Lead toxicity in Nicotiana tabacum L.: Damage antioxidant system and disturb plant metabolism

In this study, we treated tobacco seedlings with 0, 200, 400, and 800 mg/kg Pb^{2 +}, and explored the response mechanism of tobacco under Pb stress through a combination of growth physiology and metabolomics analysis. The physiological results showed that compared with CK, with the increase of Pb concentration, Pb treatment inhibited tobacco growth, reduced the biomass and photosynthetic pigment content of tobacco seedlings, and severely damaged the chloroplast structure. In addition, compared with CK, the pore conductivity and pore density of Pb800 treatment decreased by 45.77 % and 93.55 %, respectively. Pb treatment disrupted the cell membrane system, and Pb800 treatment increased the content of malondialdehyde (MDA) in leaves and roots by 67.65 % and 31.90 %, respectively. Meanwhile, Pb treatment increased the activity of tobacco SOD and POD enzymes. Metabolomics results showed that Pb stress enhanced tryptophan metabolism, glutathione metabolism, alanine, aspartate, and glutamate metabolism, as well as cysteine and methionine metabolism pathways. These results indicate that increasing the content of photosynthetic pigments and hormones, clearing reactive oxygen species by enhancing antioxidant enzyme activity, and improving amino acid metabolism may play an important role in reducing the toxicity of Pb to tobacco.