Physiological and molecular responses to cold stress in rapeseed (Brassica napus L.)

Low temperature is one of the most important abiotic factors inhibiting growth, productivity, and distribution of rapeseed (Brassica napus L.). Therefore, it is important to identify and cultivate cold-tolerant germplasm. The objective of this study was to figure out the mechanism of chilling (4 and 2 degrees C) and freezing (-2 and -4 degrees C) stresses along with a control (22 degrees C) in B. napus cultivars (1801 and C20) under controlled environment (growth chamber). The experiment was arranged in a complete randomized design with three replications. Our results exhibited that under chilling and freezing stresses, the increment of proline accumulation, soluble sugar and protein contents, and antioxidant enzyme activity were enhanced more in 1801 cultivar compared with C20 cultivar. At -2 and -4 degrees C, the seedlings of C20 cultivar died completely compared with 1801 cultivar. Hydrogen peroxide (H2O2) and malondialdehyde contents (MDA) increased in both cultivars, but when the temperature was decreased up to -2 and -4 degrees C, the MDA and H2O2 contents continuously dropped in 1801 cultivar. Moreover, we found that leaf abscisic acid (ABA) was enhanced in 1801 cultivar under chilling and freezing stresses. Additionally, the transcriptional regulations of cold-tolerant genes (COLD1, CBF4, COR6.6, COR15, and COR25) were also determined using real-time quantitative PCR (RT-qPCR). RT-qPCR showed that higher expression of these genes were found in 1801 as compared to C20 under cold stress (chilling and freezing stresses). Therefore, it is concluded from this experiment that 1801 cultivar has a higher ability to respond to cold stress (chilling and freezing stresses) by maintaining hormonal, antioxidative, and osmotic activity along with gene transcription process than C20. The result of this study will provide a solid foundation for understanding physiological and molecular mechanisms of cold stress signaling in rapeseed (B. napus).