Research On The Degradation Of Cell Wall Polysaccharides And Relevant Enzymes During Plum Fruit Softening

Plum fruits were used as materials to study the degradation character of cell wall polysaccharides during on-tree ripening, as wall as the effects of endogenetic ethylene and cell wall degradation enzymes on plum fruit softening.The results showed that:1) The modifications of ethylene production, firmness were determined in present study. The maximal ethylene productions of plum fruit were posterior to the rapidly change of fruit texture, the results showed that ethylene not the main reason of the rapidly softening of the plum fruit.2) The results of the analysis of Amounts of polyuronide and neutral sugar showed: The amount of polyuronide had no change in Na₂CO₃-1and Na₂CO₃-2 pectin, then declined in later stages, commensurate with the increase in CDTA-soluble pectin. This suggested that in later stages an increasing proportion of the covalent bonds and holding some pectin polymers in the wall were broken, pectin solubilisation, so that their only asssociations with the wall were by ionic cross-links.The amounts of matrix in KOH-1 and KOH-2 declined during plum fruit ripening and programmed fruit softening.3) The results of the analysis of sugar compositions of cell wall polysaccharides determined by gas chromatogram showed that, the cell wall content of neither Ara nor Gal showed any decline during plum ripening,only loss in a loosely attached fraction soluble in KOH in later stages.The loss of neutral sugars in hemicellulosic polysaccharides had significant effect on plum fruit softening during on-tree ripening.4) The changes of the activities of polygalacturonase, pectin methylesterase,β-D-galactosidase and cellulase were studied during plum fruit on-tree ripening. Polygalacturonase (PG) activity was largely responsible for pectin depolymerization and solubilization in later stages, but PG mediated pectin depolymerization requires pectin to be demethylesterified by pectin methylesterase (PME).Cell wall swelling may be related to the xyloglucan–cellulose network and to pectin solubilisation, and these processes combined with the loss of pectic side chains. An increase in wall porosity in later ripening stage may allow increased access of degradative enzymes to their substrates.