Charaterization of a crosslink between Xyloglucan and Rhamnogalacturonan from cotton cell walls

Abstract

Pectin is the most complex and major component of primary plant cell walls. For better understanding of its structural complexity and heterogeneity, it is crucial to know about the structure and linkages within the pectic regions as well as to other polysaccharides present in primary cell walls. Our main aim is to characterize the cross-linkage between the XG and RG. Preliminary results show nearly half of the XG is covalently linked to RG. EPG digestion of cell walls followed by strong alkali extraction (24 % KOH & 0.1 % NaBH4) solubilizes most of the XG-RG complex along with other pectic polysaccharides and unlinked hemicelluloses. The XG-RG complex can then separated from the neutral and slightly acidic sugars using ion exchange chromatography. Treatment with arabinosidase removes the arabinose from the arabinan in the XG-RG complex. Free arabinose can be separated using an ion exchange column. Further treatment of the complex with arabinanase, cleaves the arabinan linkages essentially dissociating most of the XG from RG. These finding were supported with sugar composition, CZE electropherograms, MALDI-TOF MS spectra, and NMR spectroscopy. Our experimental results significantly suggest arabinan being the crosslink present between the XG and RG complex as proposed in an earlier plant cell wall model by Keegstra et al.