Poster: Cell Walls

Abs # 1247: A nascent pectin-xyloglucan complex formed in the pea Golgi apparatus: Arrangement of a newly-formed 1,4-b-D-galactan attached to a pectin-xyloglucan complex in peas.

Presenter:	Abdel-Massih, Roula M, rma00@hotmail.com
Authors	Abdel-Massih, Roula M (A) (B)  Baydoun, Elias A-H (A)   Brett, Chris T (B)
Affiliations:	(A): Biology Department, American University of Beirut, Lebanon (B): Institute of Biomedical and Life Sciences, Glasgow University, UK

Particulate enzyme preparations were prepared from etiolated pea epicotyls and used to assay for 1,4-b-D-galactan synthase using UDP-[U-¹⁴C]-galactose. The nature of the products formed was determined by selective enzymic degradation, gel permeation chromatography and anion-exchange chromatography (Abdel-Massih et al, 2003). The 1,4-b-D-galactan synthase transfers galactose residues to a large macromolecular complex containing galactan, rhamnogalacturonan I, polygalacturonic acid, and xyloglucan (XG). The links between XG and pectin appear to be covalent since there was no change in elution behaviour when passed through a column in presence of 8M urea or under high temperature treatment (70ºC). Complexes containing all these components have recently been found in some cell walls (Thompson and Fry 2000). An early model of sycamore cell walls proposed a linkage between the reducing end of xyloglucan and the arabinogalactan side-chains of pectin (Keegstra et al, 1973), and a similar structure might be present in the complex obtained in our system. However, it is hard to see how such a complex would be decreased in size by several orders of magnitude by the degradation of the xyloglucan component, as appears to be the case in our experiments. An alternative possibility, which fits our data better, is that xyloglucan forms the backbone of the molecule, since the products of endo-1,4-b-D-glucanase digestion can be further degraded by pectin-degrading enzymes. Abdel-Massih RM, Baydoun EA-H, Brett CT (2003) Planta, 216: 502-511. Keegstra K, Talmadge KW, Bauer WD, Albersheim P (1973) Plant Physiol 51:188-196. Thompson JE, Fry SC (2000) Planta 211:275-286.