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Symbiotic and asymbiotic hydras and algae in a toxic environment

The effect of norflurazon on symbiotic green hydra (Hydra viridissima Pallas, 1766/strain S1J-J1), and asymbiotic brown hydra (Hydra oligactis Pallas, 1766/strain S1M-K1) and green alga Chlorella kessleri Fott et Novak. [K&H, 1992] was researched. Norflurazon is a selective translocational herbicide that causes &laquo ; bleaching effect&raquo ; upon the newly developed chloroplasts, resulting in the decrease of the viability of the organism. Green hydra is a typical example of endosymbiosis. In its gastrodermal myoepithelial cells it contains individuals of Chlorella sp. In ecotoxicological research, this was the first example of such a series of test-organisms, which share the complex evolutionary and symbiotic relationships. The organisms were treated under both high- and low-light conditions for 21 days with five concentrations of aqueous solution of norflurazon (2x10-4, 2x10-5, 2x10-6, 2x10-7 and 2x10-8 mol/L ; SAN 9789, Sandoz Ltd., Basel, Switzerland) in the laboratory conditions. Conventional histological and TEM methods were used. Higher concentrations and high-light conditions caused increased mortality, significant morphological, cytological, histological and ultrastructural changes, changes in behavior, locomotion and asexual reproduction in all the test-organisms. Damages to aposymbiotic organisms were much more expressed than in the symbiotic organisms. In low concentrations of norflurazon, the similarity to the control and hormestic effect upon the algal growth was manifested. Well defined green hydra endosymbiosis was disturbed. Of special significance were antichloroplastal and antimitochondrial effects, as well as damages to almost all the organelles of the organisms. Newly developed buds in green hydra were not bleached, while the bleaching effect was present only in the algae out of the symbiosis. Symbiotic relationship in green hydra was confirmed firm and stable. The final result of the disturbed symbiosis between hydra and alga was the reassembling of the endosymbiosis in particular individuals that survived, as well as their partial or full recovery. By analyzing the green hydra symbiosis in itself, symbiotic Chlorella performed as the stronger link in this symbiotic relationship. Endosymbiotic alga was less affected by intoxication than green hydra itself. Hydra suffered from overall greater percentage of damages than the alga. It can be concluded that symbiosis provides greater survival potential in a toxic environments and represents an evolutionary advantage. It appears that complex symbiotic relationship as a result of pre-adaptations blocks the bleaching effect in green hydra. When it came to survival, symbiotic alga seemed to present the stronger component of the green hydra symbiosis. Instead of the usual cooperation between two endosymbiotic partners, in a sense alga performed a cheating mechanism in a toxic environment.

symbiosis; aposymbiosis; green and brown hydra; Chlorella; norflurazon; ecotoxicology

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