Glucosinolates in Wild-Growing Reseda spp. from Croatia

Abstract

Glucosinolates (GSLs) are a unique class of thioglucosides that evolved as defense mechanisms in the 16 families of the Brassicales order and present molecular tags which can be placed in a robust phylogenetic framework through investigations into their evolution and diversity. The GSL profiles of three Resedaceae species, Reseda alba, R. lutea, and R. phyteuma, were examined qualitatively and quantitatively with respect to their desulfo-counterparts utilizing UHPLC-DAD-MS/MS. In addition, NMR analysis of isolated 2-hydroxy-2-methylpropyl desulfoGSL (d31) was performed. Three Phe-derived GSLs were found in R. lutea, including glucotropaeolin (11) (0.6-106.69 mol g-1 DW), 2-(α-L-ramnopyranosyloxy)benzyl GSL (109) (8.10-57.89 μmol g-1 DW), glucolepigramin (22) (8.66 μmol g-1 DW in flower), and Trp-derived glucobrassicin (43) (0.76-5.92 μmol g-1 DW). The Phe-derived GSLs 109 (50.79-164.37 μmol g-1 DW), gluconasturtiin (105) (1.97 μmol g-1 DW), and 11 (tr), as well as the Trp-derived GSL glucobrassicin (43) (3.13-11.26 μmol g-1 DW), were all present in R. phyteuma. R. alba also contained Phe-derived 105 (0.10-107.77 μmol g-1 DW), followed by Trp-derived 43 (0.85-3.50 μmol g-1 DW) and neoglucobrassicin (47) (0.23-2.74 μmol g-1 DW). However, regarding the GSLs in R. alba, which originated from Leu biosynthesis, 31 was the major GSL (6.48 to 52.72 μmol g-1 DW) and isobutyl GSL (62) was the minor GSL (0.13 to 1.13 μmol g-1 DW). The discovered Reseda profiles, along with new evidence provided by GSL characterizations, were studied in the context of the current knowledge on GLSs in the Resedaceae family. With the exception of R. alba, the aliphatic GSLs of which were outliers among the Resedaceae species studied, this family typically contains GSLs derived primarily from Trp and Phe biosynthesis, which modifications resulted in GSLs unique to this family, implying presence of the specific genes. responsible for this diversification.