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Abstract:
The leafhopper Euscelis incisus K (Homoptera) hosts two types of obligate intracellular symbionts (endocytobionts). The DNA molecular weight (approximately 10(8)) of endocytobionts corresponds to that of the mitochondria and plastids. They are transmitted to the next host generation by incorporation between the egg coat and egg cell in the form of an infection mass. Excision of the infection mass results in cephalothorax embryos which lack the abdomen. Endocytobionts synthesize metabolites such as vitamins, amino acids for the hists using their waste products such as urea and uric acid. The endocytobionts regulate pH, osmotic pressure and certain endogenous rhythms of their hosts. This implies that the leafhopper endocytobionts represent for the host cell not only nutrition but also genomic supplement. According to this hypothesis, the structure, function and information of endocytobionts and eukaryotic DNA-containing cell organelles are analogous; these analogies indicate that endocytobionts may provide a model for molecular analysis of eukaryotic cell system. "Endocytobiology" consequently represents a modern field of research between symbiosis and cell biology.