Abstract: 【Objective】This study aims to reveal the development of segment membrane which contributes to citrus fruit mastication. 【Method】Using different citrus types (hybrid citruses including Ehime No. 30 and Nova, Okitsu Wase satsuma mandarin, navel oranges including Yuanfeng and Newhall, and pumeloes including Anjiang and Jiangyong), the main physiological and biochemical properties of segment membrane were analyzed by comparisons in tissue development and cell ultrastructure.【Result】The results showed that rough outside but smooth inside of segment membrane occurred in all citrus types. Obviously waxy layer grew on the inside of segment membrane under which one or two cell layers with thickened cell wall arranged neatly. Cell density decreased gradually from inside to outside in segment membrane. Occurrence of wax layer in the inside and morphological changes of cells under the wax layer emblematized the maturation of citrus segment membrane. For pomelo, the thickest segment membrane linked with the worst mastication was caused from a large number of cell layers, enlarged cell size and more pectin in segment membrane. At early fruit development from squaring stage to flower withering stage, ventricles differentiated already in the ovary and the intervals between ventricles would develop into segment membranes. In the period, parenchyma cells in the intervals exhibited equal cell size and arranged neatly, having no segment membrane characteristics. With fruit enlargement and maturation, segment membranes of Shatian pomelo had the most cell layers and the longest cell wall thickening period. Segment membranes of Shatian pomelo showed significantly higher pectin content than that of Yuanfeng navel orange and Juxiangzao Satsuma mandarin. Segment membranes of Yuanfeng navel orange had medium cell layers and moderate cell wall thickening period, in which protopectin was higher than that of Juxiangzao Satsuma mandarin. Segment membranes of Juxiangzao exposed the least cell layers and the shortest cell wall thickening period. In October when Juxiangzao matured, segment membrane protopectins in Shatian pomelo, Yuanfeng navel orange and Juxiangzao Satsuma mandarin were 364.22, 208.48 and 165.39 mg.g^-1 respectively, with Shatian pomelo reaching 74.7% and 120.2% higher than another two varieties. 【Conclusion】Segment membrane thickness, cell layers in segment membrane and degree of cell wall thickening associate with citrus fruit mastication. Pectin content could reflect the mastication of citrus segment membranes.

Key words: Citrus, Segment membrane, Mastication, Ultrastructure, Cell wall