*4.1. Effect of Cold Stress on Photosynthetic Pigment Contents*

Low temperature impacts chlorophyll level in plant species based on their cold tolerance [27,28]. To determine the effect of cold stress on photosynthesis, we measured chlorophyll *a* and *b* concentrations and total chlorophyll in jute plant leaves. The results of our experiment indicated that the production of photosynthetic pigments (Chl *a*, Chl *b,* and Total Chl) varied significantly between selected varieties, with variation patterns being comparable across all varieties (Table 2). It was observed that the total chlorophyll concentration of leaves declined with cold stress compared to their control. Greater decrease was observed in the varieties Y38 and T8, whereas a lower reduction rate was observed in Y49 and M33 varieties with the highest chlorophyll stability index (CSI) as 97.96% and 90.97%, respectively. Our findings suggested that these varieties were less harmed at 5 ◦C and more resistant to chilling injury than others, implying that they possessed a greater cold tolerance. In the case of the carotenoid content, a similar trend was observed as chlorophyll; except for Y49, all varieties showed declined trend compared to control. Meanwhile, the Y38 and T8 recorded significantly decreased by 18.46% and 19.62%, respectively, relative to control, and an increase and slight decrease was observed in Y49 and M33, respectively. This result suggests that Y49 and M33 have more low-temperature tolerance potential, whereas Y38 and T8 demonstrate a low degree of tolerance.
