| Apple texture is one of the most important quality properties that influence consumers acceptability of cultivar fruit. To determine the dominating factor of apple fruit texture, the changes of fruit weight, firmness and crispness of fruit of 8 apple cultivars were monitored, and scanning electron microscopy(SEM) was employed to further explore difference between the ultrastructures of fruit fracture surface during fruit growth in this work. Finally, the changes of cell wall substances, related enzyme activities and gene expression in apple fruit during development were researched. The main results are as follows:1. Firmness of the fruit of 8 apple cultivars gradually reduced during fruit development, and fruit texture obviously differed among cultivars during fruit ripening.2. SEM showed that there are differences in cellular structure of apple fruit flesh with different texture, which appeared in fruit expanding and peaked in fruit ripening. The broken edges of crisp cultivars were smooth and tidy, forming crisp fracture. While the cultivars with bad crispness presented zigzag cracks, leading to plastic deformation. Moreover, cells in firm fruit were in neat order and arrangement, having highly distributed contact area, but the cells were entirely separated in the soft cultivars. All these results suggested that different cellular structure may lead to different fruit texture.3. The crispness slightly increased while the firmness and the content of the cell wall substances showed a tendency to decrease during fruit development. In fruit ripening, the content of WSP in the crisp cultivar fruits was higher, while the cellulose content was obviously lower.4. Analysis of activities of 4 enzymes related to cytoderm development showed that high PG and β-Galase activities and gene expression were observed in crisp cultivars, which suggested PG and β-Galase may co-regulate the degradation of pectin and contribute to the formation of flesh texture. |
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