Sequential Changes in Antioxidant Potential of Oakleaf Lettuce Seedlings Caused by Nano-TiO2 Treatment

Nowadays, there is an increasing interest in nanoparticle (NP) technology used in household and industrial products. It could cause an accumulation and dispersion of NPs in the environment, with possible harmful effects on living organisms. Nanoparticles significantly affect plants and alter their physiology and biochemical pathways, and nanotechnology can be used to improve plant characteristics that are desirable by humans. Therefore, more extensive studies of NP interactions with plants are still needed. The aim of this report is to investigate the effect of TiO2 nanoparticles (TiO2-NPs) on the enzymatic and non-enzymatic antioxidants, fresh and dry weights, and malondialdehyde contents in oakleaf lettuce seedlings. Plants were foliar treated with a 0.75% suspension of TiO2-NPs, while control plants were sprayed with deionized water. Leaves were sampled 4, 7, 9, 11, and 13 days after the treatment. The effects of TiO2-NPs were time-dependent, but the most spectacular changes were observed 4 days after the treatment. Exposure of the plants to TiO2-NPs significantly increased the contents of glutathione at all sampling points, total phenolics at days 4 and 13, and L-ascorbic acid at 4, 7, and 11 days after the treatment. Elevated levels of ascorbate peroxidase and guaiacol peroxidase activities were recorded at days 4 and 13, respectively. Total antioxidant capacity increased initially in treated seedlings, when compared with the control, and then decreased. On day 7, higher fresh and dry weights, as well as malondialdehyde contents in TiO2-NPs treated plants were observed, compared with the control. The study demonstrated that the activation of some antioxidant system components due to TiO2-NPs treatment was connected with the induction of mild oxidative stress, with no external symptoms of NP toxicity in oakleaf lettuce.