INTRACELLULAR SYMBIOSIS OF A PHOTOSYNTHETIC PROKARYOTE, PROCHLORON SP, IN A COLONIAL ASCIDIAN

摘要

Cells of a symbiotic prokaryote, Prochloron sp., in colonies of a tropical ascidian, Lissoclinum punctatum, occur not only outside but also inside cells of the host. Cells of these photosynthetic symbionts of ascidians have previously been reported only extracellularly. The intracellular and extracellular symbionts do not differ morphologically. The host cells carrying the symbionts are freely distributed in the ascidian tunic. They probably endocytize the symbionts and then retain them within a vacuole. Since the intracellular prokaryotes showed no evidence of rejection or degeneration, this association between tunic phagocytes of L. punctatum and cells of Prochloron sp. seems to constitute a stable symbiosis, comparable to the postulated ancestral association between heterotrophic cells and the photosynthetic prokaryotes which gave rise to chloroplasts. [References: 26]