An Ultrastructural Study of the Azolla — Anabaena Azollae Relationship

Abstract

Light- and electron-micrographs reveal the following aspects of the organization and ultrastructural characteristics in the relation between Azolla pinnata and Anabaena azollae. Particular attention was paid to leaf cavity formation and the association of algae with hair cells during leaf development. The findings reveal that the stem tip is the site of initiating the infection of the plant by algae. A large increase of the leaf cavity occurs in the young leaf. Then, the algal filaments fill the cavity completely. The subsequent development of the leave shows enlargement of the leaf cavity with the algae lining the leaf cavity. Some pictures show that the algae form a slime layer covering the wall of the leaf cavity. The plant cells produce hairs protruding through the slime layer into the cavity. The hairs can contain one, two or more cells. But usually they consist of two or more cells. At most stages of development, the Anabaena cells are associated with hair cells. The hairs produce labyrinthine wall ingrowths and have cytoplasm with numerous organelles. Many of them appear to be high vacuolated and filled with a dense substance. The new hairs initially appear as a small bud on an epidermal cell which then undergoes a transverse division. This morphology and ultrastructure of the hair cells demonstrate and support the notion that they may either have a function in absorption of algal metabolites or in the possible metabolic interchange between Azolla and Anabaena azollae (Duckett, Toth and Soni, 1975).