Oilseed rape (Brassica napus subsp. oleifera L.) and turnip rape (Brassica rapa var. oleifera L.) are important oil crops widely grown in Europe. Oilseed rape gives higher yields, but requires a longer growing season than turnip rape, making turnip rape more important in the northern latitudes. The seed oil consists largely of triacylglycerols (TAGs) that are synthesized through the Kennedy pathway during seed development. The oil is considered nutritionally important due to its well-balanced fatty acid content, and a favorable n–6 / n–3 fatty acid ratio.

The aim of this work was to study the biosynthesis of TAGs in developing seeds of each species. We targeted the problem by studying the expression of genes encoding enzymes in the TAG synthesis pathway in a time series collected from three replicate experiments using one commonly cultivated cultivar of each species (oilseed rape ‘Marie’ and turnip rape ‘SW Petita’). The study was conducted using quantitative PCR for the genes of interest. Our results show the expression levels of different enzyme genes at 2, 3, 4, 5, and 6 weeks after flowering at different controlled growth conditions. The expression of the genes encoding sn-glycerol-3-phosphate acyltransferase 9 (GPAT9), lysophosphatidic acid phosphatase 4 (LPAAT4) and diacylglycerol acyltransferase 2 (DGAT2) appears to be under similar regulation in oilseed rape, suggesting roles for these enzymes as the main enzymes of the Kennedy pathway in the studied plants. Turnip rape cultivars are generally speaking more heterogeneous and the putative co-regulation could not be detected in them. When the plants were exposed to stress (cold temperature, 15°C; or short 12-hour day length), their seed development slowed down and the gene expression peaked later. These results were complemented with analysis of fatty acid and TAG composition at the same time points using gas chromatography (GC) and high performance liquid chromatography (HPLC).

The oil of the turnip rape cultivar contained a higher proportion of polyunsaturated fatty acids (PUFAs, 18:2(n–6) and 18:3(n–3)) in the TAG fraction than the oilseed rape cultivar. The proportion of PUFAs was increased by cold temperature treatment especially in turnip rape. The proportion of monounsaturated 18:1(n–9) fatty acid increased during seed development in all conditions.