Glanduläre Trichome und Isoprenoidbiosynthese

In Brassica napus, suppression of the key biosynthetic enzyme UDP-glucose:sinapic acid glucosyltransferase (UGT84A9) inhibits the biosynthesis of sinapine (sinapoylcholine), the major phenolic component of seeds. Based on the accumulation kinetics of a total of 158 compounds (110 secondary and 48 primary metabolites), we investigated how suppression of the major sink pathway of sinapic acid impacts the metabolome of developing seeds and seedlings. In UGT84A9-suppressing (UGT84A9i) lines massive alterations became evident in late stages of seed development affecting the accumulation levels of 58 secondary and 7 primary metabolites. UGT84A9i seeds were characterized by decreased amounts of various hydroxycinnamic acid (HCA) esters, and increased formation of sinapic and syringic acid glycosides. This indicates glycosylation and β-oxidation as metabolic detoxification strategies to bypass intracellular accumulation of sinapic acid. In addition, a net loss of sinapic acid upon UGT84A9 suppression may point to a feedback regulation of HCA biosynthesis. Surprisingly, suppression of UGT84A9 under control of the seed-specific NAPINC promoter was maintained in cotyledons during the first two weeks of seedling development and associated with a reduced and delayed transformation of sinapine into sinapoylmalate. The lack of sinapoylmalate did not interfere with plant fitness under UV-B stress. Increased UV-B radiation triggered the accumulation of quercetin conjugates whereas the sinapoylmalate level was not affected.

The seed residues left after pressing of rapeseed oil are rich in proteins and could be used for human nutrition and animal feeding. These press cakes contain, however, antinutritives, with fiber being the most abundant one. The analysis of fiber phenolic component (localized to seed coat cell walls) is, therefore, important in breeding and food quality control. However, correct structure and content assignments of cell wall-bound phenolics are challenging due to their low stability during sample preparation. Here, a novel LC-MS/MS-based method for the simultaneous identification and quantitation of 66 cell wall-bound phenolics and their derivatives is described. The method was internally standardized, corrected for degradation effects during sample preparation, and cross-validated with a well-established UV-based procedure. This approach was successfully applied to the analysis of cell wall phenolic patterns in different B. napus cultivars and proved to be suitable for marker compound search as well as assay development.