engleski

The Effect of Norflurazon on Green and Brown Hydra

The effect of norflurazon on green and brown hydra was studied on ecotoxicological and evolutionary level. The aim was to compare changes between two closely related hydra species, to trace differences of the effect of herbicide upon them and to draw out the conclusion about sustainability and advantage of hydra symbiosis. Green hydra (Hydra virdissima Pallas, 1776) is a typical example of symbiosis (1). In its gastrodermal myoepithelial cells it contains the individuals of unicellular green alga Chlorella (Fig. 1, (3)). Brown hydra (Hydra oligactis Pallas, 1766) is a nonsymbiotic hydra. Herbicide norflurazon (nf) causes chloroplastal bleaching. Individuals of green (sort S1J-J1) and brown (sort S1M-K1) hydra were treated with five concentrations of aqueous solution of norflurazon (2x10^-4, 2x10^-5, 2x10^-6, 2x10^-7 and 2x10^-8 mol/L ; SAN 9789, Sandoz, Switzerland) in the laboratory conditions (21o C, photoperiod 10 h daylight and 14 h dark) in subacute exposure for 21 days. They were compared to the control groups of organisms. For morphological analysis binocular light microscope Carl Zeiss, Jena was used. For cyto-histological analysis hydras were fixed in Bouine fixative 24, 48 and 72 h after the beginning of the experiment. Preparations were dyed with 0.1% toluidine blue pH 4.4 and hämalaun-eosine (he). Micrographs were made by using Reichert and Nikon Eclipse E600 microscopes, Pentax and Nikon DXM1200 cameras. Nf toxicity resulted in numerous structural changes, showing the strong deleterious effect upon both hydra species, damaging almost all their structures. Depending on the concentration, nf affected viability and caused mortality, significant morphological, cyto-histological changes, changes in locomotion, behavior and asexual reproduction. In all parameters brown hydra showed higher nf susceptibility. Most prominent damages to the animal cells were apocrine secretion around the animal body and damages to ectodermal and gastrodermal myoepithelial cells. Glycocalyx was partially missing. Gastral cavity was filled with different cellular components. I- and zymogene cells were in the process of dedifferentiation to other cell types and migration across the body axes (Figs. 2-4). Endosymbiotic algae fell out of their host cells. They were reduced in number, changed in shape, size and color and chloroplastal degradation was present. Newly developed buds were not bleached. The final result of the disturbed symbiosis of green hydra was the reassembling of the endosymbiosis in particular individuals that survived, as well as their partial or full recovery. Since there was no bleaching noticed, it seemed that the symbiotic interactions, which are the result of symbiont's preadaptations, block the chloroplastal bleaching in green hydra. Therefore it could be concluded that endosymbiotic Chlorella from green hydra could perform some level of resistance to toxicants (2). This result could support the ever-stronger idea that Chlorella from green hydra represents a separate species of algae (4). Also, as brown hydra showed higher level of nf susceptibility than green hydra, symbiosis confirmed to present the evolutionary advantage. Research in this field contributes to resolving and better understanding of the complex problematic of symbiosis in fundamental biological science.

hydra; norflurazon; symbiosis

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