柿果实采后软化过程中细胞壁组分代谢和超微结构的变化

Changes in Cell Wall Component Metabolism and Ultrastructure of Postharvest Persimmon Fruit During Softening

柿果实采后果胶酯酶活性迅速上升,其活性与果实硬度的下降呈明显的负相关。多聚半乳糖醛酸酶活性增加缓慢,但其活性与果实硬度的下降无明显相关性。β-半乳糖苷酶活性迅速增加,其活性与果实硬度的下降呈明显的负相关。纤维素酶活性呈逐渐上升趋势,与果实硬度的下降也呈明显的负相关。伴随着细胞壁水解酶活性的增加,果实原果胶和纤维素含量迅速下降,而水溶性果胶含量则迅速上升。柿果刚采收时细胞壁结构完整,3d后细胞壁中胶层基本被溶解,甚至初生壁也局部发生降解。

The changes in cellular wall hydrolases, cellular wall components and cellular wall ultrastructure of postharvest persimmon （Diospyros kaki L. cv. Bianhua） fruit during softening were studied. Pectinesterase activity increased sharply at first and reached a peak （Fig. 3A）. Significant correlation was observed between the pectinesterase activity and the loss of flesh firmness （r=-0.74）. Polygalacturonase activity increased slowly （Fig.3B）, but there was no significant correlation between the polygalacturonase activity and the loss of flesh firmness. β-galactosidase activity increased sharply （Fig. 3C）, with a negative correlation between the β- galactosidase activity and the loss of flesh fruit firmness （r=-0.77）. Cellulase activity increased markedly during ripening （Fig.3D）. Significant correlation was observed between cellulase activity and the loss of flesh firmness （r=-0.90）.Consistent with the increases in activity of cell wall hydrolases of cell wall constituents, fruit softening was accompanied by a progressive increase in WSP （water soluble pectin） content and a progressive decrease in protopectin and cellulose content （Fig.4）. The cell wall structure was integrated when persimmon was harvested （Fig. 5A）. After 3 d of ripening, the middle lamella became liquefied （Fig.5B）, or even the primary cell wall was dissolved in some regions （Fig.5C）.