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Toxic effect of iron on green and brown hydra (Hydra viridissima and Hydra oligactis Pallas)

Iron is among the mo t common metals in Earth's crust. Hydra is a freshwater animal that belongs to the phylum Cnidaria. Toxic effect of iron on various organisms has been researched before but this is the first documented research on its effect on hydras. Green hydra contains symbiotic algae in its gastrodermal myoepithelial cells. Individuals of symbiotic green hydra were treated with six concentrations of aqueous solution of iron dextran, while aposymbiotic brown hydras were treated with 14 concentrations of aqueous solution of iron dextran ([C6Hlo03ln[Fe(OH)3]m) for three days. The following morphological changes were monitored by stereolupe: migration of individuals in experimental dish, changes of body shape, reaction to mechanical stimuli, tentacle reduction, mucous secretion and asexual reproduction. Migration of hydras was the first step in evading deleterious microenvironmental conditions, followed by changing its body shape. AI lower concentrations of iron some green hydra individuals budded, expressing the horme tic effect. The secretion of mucous, a mechanism for removal of toxins, was observed. High concentrations of iron caused morphological and histological changes and mortality. Histological changes were observed by light microscope Nikon Eclipse E600 and software for morphometric analysis of histological images LUCIA G 4.80 Morphometric analysis included measuring of endoderm and ga troderm segments area and mesoglea thickness. For histochemical detection of iron depo itions in hydra tissue, we used Pearls' Prussian Blue method. Iron depositions in hydra tissue were observed as blue staining within cells (Figure 1). Thickness of mesoglea (jlm) was determined morphometrically by randomly choosing 150 different spots of variou thicknesses at iron concentrations of I mg/L, 400 mg/L, 1400 mg/L and 1500 mg/L, and in control group. Surface of 15 ectoderm and gastroderm segments (J.lm2) measuring 100 jlm in length, at same concentrations of iron was also measured. Iron was deposited in ectoderm and gastroderm of hydras. Damage to the cell layers increased with increasing concentrations of iron. There were no iron depositions in mesoglea, but its thickness increased during the treatment. Green hydra showed a higher level of resistance in surviving the unfavorable conditions of microenvironment than brown hydra. Symbiosis was pointed out as an evolutionary advantage.

hydra; iron; toxicity

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