Ni2+ accumulation and the toxic effects of Ni2+ On growth were investigated in pea seedlings. In roots, Ni2+ absorption increased as a function of metal supply, while in the shoots the accumulation of the metal was restricted, particularly with higher treatments. Ten mu mol/L Ni2+ was found to be the lowest effective concentration to cause a significant reduction in root growth. Ni2+ did not induce changes in shoot length, even though biomass production was affected in both roots and shoots. The toxic effects of Ni2+ on K+ uptake and on water content were markedly higher in roots than in shoots. In the Ni-treated roots, these effects, and the concomitant increase in phenol content and extracellular peroxidase activity with affinity towards syringaldazine, were associated with an early induced cellular differentiation. The significance of this senescent-like slate, together with other cellular defence mechanisms such as the stimulation of intracellular peroxidase activity, is discussed in relation to Ni-stress.
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