to the control at 50 and 100mg L^-1. Fresh weight of safflower seedlings were reduced significantly at 100mg L^-1 CuO NPs. Si enhanced fresh and dry matter gain under 100 and 150mg L^-1 CuO NPs, also HA improved dry matter at 100mg L^-1 CuO NPs. Chlorophyll a and carotenoid contents reduced by about 60% and 50% at CuO NPs (100mg L^-1), respectively as compared to control. Chlorophyll a and carotenoid contents reduced by about 60% and 50% at CuO NPs (100mg L^-1), respectively as compared to control. Si or HA sustained Chl.a content unchanged and improved carotenoids contents at 100mg L^-1 CuO NPs.
Phenolics contents significantly increased under CuO NPs phytotoxicity. External application of HA provoked more phenolics content. Nano-CuO phytotoxicity reduced H₂O₂ scavenging and lipid peroxidation inhibition %. Si or HA enhanced significantly lipid peroxidation inhibition % and H₂O₂ radial scavenging %. Si or HA reflected significant enhancement of SOD and CAT enzymes under elevating concentrations of CuO NPs. Si enhanced significantly POD activity at (50, 100 and 150mg L^-1) CuO NPs levels.