Growth, peroxidase activity and cytological modifications in Pisum sativumseedlings exposed to Ni2+ toxicity

Ni2+ accumulation and the toxic effects of Ni2+ On growth were investigated in pea seedlings. In roots, Ni2+ absorption increased as a function of met al 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 th e lowest effective concentration to cause a significant reduction in root g rowth. Ni2+ did not induce changes in shoot length, even though biomass pro duction 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 shoot s. 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 differentiat ion. The significance of this senescent-like slate, together with other cel lular defence mechanisms such as the stimulation of intracellular peroxidas e activity, is discussed in relation to Ni-stress.