ZnO NPs reveal distinction in toxicity under different spectral lights: An in vitro experiment on Brassica nigra (Linn.) Koch

Metallic nanoparticles (NPs) have been studied for their optimistic and pessimistic influence on plants growth and physiology under different light regimes. To investigate the influence of NPs under different light wavelengths, Brassica nigra (Linn.) Koch plants were grown on ZnO NPs supplemented media under the exposure of five different spectral lights (white, blue, red, yellow and green). ZnO NPs toxicity varied under different spectral lights. Difference in light wavelength significantly altered toxicity level of NPs on shoot root length and weight parameters of B. nigra. Free radical scavenging activity, total antioxidant response, and total reducing power potential also considerably varied in shoots and roots when plants were grown in presence of NPs and spectral lights. Concentration of total phenolics and flavonoids also changed in shoots and roots to combat NPs stress. HPLC analysis presented that chlorogenic acid upregulated under NPs influence in red and white light; while quercetin increased under NPs stress in blue light. The study shows that NPs have different toxicity response under different light wavelengths and plant behaves according to environmental conditions to mitigate NPs stress. However, detailed phytochemical and molecular studies are required to explain photodynamic toxicity of NPs.