Investigating growth responses and expression patterns of nicotine biosynthesis genes in tobacco plants treated with cadmium

Abstract

Cadmium (Cd), an unnecessary trace element in plants, destructively affects ecosystems. This pollutant exists everywhere in the environment, enters the plant through the soil, and causes extensive changes from the macro to the cellular level. This study investigated the effect of cadmium chloride (CdCl₂) at three concentrations of 0, 1, and 1.5 mM on morphological, biochemical, and molecular indicators in the Nicotiana tabacum plant as a significant agricultural plant and a common model organism. The results showed that an increase in CdCl₂ concentration significantly decreased plant growth and the concentration of photosynthetic pigments compared to the control plant. In contrast, the amounts of soluble sugar, free amino acids, and total phenol increased in plants under stress. In addition, the amount of nicotine and the expression of genes related to the pathway of nicotine biosynthesis increased in plants under Cd stress. The expression of NtA622, NtQPT, NtODC, and NtPMT genes at 1 mM CdCl₂ increased by 2, 1.7, 2.4, and 2.9 times, respectively, and at 1.5 mM, CdCl₂ increased by 2.9, 2.2, 2.7, and 3.8 times, respectively, compared to the control plant. Therefore, among the four studied genes, the relative expression of the NtPMT gene (the significant gene of the nicotine biosynthesis pathway) was higher. The nicotine content increased by 17.9% and 25.4% with 1- and 1.5-mM CdCl₂ compared to the control plant. Tobacco cultivation in Cd-contaminated environments should be managed and it seems that using Cd can increase the biosynthesis of nicotine for agricultural and medicinal purposes.