Abstract: The cytochemical localization of ATPase in differentiating and mature phloem cells of broad bean (Vicia faba L. )has been studied using a lead precipitation technique. The phloem of the recurrent vascular bundle of broad bean seed coat contains a considerable number of plasmodesmata, which is benefit for symplastic unloading, and also exhibits ATPase activity in the plasma membrane of sieve elements and companion cells,through which photoassimilates unload apoplastically. The phloem of the complete chalazal vascular bundle persistently exhibits high ATPase activity in the plasma membranes of sieve elements and companion cells and in the plasma membrane of developed transfer cells. It shows that apoplastic unloading is the main pathway of unloading. The epidemic cells of cotyledon transform to typical transfer cells exhibitting strong ATPase activity in the plasma membrane. The photoassimilates actively are transported into the cotyledon passing through the membrane apoplastically.

Key words: Broad Bean, Seed Coat, Pholem, Localization of ATPase, Unloading