Most of the reports about interactions of metals with nucleic acids and their metabolism are based on studies with bacteria and animals. Information from higher plants is rather poor. Ernst (1980) cited an increase of the number of structural chromosome aberrations after cadmium treatment of Crepis capillaris seeds.
In general metals can interact directly or indirectly with nucleic acids. The numerous nucleophilic centres in nucleic acids are favourite binding sites for metal ions. The type and localisation of binding apparently depend on the metal considered. Induction of crosslinks between both DNA strands, single-strand DNA breaks and chelation or formation of complexes between DNA and metals were described (see Gebhart and Rossman, 1991, for a review). Similar reactions can also be expected between metals and RNA, thereby affecting the specific functions of the latter.
Besides these direct effects, metals can indirectly induce breaks in the DNA strand: depurination of DNA which can have mutagenic effects was reported to be induced by copper(II), nickel(II) and chromium(IV) (Schaaper et al., 1987). Generation of oxygen free radicals can also cause DNA damage. Exposure of DNA to oxygen free radical generating systems was found to induce extensive strand breakage and degradation of DNA (Halliwell and Gutteridge, 1984).
Effects of metals on the function of various enzymes involved in the nucleic acid metabolism can also indirectly contribute to alterations in the genetic information by affecting replication fidelity.
Finally, the activity of hydrolytic enzymes as ribonuclease and deoxyribonuclease was found to increase after in-vivo cadmium supply to Glycine max seedlings. These effects were considered as symptoms of cadmium accelerated senescence (Lee et al., 1976a; see section on enzyme induction).
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