NICKEL TOXICITY AND PEROXIDASE-ACTIVITY IN SEEDLINGS OF TRITICUM-AESTIVUM L

Ni2+ toxicity was evaluated in Triticum aestivum L. by its effects on root and shoot length, dry matter Production and water content. Over a threshold value of 20 mmol m-3 Ni2+ the degree of toxicity increases as a function of the Ni2+ concentration in the medium. Ni2+-treated roots show enhanced lipid peroxidation; the higher Ni2+ treatment (40 mmol m-3) also increases leakage of K+. In roots and shoots, Ni2+ enhances both guaiacol and syringaldazine extracellular peroxidase activity. The increase in extracellular peroxidase activity is also associated with an increase in the phenolic contents of roots and shoots. The observed growth inhibition might be partly the result of the effect of Ni2+ on cell turgor and cell-wall extensibility. Intracellular soluble peroxidases are also stimulated by Ni2+; such effects, independently of the substrate, were detected in extracts of Ni2+-treated shoots at a lower Ni2+ concentration than in the roots. Intracellular peroxidases might act as scavengers of peroxide radicals produced as a result of nickel toxicity.