Metabolic relations and intercellular signals in the anabaena-azolla association

The symbiotic interaction between the water fern Azolla and its nitrogen-fixing cyano- biont Anabaena is characterized by an efficient exchange of metabolites between the partners. The host provides photosynthates to the cyanobiont present in the leaf cavity of the fern, and fructose is actively taken up by the isolated cyanobiont, which leads to enhanced heterotrophic metabolism, heterocyst differentiation, and nitrogenase activity. A soluble extract of Azolla was shown to enhance sucrose uptake and sucrose-supported growth of Anabaena. The interaction between the symbiotic partners involves molecular interactions between surface molecules and their counter-receptors. Such interactions are suggested to facilitate metabolite exchange.