Comparative Responses of a Copper-tolerant and a Copper-sensitive Population of Minuartia hirsuta to Copper Toxicity

Abstract

The response of two populations of Minuartia hirsuta with different copper tolerance to an excess of copper was studied. The population originatin from copper contaminated sites showed a distinct tolerance to copper. A more vigorous growth of copper tolerant plants under increasing copper concentrations was found, since their root-length growth and chlorophyll content were higher than the control, as well as their unchanged percentage survival. In contrast, copper treatments caused progressive reduction in the above mentioned parameters in copper-sensitive plants. The total uptake of copper and its distribution between roots and shoots differ significantly between the two populations. At all external copper concentrations the sensitive plants took up more copper, and a higher percentage of the total copper concentration was allocated to the shoot, compared with the tolerant plants. A distinct population differentiation was observed with respect to the distribution of calcium, magnesium, iron and potassium in roots and shoot-leaves. Under copper treatments the sensitive population showed a direct relation to the calcium concentration both in roots and shoot-leaves, while the tolerant population revealed an inverse relation to calcium concentration in plant tissues. The magnesium concentration decreased in the presence of increasing copper levels both in tolerant and, especially, sensitive populations. The total iron concentration seems to be unaffected under an excess of copper in tolerant plants, while an inverse relation of iron concentration to external copper supply in the sensitive population was observed. The concentration of potassium dropped more in sensitive plants. It seems likely that a constitutive copper tolerance mechanism also operates both in shoot and root and that this also contributes to the increased copper requirements of tolerant plants.