ANABAENA-AZOLLAE AKINETES IN THE SPOROCARPS OF AZOLLA-FILICULOIDES LAM

At the present time the taxonomic position of the cyanobacterium symbiont of the aquatic fern Azolla is still controversial. Usually it is reported as Anabaena azollae Strasb, but recently Komareck and Anagnostidis have assigned it to Trichormus azollae (Strasb.) Kom. and Anagn. Various attempts to clarify the identity of this microorganism is difficult due to the lack of information regarding the akinetes, whose developmental pattern represents a diacritic character for the Nostocacean taxonomy. The object of this study was to examine the akinetes in the sporocarps of two strains of Azolla filiculoides. Akinetes were examined using a light and a fluorescent microscope equipped with different filters and their ultrastructure was determined by TEM and SEM. Akinetes and mainly rod shaped bacteria were found under the indusium of the sporocarps. The akinetes appeared in chains without interspersed vegetative cells and they were embedded in a film of mucilagenous material. A multilayer envelope was evident and the cells contained cyanophycin, glycogen, chlorophyll and phycobiliproteins. Differences in pigment content and ultrastructure have been detected between the akinetes present in the megasporocarps and microsporocarps. In the latter the Anabaena cells had lower contents of chlorophyll. Based on the developmental patterns and morphological characteristics the assignment of the Azolla endophyte to Trichormus azollae Kom. and Anagn. appears to be acceptable.