Ni2+ and Cd2+ toxicity and effects on the activity of glucose-6-phosphate dehydrogenase (G6PDH, EC 1.1.1.49), glutamate dehydrogenase (GDH, EC 1.4.1.2), malic enzyme (ME, EC 1.1.1.40), and isocitrate dehydrogenase (ICDH, EC 1.1.1.42) were evaluated in two populations of Silene italica, a Ni-tolerant ecotype from serpentine soils very low in Cd2+, and a population sensitive to both Ni2+ and Cd2+ and originating from a normal soil. The Ni-tolerant population is more tolerant to both metals than the ecotype originating from a normal soil. Both Ni2+ and Cd2+ assimilation induce a stronger increase of G6PDH, GDH, and ICDH activity in the Ni-tolerant than in the Ni-sensitive population. In the Ni-tolerant population Cd2+ stimulates the activity of ME, GDH, and G6PDH to a greater extent than Ni2+ does. Our results suggest that the tolerant population reacts better than the sensitive one to the toxic metal concentrations; the effects on the enzyme activities described may be involved in the response to metal stress conditions.
