| Brassica oilseeds (in particular Brassica napus) are one of the most important sources of edible oils of the world. The nutritional value of Brassica oils are mainly determined by the proportion of desired constituent fatty acids (FAs), i.e. rapeseed oils with high C18:1and C18:2compositions are most welcome due to their health and cooking benefits. Besides FAs, the content and composition of vitamin E (tocochromanols) is other important parameters to be considered in the breeding programs of Brassica oilseeds.Vitamin E is a powerful fat-soluble antioxidant synthesized only by photosynthetic organisms, indispensable for the protection of PUFA (polyunsaturated fatty acids) against oxidative deterioration in both plants and animals. It has beneficial effects in the prevention of cardiovascular diseases. In animals, vitamin E deficiency has severe consequences, including neurological dysfunction, muscular dystrophy and so on. The term’tocochromanol’ refers to two kinds of compounds:tocopherols (Ts) and tocotrienols. Both compounds exhibit vitamin E activity. However, Ts tend to be more common in seed oils (e.g. in rapeseed oils) than tocotrienols. Ts exist in four forms, α-,β-,γ-and8-T, differing from each other in both molecular structure and biological effectiveness. Among these four isoforms, a-T has the highest vitamin E efficacy, whereas y-T is the superior antioxidant in plant oils.Increasing the C18:1and C18:2FAs as well as total T and a-/y-tocopherol (a-/y-T) ratio is an important goal for breeding programs of Brassica oilseeds. However, there is a paucity of studies on the correlations among the T and FA components in Brassica oilseeds and on the identification of allelic variations of candidate genes encoding enzymes on the T biosynthetic pathway and the association with T content and composition in rapeseed (B. napus). Our following studies contribute to address the above mentioned questions.A germplasm collection of landraces (162accessions) from the species B.juncea, B. rapa, and B.napus and a collection of low erucic acid (EA) breeding lines (15 accessions) from B. napus were analyzed for FA and T contents. In the groups comprising landraces, the most notable correlation was the significantly positive one between a-T and the sum of C18:1and C18:2, whereas neither positive correlations were found between a-T and C18:3nor were positive correlations observed between a-T and very long chain FAs (VLCFA). Hardly any association between y-T and FA components was observed, indicating the possible function of a-T beyond its antioxidant property. The complexity of correlation between T and FA components in Brassica oils may arise from the role of a-T in the FA metabolism of endoplasmic reticulum (ER).A set of25intron-spanning primers were used to identify the allelic variations of candidate genes (BnaX.PDS1.b, BnaX.VTE1.a, BnaA.VTE2.a, BnaX.VTE3.a, BnaX.VTE4.b, BnaC.VTE5) encoding enzymes on the T biosynthetic pathway in a total of83accessions of rapeseed genotypes (B. napus). Among primer pairs designed on a certain gene locus, at least one of the pairs can be used for a successful detection of about3or4bands by PCR amplification and the consequent capillary electrophoretic separation. The multiple bands indicated the number of homologous copies of candidate genes in rapeseed genome for the gene investigated. Using the ’Q+K’model for statistic analysis,6out of49loci that exhibited dominant/recessive polymorphisms were found to be be significantly associated with T content and/or composition. Notably, a molecular marker of369bp in length, which could be amplified using the primer pair of PDS1-IP1(F/R) and demonstrated on capillary electrophoresis gel, contributed to8.12%and5.48%variations of total T and a-T contents, repectively. The marker is, therefore, recommended for molecular assisted rapeseed breeding projects for ideal tocopherol quality. |
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