Resistance to heavy metal toxicity in organisms under chronic exposure.

The rate of changes of heavy metal ions concentrations in the organism or biological system will determine the choice of strategy of realization of heavy metal ions effect and, consequently, the biological effect itself. Which of the possible strategies will dominate, depend on the rate of changes of concentration of heavy metal ions in biological systems, functional activity of organism at the moment of metal action and on metals chemical properties. Keeping this view, the present review deals with the concept of time-based alterations of concentration of heavy metal ions (TACMI) in biological systems. On the basis of TACMI concept formation of organism resistance to metal ions action could be explained. In the event of slow increase of its concentration in organism, it produces induction of metallothioneins, other stress-proteins and relative changes in the whole metabolic system. This, first of all, results in formation of new specific epigenotypes, which provide higher resistance (hormesis effect) not only to metal ions that induced this effect, but also to such stress-factors as high temperature (at least, for micro-algae cells).