Objective  Factors contributing to the distinctively different texture of the fruits of two pear cultivars were investigated.

  Method  Cellular microstructures of the pulp of Yuluxiangli and Daguoshuijingli pears were observed under an electron microscope SU810 . Textural firmness and brittleness, as well as contents of cell wall-modifying enzymes and relative expressions of the associated genes, of the fruits during develop stages were measured to correlate with the microstructure observations.

  Result  ①The firmness of the pears of both varieties gradually declined during the fruit development. The force required to break into the fruit decreased 60d after flowering as the fruits were ripening. In comparison, Yuluxiangli pears were significantly softer and less brittle than Daguoshuijingli. ②At 400× magnification, the cells of Yuluxiangli pear pulp appeared larger than those of Daguoshuijingli at young stage. As the fruits expanded and matured, the cells of both varieties enlarged significantly but those of Yuluxiangli became smaller than those of Daguoshuijingli. And upon cutting, the edge of fractured Yuluxiangli pears were clean and smooth, while that of Daguoshuijingli rough and irregular. ③ In the matured fruits, the pectin methylesterase (PME) activity in Yuluxiangli pears were extremely significantly lower than that in Daguoshuijingli, whereas the polygalacturonase (PG) and β-galactosidase (β-Gal) activities extremely significantly higher. ④ The relative expressions of PME, PG, and β-Gal in Yuluxiangli were extremely significantly lower than those in Daguoshuijingli during the fruit development. And that of β-Gal was significantly positively related to the textural firmness, but that of PG to the brittleness, of the fruits for both pear varieties.

  Conclusion  The unique texture of Yuluxiangli and Daguoshuijingli pears could not only be differentiated by their pulp cell ultrastructural differences but also closely related to the cell wall-modifying enzymes, such as, PG and β-Gal, in the fruits. Hence, the genes associated with those enzymes likely played a critical role in the texture of the pears.