| Title: | The pectic disaccharides lepidimoic acid and beta-d-xylopyranosyl-(1-->3)-d-galacturonic acid occur in cress-seed exudate but lack allelochemical activity |
| Author(s): | Iqbal A; Miller JG; Murray L; Sadler IH; Fry SC; |
| Address: | "The Edinburgh Cell Wall Group, Institute of Molecular Plant Sciences, The University of Edinburgh, The King's Buildings, Edinburgh EH9 3BF, UK and. EastChem School of Chemistry, The University of Edinburgh, The King's Buildings, Edinburgh EH9 3JJ, UK. The Edinburgh Cell Wall Group, Institute of Molecular Plant Sciences, The University of Edinburgh, The King's Buildings, Edinburgh EH9 3BF, UK and s.fry@ed.ac.uk" |
| ISSN/ISBN: | 1095-8290 (Electronic) 0305-7364 (Print) 0305-7364 (Linking) |
| Abstract: | "BACKGROUND AND AIMS: Cress-seed (Lepidium sativum) exudate exerts an allelochemical effect, promoting excessive hypocotyl elongation and inhibiting root growth in neighbouring Amaranthus caudatus seedlings. We investigated acidic disaccharides present in cress-seed exudate, testing the proposal that the allelochemical is an oligosaccharin-lepidimoic acid (LMA; 4-deoxy-beta-l-threo-hex-4-enopyranuronosyl-(1-->2)-l-rhamnose). METHODS: Cress-seed exudate was variously treated [heating, ethanolic precipitation, solvent partitioning, high-voltage paper electrophoresis and gel-permeation chromatography (GPC)], and the products were bioassayed for effects on dark-grown Amaranthus seedlings. Two acidic disaccharides, including LMA, were isolated and characterized by electrophoresis, thin-layer chromatography (TLC) and nuclear magnetic resonance (NMR) spectroscopy, and then bioassayed. KEY RESULTS: Cress-seed exudate contained low-Mr, hydrophilic, heat-stable material that strongly promoted Amaranthus hypocotyl elongation and inhibited root growth, but that separated from LMA on electrophoresis and GPC. Cress-seed exudate contained approximately 250 micromLMA, whose TLC and electrophoretic mobilities, susceptibility to mild acid hydrolysis and NMR spectra are reported. A second acidic disaccharide, present at approximately 120 microm, was similarly characterized, and shown to be beta-d-xylopyranosyl-(1-->3)-d-galacturonic acid (Xyl-->GalA), a repeat unit of xylogalacturonan. Purified LMA and Xyl-->GalA when applied at 360 and 740 microm, respectively, only slightly promoted Amaranthus hypocotyl growth, but equally promoted root growth and thus had no effect on the hypocotyl:root ratio, unlike total cress-seed exudate. CONCLUSIONS: LMA is present in cress seeds, probably formed by rhamnogalacturonan lyase action on rhamnogalacturonan-I during seed development. Our results contradict the hypothesis that LMA is a cress allelochemical that appreciably perturbs the growth of potentially competing seedlings. Since LMA and Xyl-->GalA slightly promoted both hypocotyl and root elongation, their effect could be nutritional. We conclude that rhamnogalacturonan-I and xylogalacturonan (pectin domains) are not sources of oligosaccharins with allelochemical activity, and the biological roles (if any) of the disaccharides derived from them are unknown. The main allelochemical principle in cress-seed exudate remains to be identified" |
| Keywords: | "Biological Assay Brassicaceae/*metabolism Chromatography, Gel Chromatography, Thin Layer Disaccharides/*metabolism Electrophoresis Glycosides/*metabolism Hexuronic Acids/*metabolism Hot Temperature Hydrophobic and Hydrophilic Interactions Hypocotyl Magnet;" |
| Notes: | "MedlineIqbal, Amjad Miller, Janice G Murray, Lorna Sadler, Ian H Fry, Stephen C eng Research Support, Non-U.S. Gov't England 2016/03/10 Ann Bot. 2016 Apr; 117(4):607-23. doi: 10.1093/aob/mcw008. Epub 2016 Mar 8" |
