Protective role of metallothionein during regeneration in Eisenia andrei exposed to cadmium.

Lumbricid earthworms are often exposed to simultaneous action of various environmental stressors like soil contamination, temperature fluctuation or predators' attacks, which may induce extrusion of coelomocyte-containing coelomic fluid or loss of tail segments. If the injuries are not lethal, renewal of the immune-competent cells and soluble components of coelomic fluid and/or the regeneration of tail segments occurs. The aim of our investigations was to test the hypothesis that exposure of adult earthworms Eisenia andrei to cadmium-polluted soil at room temperature (RT) and/or low temperature (6°C) have adverse effects on restoration of experimentally depleted coelomocytes or on regeneration of amputated posterior segments. Intact control earthworms and their experimental counterparts subjected to electrostimulation-induced coelomocyte depletion or surgical amputation of posterior segments were maintained either in control soil or in soil spiked with cadmium chloride (500mg/kg air-dried soil) at RT or 6°C. Four weeks after the beginning of experiments, cadmium accumulation in earthworm bodies was significantly lower at 6°C than at room temperature. The numbers of restored cells and fluorophore contents were hardly affected by temperature or cadmium. However, cocoon production was reduced by cadmium and completely abolished at 6°C and regeneration of amputated posterior segments was inhibited in cold but was enhanced by cadmium exposure at RT. Independently on the temperature, the 4-week cadmium exposure of adult earthworms was connected with significantly upregulated expression of Cd-metallothionein (but not of catalase, lysenin and phytochelatin) in coelomocytes.

Exposure of Eisenia andrei (Oligochaeta; Lumbricidea) to Cadmium Polluted Soil Inhibits Earthworm Maturation and Reproduction but not Restoration of Experimentally Depleted Coelomocytes or Regeneration of Amputated Segments.

Lumbricid earthworms are often exposed to polluted soil. They are also commonly subjected to various stimuli and attacks by predators that induce extrusion of coelomocyte-containing coelomic fluid and/or the loss of body segments followed by the renewal of immune-competent cells and regeneration of tissues/organs. The aim of our investigations was to test the effects of exposure of the earthworm Eisenia andrei to cadmium-polluted soil, combined with electrostimulation-induced depletion of coelomocytes (i.e. amoebocytes and chloragocyte-derived eleocytes) or the surgical amputation of posterior segments, on earthworm maturation, reproductive output, and regenerative processes. Experimental worms were maintained up to 7 weeks either in unpolluted soil or in soil spiked with cadmium chloride (500 mg/kg air-dried soil). In juvenile worms, sexual maturation (measured by clitellum formation) was delayed and cocoon production was inhibited in Cd-exposed worms. Coelomocytes were significantly depleted by electrostimulation and the kinetics of their recovery was similar in worms kept in clean and cadmium polluted soils, in both exposure conditions amoebocyte recovery was faster than recovery of riboflavin-storing eleocytes. In adult worms, soil cadmium exposure inhibited reproduction but, at macroanatomical level, had a negligible effect on regeneration of amputated posterior segments, visible only on histological cross-sections.

Effects of nickel, zinc, and lead-contaminated soil on burrowing rate and coelomocytes of the earthworm, Allolobophora chlorotica.

We have shown previously that stubby worms Allolobophora chlorotica are sensitive to environmental stress, including metal-polluted soil. In order to discern the mechanisms of this sensitivity, adult (clitellate) Al. chlorotica were exposed in the laboratory to soil samples soaked with water (control) or Ni (1 and 2 mg/kg), Zn (1.25 and 2.5 g/kg) or Pb (5 and 10 g/kg) chlorides. Worms avoided contact with metal contaminants by prolonging burrowing time in metal-soaked samples, especially in the case of lead. Higher concentrations of the investigated metals were lethal for worms. During a 3 week exposure to lower metal concentrations, nickel and lead readily accumulated in the bodies of worms while zinc was efficiently regulated. However, body weights and numbers of non-invasively retrieved free coelomocytes (consisting of amoebocytes and riboflavin-loaded eleocytes) were significantly lower only in zinc-exposed worms. We assume that zinc regulation in worm bodies is more energy-demanding than nickel or lead bioaccumulation, thus this might be responsible for inhibition of the body gain and diminution of immunocompetent cells in zinc-exposed earthworms. Alternatively, missing free coelomocytes may actually be involved in Zn trafficking and removal through nephridia and/or in the formation of multicellular brown bodies, since metal can unbalance host/bacteria relationships.