RESUMO
Root Surface acid phosphatase activity was assessed in seedlings of two species of Alyssum, one endemic to Tuscan serpentines (Alyssum bertolonii Desv.) and the other of wide occurrence (Alyssum saxatile L.), cultivated in solutions to which various concentrations of Ni2+ , Ca2+ and Mg2+ were added. Treatments were applied in two factorial experiments of type 2n . A concentration of 0.01 mM Ni2+ markedly stimulated phosphatase activity in A. bertolonii, but slightly decreased it in A. saxatile. Increased Ca2+ concentration stimulated enzyme activity in both species, hut in A. bertolonii the highest activity was obtained with low Ca2+ concentrations, whilst the opposite occured in A. saxatile. A. bertolonii instead required high Mg2+ concentrations to increase phosphatase activity significantly. The same concentrations were toxic to A. saxatile. In the serpentine species, favourable conditions for the increase of phosphatase activity were induced by a high Mg2+ /Ca2+ ratio, which also favoured dry mass production. Therefore it is possible that the increase of phosphatase activity might be an aspect of plant adaptation to serpentines.