ABSTRACT
This chapter provides a current view on the Azolla-Anabaena symbiosis, focusing on recent genetic and molecular analyses of its endosymbiotic partner, Anabaena azollae. Vietnam and China are the only countries known to have a long history of Azolla cultivation. Azolla reproduces both asexually and sexually. Sexual reproduction of Azolla is a most complex and improbable process that presents many fascinating challenges to developmental biologists. Vegetative reproduction of Azolla is an extremely efficient process. The sporophyte of the fern reproduces by fragmentation via an abscission layer that forms at the base of each branch. Azolla plants are triangular or polygonal in shape and bear deeply bilobed leaves and adventitious roots. The physiology of Azolla has been studied extensively by numerous workers in the last decade. The nitrogen-fixation capacity of the Azolla-Anabaena association has been demonstrated indirectly and directly (by use of 15N2).
