Phytochemistry. 1975, Vol. 14, pp. 2213-2222. Pergamon Press. Printed in England. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJI ENZYMIC ANALYSIS OF CELL WALL STRUCTURE IN APPLE FRUIT CORTICAL TISSUE MICHAEL KNEE East Malling Research Station, East Malling, Maidstone, Kent ME19 6BJ. England and ANTHONY H. FIELDING, SIMON A. ARCHER* and FERNANDO LABORDA? Long Ashton Research Station, University of Bristol, Bristol, BS18 9AF zyxwvutsrqponmlkjihgfed (Revised Received 25 January 1975) Key Word Index--Ma/us domestica: Rosaceae; apple fruit; cell wall composition; polysaccharides; fungal glycanascs. Abstract-Galactanase from Phytophthora infestuns and an arabinosidase isoenzyme from Sclerotinia ji-uctigena attacked the cortical cell walls of apple fruits liberating galactose and arabinose residues, respectively. Other arabinosidase isoenzymes from S. jktigena attacked cell walls very slowly. A S.+uctigena polygalacturonase isoenzyme liberated half of the uranic acid residues with few associated neutral residues, while a second polygalacturonase isoenzyme released more uranic acid with a sub- stantial proportion of arabinose and galactose and lesser amounts of xylose, rhamnose and glucose; reaction products of this enzyme could be further degraded by the first isoenzyme to give high MW fragments, rich in arabinose with most of the xylose, rhamnose and glucose, and low MW fragments rich in galactose and uranic acid. Endoglucanase from Trichodermu uiride released a small proportion of the glucose residues from cell walls together with uranic acid, arabinose, xylose and galactose; more extensive degradation occurred if walls were pre-treated with the second polygalactur- onase isoenzyme. Endoglucanase reaction products were separated into a high MW fraction, rich in arabinose, and lower MW fractions rich in galactose and glucose residues. The high MW polygalac- turonase and endoglucanase products could be degraded with an arabinosidase isoenzyme to release about 75% of their arabinose. Cell walls from ripe fruit showed similar susceptibility to arabinosidase and galactanase to those from unripe apples. Cell walls from fruit, ripened detached from the tree were more susceptible to degradation by polygalacturonase than walls from unripe fruit or fruit ripened on the tree. Endoglucanase released less carbohydrate from ripe fruit cell walls than from unripe fruit cell walls. INTRODUCTION of purified enzymes to degrade sycamore suspen- Chemical degradation of apple fruit cell walls to yield fragments, which were separated by ion exchange chromatography and gel filtration and analysed for their monomeric composition, has given a partial account of their structure Cl]. Use sion culture wall polymers, and methylation analysis of fragments have contributed to a model of plant primary cell wall structure C2-43. The model embodies a pectic framework of a-1,4 linked galacturonic acid residues, interrupted by rhamnose residues, and having side chains of p- 1,4 galactosyl residues and branched ara- *Present address: Department of Botany, University of Bristol, Bristol, BS8 1UG. b’ man [2], which is also supported by other evi- t Present address: Department of Plant Pathology, Univer- dence f.51. The suggestion that xyloglucan is cova- sity of Wisconsin, Madison, Wisconsin 53706, U.S.A. lently linked at some point to this structure [3,4] 2213