Abstract:

This study was targeted to investigate，by means of ultracytochemical localization，the distribution of Ca 2+ during different developmental stages of seed embryoinduced somatic embryogenesis of Xanthocera sorbifolia，i.e.，of nonembryogenic calli (NEC)，embryogenic calli，globular and torpedo embryoids. The results showed that the NEC had the lowest deposit of Ca 2+，which was largely distributed in cell walls and intercellular spaces. A marked increase in the level of Ca 2+ was observed in embryogenic cells，which were mainly localized in plasma membranes，vacuole membranes and cytoplasm. The Ca 2+ grains，deposited in plasma membranes during the globular embryoid stage，were large but with little substance. During the torpedo embryoid period，deposits of Ca 2+ increased significantly and were concentrated largely in the radicle and embryo tips. A clear thickening of the outside cell walls，where more Ca 2+ was deposited，could be found in the outermost layer of radicle cells. We speculate that Ca 2+ might be closely related to different developmental stages of cells in the somatic embryogenesis of X. sorbifolia.

Key words: Xanthocera sorbifolia, somatic embryogenesis, Ca 2+, ultracytochemical localization