Abstract：Brassinolide has a promoting effect on crop growth. In order to clarify the effect of seed soaking on the seedlings of Brassica napus, the dry seeds were soaked in brassinolide, and the soaked in clear water were used as the control. The leaves at the 5~6 leaf stage were used for transcriptome sequencing analysis, and the leaves at young seedling stage, 5~6 leaf stage and budding stage were used for physiological and biochemical analysis. The results showed that transcriptome analysis found 4 066 up-regulated and 4 606 down-regulated differential genes. Three differential genes related to fatty acid synthesis were screened out: Fatty acyl carrier protein thioesterase (BnFAT), biological carboxyl carrier protein (BnBCCP), and stearoy acyl carrier protein desaturase (BnSAD); 3 differential genes related to photosynthesis were screened out: PhotoreactionⅠsystem centerⅤsubunit (BnPSAG), photosystemⅡreaction center protein PSB28 (BnPSB28) and chlorophyll ab-binding protein (BnCab).The qPCR method was used to verify the transcriptome results, and it was found that only BnSAD was inconsistent with the sequencing results, and the other 5 differential genes were consistent with the transcriptome sequencing results. Using the leaves at seedling stage, 5~6 leaf stage and budding stage as materials, the expression level of 6 differential genes was analyzed, and the soluble sugar, soluble protein content, superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) and other physiological functions were analyzed, and the correlation between the differential gene expression in 3 periods and the physiological and biochemical indicators were studied. The results showed that the expression of BnFAT and BnBCCP genes were positively correlated with the content of soluble sugar (both correlation coefficients were 0.69), BnCab expression was positively correlated with the content of soluble protein and SOD activity (correlation coefficients was 0.89 and 0.62, respectively), BnPSAG gene expression was positively correlated with POD activity (correlation coefficient was 0.62). The results of this study indicate that the treatment of seeds with brassinolide could increase the soluble substance content and protective enzyme activity of B. napus, and there was a close correlation between the physiological and biochemical indexes and the differential gene expression. This research could provide theoretical and technical reference for high-yield cultivation of rape.
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