Nucleolytic activities and appearance of a new DNase in relation to nickel and manganese accumulation inAlyssum murale

Serpentine and non-serpentine plants of Alyssum murale, a nickel (Ni) accumulator plant, from North Greece, were studied in order to examine: (1) The ability of natural plants to accumulate metals; (2) the ability of their seedlings to tolerate increasing concentrations of Ni2+ or Mn2+ (0, 0.16, 0.32, 0.5 and 1 mmol/L), when grown in nutrient solution; (3) the activities and electrophoretic patterns of root and shoot DNases and RNases under the above conditions. Measurements of metal concentrations in serpentine and non-serpentine natural plants and the respective soils revealed: (1) Very low calcium (Ca)/magnesium (Mg) (∼0.16) ratio and high concentration of Ni in serpentine soil; (2) very high Ca/Mg (∼17) ratio and high concentration of manganese (Mn) in non-serpentine soil; (3) the ability of serpentine natural plants to accumulate Ni and the inability of plants of both serpentine and non-serpentine populations to accumulate Mn. A. murale plants grown in nutrient solution with increasing Ni2+ or Mn2+ concentrations showed a negative correlation between the Ni2+ or Mn2+ concentrations in the nutrient solution, and the chlorophyll concentration, shoot and especially root length. The accumulation of Ni2+ or Mn2+ in the plant showed a positive correlation with increasing Ni2+ or Mn2+ concentrations in the nutrient solution. Application of 0.5 mmol/L Ni2+ or Mn2+ resulted in the inhibition of DNase activities and the appearance of a new DNase form, in both root and shoot detected by electrophoresis in active ssDNA polyacrylamide gel. The new gel-extracted DNase showed nicking action against plasmid DNA and has been characterised as an endo-DNase. In contrast, electrophoretic patterns and RNase activities were unaffected. According to our studies on growth, both serpentine and non-serpentine plants of A. murale have a constitutive ability to tolerate and accumulate Ni2+ or Mn2+; they have similar DNase and RNase electrophoretic patterns and show a new DNase form under Ni2+ or Mn2+ stress. This is the first report on the response of nucleolytic enzymes under metallic elements hyperaccumulation.