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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.

Aluminum (Al) is one of the most abundant chemical elements in the Earth's crust. Yet, the effect of Al on living beings was little known until recently. This was partly because Al becomes soluble in water with increasing acidity only, and it was essentially harmless until acid rains first appeared. Because it is possible for the Al to be a major constituent of surface and subterranean waters, thereby presenting a potential environmental danger for freshwater organisms, the aim of this research was to compare the changes between two closely related hydra species. Specifically, we sought to trace differences and the extent of damage of the effect of Al upon green and brown hydra. Usually found in unpolluted freshwater, hydra is in the the phylum Cnidaria. It has a simple, cylindrical body with an adhesive foot on one end and a mouth surrounded by five to eight tentacles on the other. It comprises two cellular layers separated by mesoglea. Green hydra forms a symbiotic relationship with Chlorella algae. Hydra has a tremendous rate of regeneration. A comparative static toxicity test was performed using the individuals of green (Hydra viridissima Pallas, 1766 ; strain S1J-J1) and brown (Hydra oligactis Pallas, 1766 ; strain S1M-K1) hydra. They were treated with 9 concentrations of aqueous solution of aluminum sulphate (25, 50, 80, 100, 150, 200, 250, 350 and 500 mg/L ; Kemika, Croatia) in laboratory conditions (22.8oC) in subacute exposure for three days and compared to the control groups of organisms. After the exposure, the animals were put in clean aquarium water, and left recovering for 14 days. Al toxicity triggered numerous morphological and behavioral changes, showing the strong deleterious effect on both hydra species. Brown hydra showed higher Al susceptibility in all parameters. Higher concentrations triggered more prominent changes: tentacle reduction, incoherent and sluggish reactions to mechanical stimuli, migration towards water surface and apocrine mucous secretion of ectodermal layer. It strongly induced a hormestic effect in the asexual reproduction of green hydra and even induced sexual reproduction. Mortality was noted only in the highest concentration. An interesting hypothesis was confirmed wherein the brown hydra was able to regenerate itself to its original height by elongating its epithelial cells. This ability in the green hydra is yet to be examined. Control animals did not show any changes. As brown hydra showed higher level of Al susceptibility than green hydra, symbiosis seemed to present an evolutionary advantage. Higher water acidity levels greatly increased the overall toxicity of aluminum to these species. Greater Al concentrations brought harmful impact to both species. However, cooperative ad symbiotic interactions between the green hydra and the green algae give the symbiont stronger and better resistance compared to the brown hydra. This hydra bioassay was shown to be a useful tool for quick corroboration of the expected results.