Abstract

The intracellular symbiosis of leafhoppers is the first system in which the morphological description is extended to understand the principles of symbiosis on a molecular level. Host, symbionts and environment exist in mutual dependence with respect to pH, osmotic pressure, inorganic and organic substances. Symbionts function primarily as mediators between host and environment. They became integrated in the course of evolution, enabling the host to adapt to changing nutritional and other environmental conditions. Comparison with other symbiontic systems shows that this seems to be a general principle.According to the endosymbiontic theory of eukaryotic cells, this is true also for mitochondria, chloroplasts, and possibly other cellular organelles. Thus, the intracellular organelles and the endosymbionts appear to represent functions of the same principle on a different level of integration. This can be interpreted as support for the endosymbiontic theory of eukaryotic cell