Changes in the lignan pattern of flax (Linum usitatissimum L.) in the course of plant development

Flax seed (L. usitatissimum L.) is one of the richest sources of precursors for enterolignans which possess chemopreventive potential against malignant tumours as well as cardiovascular and other diseases [1]. Secoisolariciresinol diglucoside (SDG) is the major lignan in the seeds where it occurs mainly in the form of oligomeric esters with hydroxymethylglutaric acid [1]. The major part of flax seed SDG possesses 8S, 8'S-configuration (SS-SDG) corresponding to (+)-secoisolariciresinol [1]. In the course of our ongoing studies on lignan diversity in the genus Linum, we have shown that adult L. usitatissimum plants contain a variety of lipophilic dibenzylbutryrolactone lignans, e.g. yatein, and that these compounds possess 8R, 8'R-configuration [2]. As a result of our present study, the latter compounds are not present in the seeds. In accordance with literature [1,3], SS-SDG along with p-coumaric- and ferulic acid glucosides (CAG, FAG) were detected as major constituents besides a minor amount of RR-SDG. Changes in lignan biosynthesis and accumulation must hence occur during development, i.e. from 8S, 8'S-configured lignans to such with R,R-configuration and from polar dibenzylbutane glucosides to lipophilic dibenzylbutyrolactones. We have hence begun to investigate changes in lignan pattern of L. usitatissimum during plant development. Seeds were germinated and samples harvested in one-day intervals over two weeks and analysed by HPLC using two different systems for polar [3] and non-polar constituents [2]. It was found that the formation of lipophilic lignans is neither initiated during germination nor related to the onset of photosynthesis or lignin formation. Neither the amounts of SS-SDG nor those of its stereoisomer are significantly increased in this phase. Developing plantlets contain only minor amounts of SDG, CAG and FAG, which appear to be restricted to the seed remnant. Instead, several polar phenolic components, some with lignan-like UV spectra, displayed a marked increase. Their identification is in progress while the study is continued over the whole lifetime of the plants.

Acknowledgement: We acknowledge financial support from Deutsche Forschungsgemeinschaft (DFG) grant # Schm 1166/2–2 and the valuable help by A. Frehe and C. Knickenberg, Münster, during an undergraduate research project.

References: [1] Westcott, N., Muir, A.D. (2003) Flax-The genus Linum. Taylor & Francis. London. [2] Schmidt, T.J. et al. (2006) Phytochem. Anal. 17: 299–311. [3] Eliasson, C. et al. (2003) J. Chromatogr. A. 1001: 151–159.