Abstract：Rapeseed (Brassica napus) and Arabidopsis thaliana belonging to the same family Cruciferae have analogical mechanisms in regulating seed fatty acid (FA) accumulation. Rapeseed is a significant oil crop in China. Elevate its seed oil content is an important goal for rapeseed breeders since many decades. The seed oil content of Arabidopsis varies 20%~35%, and Arabidopsis can serve as an ideal model to study the mechanism of synthesis of FAs and other storage compound in seeds. Abscisic acid (ABA) is a plant endogenous hormone that regulates seed development, maturation and the acquisition of seed dormancy. However, little is known about the effect of ABA on accumulation of FAs and storage proteins in cruciferae oilseeds. In this study, ABA with different concentrations was applied to rapeseed as well as Arabidopsis plants which were at reproductive stage. In order to explore the effect of ABA on biosynthesis of FAs and other storage compounds such as protein in seeds, a series of culturing mediums containing various concentrations of ABA were used for the culture of fertilized rapeseed embryos 28 days after pollination (DAP). The results showed that ABA promoted the senescence of Arabidopsis leaves and rapeseed pods reflected by early yellowing. The spray of ABA (200 μmol/L) on Arabidopsis plants before bolting inhibited the development of siliques. Moreover, the spray of ABA repressed the expression of fatty acid elongation 1 (FAE1), inhibited the biosynthesis of very long chain fatty acids (VLCFA, C＞20), elevated the proportion of 18-carbon polyunsaturated fatty acid (PUFA), and decreased the proportion of storage protein, indirectly. On the other hand, the culturing of fertilized rapeseed embryos in vitro demonstrated that ABA repressed the expression of fatty acid desaturases (FADs), which further resulted in the reduction of PUFA the increases of VLCFAs and storage proteins. Taken together, the concentration of ABA is critical to seed FA accumulation, i.e., high (or low) ABA concentrations repressed (or promoted) the expression of genes on the FA biosynthesis pathway. Therefore, different concentrations of exogenous ABA could be applied to regulate seed FA accumulation positive or negatively. This research enriches knowledge about the function of ABA and the understanding about the molecular mechanism regulating the accumulation of fatty acids in oilseeds.
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