PECULIARITIES OF THE SYMBIOTIC SYSTEMS OF PROTISTS WITH DIVERSE PATTERNS OF CELLULAR-ORGANIZATION

The analysis of symbiotic systems' occurrence in the representatives o f several protists' macrotaxa with various patterns of cellular organi sation (amoebae, flagellates and ciliates) has been performed. The fre quency of symbionts' occurrence in different cell compartments has bee n evaluated on the basis of data obtained from literature and original electron-microscopical investigations. Cell coat, cytoplasm, perinucl ear space, karyoplasm and various cell organelles has been studied. No reliable cases of symbionts' maintenance in protists' mitochondria an d plastids were established. The occurrence of symbionts' associations in different taxa varies essentially. Symbiotic systems of three prot ists' groups analysed are shown to possess qualitative differences. In amoebae (Lobosea, Gymnamoebia) in 24 species out of 61 species studie d symbionts are found in cytoplasm only; they are maintained neither o n the cell coat nor in the nucleus and other organelles. Symbiotic sys tems of flagellates and ciliates in general have much in common. For e ach of these groups more than a hundred species of symbionts are descr ibed. Symbionts occupy the cell surface, cytoplasm, karyoplasm and per inuclear space. For different ecological groups of flagellates high fr equency of occurrence of various symbionts on the cell surface is note d (in more than 30 species), reports of ectobionts in ciliates being l ess numerous and mostly restricted to metanobacteria. The results of a nalysis performed show that the formation of symbiotic relationship in lower eukaryotes' evolution is not a partial result of accidental anc estral partners' combinations. It is a natural phenomenon, widely dist ributed of protists. It is pronounced in diverse forms and with variou s frequency in different evolutionary branches. We suppose that the re gularities of appearance of stable symbiotic associations are determin ed by the pattern of cellular organisation of the host to a great exte nt and depend upon the morphophysiological preadaptations of prokaryot ic microorganisms trying to use the protists' cells as their environme nt in the course of their co-evolutionary process.