Nickel toxicity in two durum wheat cultivars differing in drought sensitivity

The effects of nickel (Ni) on growth, leaf water status, and mineral nutrient concentration were studied in two wheat (Triticum durum Desf.) cultivars with different sensitivity to water stress: 'Adamello' [drought sensitive (DS)] and 'Ofanto' [drought tolerant, (DT)]. The DT cultivar showed a higher Ni absorption capacity: 'Ofanto' seedlings grown in the presence of 35 mu M Ni had a 3.5 times greater concentration of Ni in roots than did 'Adamello'. Despite the greater Ni tissue content, the DT cultivar exhibited better growth and nutritional status when compared to the DS cultivar. In the DS cultivar the concentration of chlorophyll a and b was reduced by Ni treatment. Chlorophyll a concentration decreased in the DT cultivar, but to a lesser extent than in the DS cultivar; chlorophyll b was not altered by Ni level in the DT cultivar. Nickel caused a decrease in the water potential (psi(W)) and relative water content (RWC) in both cultivars, but these decreases were greater in the DS cultivar. The antioxidative defense enzymes, guaiacol peroxidase, ascorbate peroxidase, and glutathione reductase, showed increased activity in Ni-treated DS seedlings; this increase in activity was not observed in the DT seedlings. These data suggest that different wheat genotypes may markedly differ in Ni uptake and sensitivity and that a enhanced capacity to counteract Ni stress may be associated with drought resistance.