Changes in cell wall of mango fruit during ripening

Abstract

Changes in cell walls and in the levels of polysaccharide-degrading enzymes, in mesocarp of mango fruit during ripening were investigated. Total, insoluble cell wall content declined with ripening. Galactose, arabinose, xylose and mannose were lost from the wall during ripening and autolysis of ripe mango mesocarp released arabinose and xylose into the soluble fraction. Galacturonic acid was also removed from the wall but polygalacturonase (which degrades pectic galacturonan in fruits of many other species) could not be detected. Several glycosidase activities were present in the mesocarp and, of these, a-d-galactosidase and mannosidase increased markedly during ripening. The increase in the former may be significant in the removal of wall-bound galactose accompanying ripening.Enzyme extracts prepared from ripe mangoes released galactose from cell walls isolated from unripe fruits but soluble polysaccharides released from the wall by enzyme action In vitro could not be detected by electrophoresis. Polysaccharides, composed mainly of xylose and glucose, were co-extracted with enzymic protein from mango mesocarp and there was evidence that these polymers underwent degradation during ripening. They may be derived, partly at least, from wall hemi-celluloses. It is proposed that one process contributing to cell wall breakdown and resultant tissue softening in the mango may be the enzymic hydrolysis of polysaccharides containing arabinose and galactose (possibly neutral pectic polymers) and that polygalacturonase activity probably does not contribute significantly to tissue softening The mechanism for removal of galacturonan from the wall was not established but this may result from prior removal of polysaccharides containing arabinose and galactose. Data obtained also suggest that hemi-celluloses in the wall may be degraded during ripening, Critical appraisal was made of the limitations of both preparatory and analytical methods employed and proposals made for employing better methods in further work.