Abstract: Relat ionship between Ca2+ localization and change in the fruit flesh cells and cell ultrastructure during fruit development of pear ( Pyrus pyrifolia Nakai) cv. kosui were studied using the cytochemical method of antimonite precip itation technique. The results showed that before the fertilization no Ca2+ sediment particles could be detected in the flesh cells and there existed little chromat in and light staining was observed in the nucleous. After fertilization many Ca2+ sediment particles could be detected in the flesh cells, mainly distributed in nucleus, cytoplasm, plastids and exterior membrane of chloroplast . The plastids containing Ca²⁺ expanded great ly. In addition, Ca²⁺ sediment part icles could be observed in vessels and primarily developed stone cells. It was found that Ca²⁺ moved to the linking space in between the fruit flesh cells one week after fertilizat ion. There was little or no Ca²⁺ in the cells and vessels of physiologically dropped fruits, whereas Ca²⁺ was distributed along the vacuolar membrane of some cells. Three to fourweeks after the fertilization it was difficult to detect the Ca²⁺ sediment part icles in the flesh cells, which continued unt il the fruits were harvested. However, Ca²⁺ sediment particles appeared in both sides of flesh cell wall before the fruits rotted. Relationship between function of Ca²⁺ in fruit development and ultrastructure is discussed herein.

Key words: Pear, Fruit development, Localization of Ca²⁺