*4.2. Oxidative Stress Evaluation*

Lipid peroxidation, reflected by MDA content, usually accompanies ROS accumulation. Our experiment examined the effects of MDA content, and it showed that concentrations were considerably greater than the control. The highest increase was observed in Y38 (91.26%) and Y1 (65.81%), followed by T8 (48.82%). Whereas low level of MDA content was observed in Y49 (17.25%) and M33 (11.50%) varieties compared to optimal temperature (Figure 1a). The above result indicated that Y49 and M33 varieties suffered the least and cell membrane experienced little damage under cold injury, whereas Y1, Y38, and T8 varieties might have suffered severe and irreversible damage. The result of this study demonstrated that H2O2 content significantly increased under cold treatment conditions compared to control based on mean comparisons (Figure 1b). However, the lowest increase was noted in the varieties Y49 (11.64%) and M33 (17.25%). Whereas the Y38, T8, and M18 varieties showed a greater increase of H2O2 by 30.70~46.61% under low-temperature treatment than in the optimum temperature.



Significant difference at *p* < 0.05 probability level using LSD test. Values in the table represent means and standard errors. Different lowercases indicate difference significant at 0.05 level.

#### *4.3. Effect of Cold Stress on Osmolytes Contents*

The present investigation has shown that proline content is higher in leaves of stress treatment than under room temperature when exposed to 5 ◦C (Figure 2a). The most elevated proline was recorded in Y49, followed by M33 with 67.84% and 60.0% increased rate on cold stress compared to control condition, whereas the lowest increase was recorded in T8 (7.89%) and Y38 (11.39%)

In comparison to the control group after 24 h at 5 ◦C, our results revealed that total soluble sugar content of the leaves in most of the varieties demonstrated decline except Y49 and M33 (significantly increased by 16.77~24.99% and reached in highest in lowtemperature treatment compared to other) (Figure 2b). Conversely, the highest rate of decrease was observed in the varieties T8 (30.07%) and Y38 (27.81%) compared to other varieties in stress treatment.

**Figure 2.** Response of jute varieties to low temperature treatments, with control (28 ◦C) and stress (5 ◦C) showing differential response in osmolyte content. (**a**) Proline content, (**b**) Soluble sugar content. Different significant level marked with \*\*\*\* *p* < 0.0001, \*\*\* *p* ≤ 0.001, \* *p* ≤ 0.05, and ns mean non-significant.
