COMPARATIVE RESPONSES OF A COPPER-TOLERANT AND A COPPER-SENSITIVE POPULATION OF MINUARTIA-HIRSUTA TO COPPER TOXICITY

The response of two populations of Minuartia hirsuta with different co pper tolerance to an excess of copper was studied. The population orig inating from copper contaminated sites showed a distinct tolerance to copper. A more vigorous growth of copper tolerant plants under increas ing copper concentrations was found, since their root-length growth an d chlorophyll content were higher than the control, as well as their u nchanged percentage survival. In contrast, copper treatments caused pr ogressive reduction in the above mentioned parameters in copper-sensit ive plants. The total uptake of copper and its distribution between ro ots and shoots differ significantly between the two populations. At al l external copper concentrations the sensitive plants took up more cop per, and a higher percentage of the total copper concentration was all ocated to the shoot, compared with the tolerant plants. A distinct pop ulation differentiation was observed with respect to the distribution of calcium, magnesium, iron and potassium in roots and shoot-leaves. U nder copper treatments the sensitive population showed a direct relati on to the calcium concentration both in roots and shoot-leaves, while the tolerant population revealed an inverse relation to calcium concen tration 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 unaf fected under an excess of copper in tolerant plants, while an inverse relation of iron concentration to external copper supply in the sensit ive population was observed. The concentration of potassium dropped mo re in sensitive plants. It seems likely that a constitutive copper tol erance mechanism also operates both in shoot and root and that this al so contributes to the increased copper requirements of tolerant plants .