Effect of Wounding on Hydroxyproline Content and Its Distribution in Cell Wall of Some Vegetables

Abstract

Wounding is one of undesirable phenomena during post-harvest handling and storage of vegetables, because it causes their deterioration. The changes in the hydroxyproline content and its distribution in cell walls of vegetables were investigated to clarify the effect of wounding on changes of cell wall components. The hydroxyproline content in cell walls of wounded vegetable increased during incubation at 20°C. The increase ratio of hydroxyproline by wounding was found in the order; potato>cucumber>Japanese radish>sweet potato>tomato>turnip>lotus root>pumpkin>sweet pepper>carrot. The hydroxyproline of sweet pepper was distributed in pectin, hemicellulose I, hemicellulose II and cellulose fractions in the cell wall. The hydroxyproline content in hemicellulose I fraction was more than that in the other fractions. Both hydroxyproline and protein contents were increased in every fractions of the cell wall by wounding, suggesting that the hydroxyproline-containing proteins are increased in all fractions of the cell wall by wounding. Although the amino acid composition of the hemicellulose I fraction was similar to that of the hemicellulose II fraction, the percentage of hydroxyproline was higher in hemicellulose II fraction than in hemicellulose I fraction. Moreover, the percentage of hydroxyproline in hemicellulose II fraction was slightly increased by wounding. The hydroxyproline/protein ratios in hemicellulose II and cellulose fractions tightly bound to the cell wall were increased by wounding, but those in pectin and hemicellulose I fractions weakly bound to the cell wall were not increased. Therefore, it is suggested that wounding induced more strongly the linkage of hydroxyproline-containing protein to the cell wall with passage of time.