No abstract

In the present study, a range of benzoxazinoid compounds and phenolic acids, all known to be allelochemicals of rye, were identified and quantified in 13 rye cultivars grown at three different localities. Plant samples were collected in the spring at the time when an autumn-sown rye cover crop would be incorporated into the soil. Significant variations in content among shoots and roots were seen for all of the secondary metabolites, with non-methoxy-substituted benzoxazinoids (BX) dominating the shoots, whereas comparable levels were found in the concentrations of BX and methoxy-substituted benzoxazinoids (MBX) in the roots. This distribution of compounds may indicate different biosynthetic pathways and/or different mechanisms of action of these compounds. Concentrations not only depended on plant part, but also on the geographical location-with differences in contents of up to a factor of 5. These differences can probably be attributed to differences in growing conditions. The variation among cultivars was similar to that among geographical localities, with differences within localities of up to a factor of 7 in the shoots and a factor of 14 in the roots. In roots, the contents of the four phenolic acids and the benzoxazinoid 6-methoxybenzoxazolin-2-one (MBOA) were correlated. In shoots, the contents of the two benzoic acids were correlated with each other, whereas the two cinnamic acids were correlated with MBOA and several other benzoxazinoids. The lack of correlation between MBOA and all other benzoxazinoids in the roots of rye might indicate that a hitherto unknown synthetic pathway exists for MBOA. The genes responsible for the synthesis of some of the benzoxazinoids have never been identified, and further gene expression studies are required to assess the observed correlation between the concentration of these compounds and other benzoxazinoids for which the responsible genes are known. The present study revealed a potential for breeding rye cultivars with a high content of biologically active secondary metabolites. However, growing conditions significantly influenced the level of these compounds.

In the present study, the major flavonoids of white clover (Trifolium repens L.) cv. Sonja were extracted, isolated and identified. The major flavonoids in leaves and stems were the four flavonol glycosides: kaempferol-3-O-{Xyl(1→2)-Gal} (kaempferol-Xyl-Gal), kaempferol-3-O-{Rha(1→6)-[Xyl(1→2)]-Gal} (kaempferol-Rha-Xyl-Gal), quercetin-3-O-{Xyl(1→2)-Gal} (quercetin-Xyl-Gal), and quercetin-3-O-{Rha(1→6)-[Xyl(1→2)]-Gal} (quercetin-Rha-Xyl-Gal). Quercetin-Rha-Xyl-Gal has never been reported before and kaempferol-Rha-Xyl-Gal has not previously been identified in clover aerial parts. Concentrations of those compounds, together with aglyconic flavonoids previously described in white clover, as well as their glycosides, were quantified in leaves/stems and flowers of four white clover cvs Rabani, Klondike, Ramona and Aran using tandem mass spectrometry. There were significant differences in flavonoid concentrations in the two plant parts, with the highest concentrations of most aglycones in flowers and the highest concentrations of most glycosides in leaves/stems. This distribution of compounds may indicate different ways of storage and/or different mechanisms of action of the compounds. The cultivars were selected for genetic diversity, which resulted in distinctly different amounts of flavonoids in the plants. Concentrations of 17 of 24 compounds varied significantly-for some compounds up to a factor of 10-among cultivars. Total flavonoid concentrations in flowers did not vary greatly among cultivars, at 28.9-35.8 mmol/g dry material (DM). In contrast, in leaves/stems, the cvs Rabani and Klondike had lower concentrations of most flavonoids (total concentrations 10.0 and 12.7 mmol/g DM , respectively) compared to cvs Aran and Ramona (32.3 and 22.1 mmol/g DM , respectively). There is a potential for breeding/selection of cultivars with targeted concentrations of particular flavonoids.

Hydroxamic acids are important defense compounds in cereals and have been subject to extensive research. Two important hydroxamic acids in maize are 2-β-D-glucopyranosyloxy-4-hydroxy-7-methoxy-2 H-1,4-benzoxazin-3(4 H)-one (DIMBOA-glc) and its 8-methoxylated derivative (DIM2BOA-glc). The compounds are typically reported as resolved by mass spectrometry rather than chromatography, with DIM2BOA-glc quantified relative to DIMBOA-glc. Biphenyl HPLC columns, however, allow good separation of the two compounds at both the analytical and semi-preparative scale, enabling both isolation and absolute quantitation of both compounds. In combination with established sample treatment and chromatographic methods, biphenyl chromatography thus promises new possibilities for resolving benzoxazinoid glucosides.

Barley (Hordeum vulgare) is an important cereal that has many applications; as a human food, in malt products and as livestock feed. The content of soluble health-promoting fibers, β-glucans, varies substantially among barley varieties. In the present study, the content of secondary metabolites with potential positive health effects in different high- and low-β-glucan barley varieties was studied. Five different flavanols were isolated and identified: (2 R,3 S)-catechin-7- O-β-D-glucopyranoside (1), prodelphinidin B3 (2), procyanidin B3 (3), (+)-catechin (4) and procyanidin B1 (5). Procyanidin B1 has never been reported in barley grains before. The compounds were identified using 1H NMR and quadrupolar time-of-flight mass spectrometry. A quantitative analytical method was developed for prodelphinidin B3, procyanidin B3 and (+)-catechin in liquid chromatography triple quadrupole-linear ion trap mass spectrometry and these compounds were quantified in all varieties, together with four phenolic acids: ferulic acid, vanillic acid, p-coumaric acid and p-hydroxybenzoic acid. Catechin was the compound that was present at the highest concentration in all varieties. The variation, between cultivars, in catechin concentration varied four fold. A Principal Component Analysis indicated no correlation between concentrations of β-glucan and secondary metabolites. Concentrations of catechin and prodelphinidin B3 were strongly correlated, whereas the concentration of procyanidin B3 was not correlated with that of catechin or prodelphinidin B3. Either two different enzymes could be responsible for the dimerization of prodelphinidin B3 and procyanidin B3, or the affinity of the enzyme could be different whether the dimerization is between two catechin units or between units of gallocatechin and catechin.