*4.5. Non-Enzymatic Antioxidant Activities (TFC, TPC, and GSH)*

Our findings showed that the controlled and low temperature-treated leaves accumulated phenolic compounds differently during cold stress. Determining phenolic contents in response to stress can help research the cultivation tolerance mechanism and crop loss minimization. When exposed to stress, phenolic compounds serve as antioxidants and activate the cell's enzyme system [29]. In Figure 4a, it was noticed that most of the varieties showed a decreasing trend in low-temperature treatment, whereas the Y49 and M33 varieties showed significantly accelerated by 17.71% and 32.94%, respectively, and most reduced level was observed in T8 (12.08%) and Y1 (11.75%) compared to non-stressed conditions.

Like TPC, total flavonoid content (TFC) was enormously accelerated in Y49 (23.96%) and M33 (4.94%); whereas a high reduction rate was recorded in Y1, T38, T8, and W57 in stress conditions compared to control (Figure 4b). In the case of GSH, after 24 h low temperature stress, GSH contents were significantly increased in varieties Y49 (78.66%), M33 (45.65%), and M18 (4.86%) (Figure 4c). In contrast, the rest of the varieties demonstrated a decrease from 10.82~47.99%. The higher GSH level and homeostasis enhanced the antioxidant and glyoxalase systems' activity to alleviate cold-induced damage in the cold tolerant.

**Figure 4.** Influence of cold stress on enzymatic and non-enzymatic antioxidants in jute varieties. Plants under control (28 ◦C) and stress (5 ◦C) showed a response in: (**a**) Total polyphenol, (**b**) Total flavonoid, and (**c**) GSH activity. Different significant level marked with \*\*\*\* *p* < 0.0001, \*\*\* *p* ≤ 0.001, \*\* *p* ≤ 0.01, \* *p* ≤ 0.05, and ns mean non-significant.
