## Materials and Methods
### Analysis of Proline and Antioxidant Enzymes  
For the determination of proline contents in _Brassica juncea_ (L.) leaves, leaf sample (0.5 g) was processed by homogenization using sulphosalyclic acid (3%) in flasks as described by [PERSON] et al. [44]. After homogenization, the contents were filtered using Whatman No. 2 followed by adding acid ninhydrin and glacial acetic acid. The mixture was left in shaking water bath for one hour adjusting at 100 \({}^{\circ}\)C. After one hour, the flasks were \begin{table}
\begin{tabular}{c c c} \hline \hline
**Characteristic** & **Unit** & **Value** \\ \hline pH\({}_{\text{s}}\) & - & 7.9 \(\pm\) 1.3 \\ EC\({}_{\text{e}}\) & dS m\({}^{-1}\) & 1.61 \(\pm\) 0.23 \\ Available P & mg kg\({}^{-1}\) & 5.70 \(\pm\) 0.28 \\ Extractable K & mg kg\({}^{-1}\) & 89 \(\pm\) 3.54 \\ Organic matter & \% & 0.71 \(\pm\) 0.17 \\ Total nitrogen & \% & 0.05 \(\pm\) 0.014 \\ Total cadmium & mg kg\({}^{-1}\) & 1.12 \(\pm\) 0.34 \\ Total nickel & mg kg\({}^{-1}\) & ND \\ Total lead & mg kg\({}^{-1}\) & 0.4 \(\pm\) 0.11 \\ Total Fe & mg kg\({}^{-1}\) & 34 \(\pm\) 2.14 \\ Total Zn & mg kg\({}^{-1}\) & 39 \(\pm\) 3.28 \\ Textural class & - & Sandy clay loam \\ \hline \hline \end{tabular} ND = not detected; Number of replications = 03; EC\({}_{\text{e}}\) = Electrical conductivity of extract.  
\end{table} 
Table 1: Physico-chemical characteristics of soil used for pot experiment. cooled in ice bath to stop the reaction. The contents of the mixture were extracted using toluene followed by measuring the absorbance using spectrophotometer (Model; Carry 60; Agilent, Santa Clara, CA, USA) at 520 nm. The standard curve was prepared for the proline concentration measurements as described by [PERSON] et al. [44]. The proline value was expressed as umol g\({}^{-1}\). For the analysis of antioxidant enzymes, the samples were extracted according to the procedure as described by [PERSON] et al. [45] in which, the fresh plant tissues (0.5 g) were homogenized in a pestle mortal placed in an ice bath, by adding 5 mL of cooled 50 mM phosphate extraction buffer solution of pH 7.8 [Na\({}_{2}\)HPO\(\cdot\)12H\({}_{2}\)O (16.385 g) + NaH\({}_{2}\)PO\({}_{4}\cdot\)2H\({}_{2}\)O (0.663 g) dissolved in distilled water and making the final volume 1000 mL]. Afterwards, the homogenized mixture was centrifuged at 13,000\(\times\)_g_ for 10 min at 4 \({}^{\circ}\)C and the supernatant was used for the determination of antioxidants enzymes activities. The 50% inhibition in photochemical reduction of nitro blue tetrazolium (NBT) was recorded as one enzyme unit. The superoxide dismutase (SOD) activity was measured according to the method of [PERSON] [46]; the extracted sample (0.025 mL) was mixed with 0.25 mL of H\({}_{2}\)O\({}_{2}\) (300 mM) and 2.725 mL of reaction solution (75 uM NBT + 20 uM riboflavin + 100 uM EDTA-Na\({}_{2}\) + 130 mM methionine) along with control contain all the reagents except sample. The samples were incubated for 15 min in light to complete the reaction and the absorbances were measured at 560 nm wavelength on UV-VIS spectrophotometer (Model G6860A, Agilent Technologies Cary 60 UV-Vis, Mulgrave, Victoria, Australia). Afterwards the SOD activity was determined by the formula given in the Equation (1) provided by [PERSON] and [PERSON] [47]. For the determination of peroxidase (POX), 2.8 mL phosphate extraction buffer solution was mixed with 0.1 mL Guaiocl (1.5%), 0.1 mL H\({}_{2}\)O\({}_{2}\) (300 mM) and 0.1 mL of enzyme extract. The absorbance of the sample was taken at 470 nm on an ultraviolet-visible (UV-VIS) spectrophotometer. Whereas the catalase (CAT) activity was determined by the method of [PERSON] [48]. The final sample was made by mixing enzyme extract (0.1 mL) with 2.8 mL phosphate extraction buffer solution and 0.1 mL H\({}_{2}\)O\({}_{2}\) (300 mM). The absorbance of the final samples was measured on spectrophotometer at 240 nm wavelength. The POX and CAT activities were determined using Equation (2).