1983 Volume 52 Issue 3 Pages 250-255
The cellular breakdown in watercore tissue of the Japanese pear was investigated by identifying the change in cell wall polysaccharides and their constituent monosaccharides, and by tracing cell wall-degrading enzyme activity.
The activity of xylanase and arabanase, which degrade hemicellulose components, increased more watercore tissue than in healthy tissue during the initial stage of the disorder (grade 1-2), but a rise in activity was not observed during the severe stages (grade 3-4 and 5-6). The activity of the other hemicellulases (β-xylosidase, β-glucosidase and β-galactosidase) showed little difference between healthy and damaged tissue. On the other hand, increases in the neutral form of endocellulase activity at grade 1-2 and in polygalacturonase activity at all grades were prominent in the watercore tissue, as observed in a previous paper(5).
In the watercore tissue, the breakdown of the cellulose component was the most prominent among all of the cell wall polysaccharide components. That is, the cellulose component had already begun to decrease at grade 1-2, and was further reduced at the more severe stage of the disorder to about 85% and 75% of the cellulose in healthy tissue at grade 3-4 and 5-6, respectively. Acid soluble-hemicellulose components also decreased at grade 3-4 and 5-6. However, there were no differences in the alkali-soluble hemicellulose components between healthy and damaged tissues. This tendency resembled the cell wall degradation pattern observed in over-ripe fruit. Thus, the watercore in the Japanese pear seems to arise from the fact that some parts of the fleshy tissue ripen faster than other parts.