INFLUENCE OF PRETREATMENTS WITH INHIBITORS OF PUTRESCINE SYNTHESIS ONPOLYAMINE METABOLISM AND DIFFERENTIATION PROCESSES OF MAIZE CALLUSES

The effect of short treatments with 10 mM DL-alpha-difluoromethylornit hine (DFMO) and DL-alpha-difluoromethylarginine (DFMA), irreversible i nhibitors of putrescine synthesis on growth, plant regeneration and en dogenous polyamine content of maize (Zea mays L.) callus cultures was investigated. The effect of exogenous putrescine and the enzymatic act ivities of arginine decarboxylase (ADC) and ornithine decarboxylase (O DC) were also studied. Of all the assayed treatments, only DFMA signif icantly decreased callus growth versus control. Enzymatic activity was markedly decreased by the addition of the respective inhibitors in al l the treatments. Furthermore, a decrease in ODC and ADC activities R as observed when DFMA and DFMO were added respectively to the medium. Whereas a predominance of ODC activity was detected in maintenance med ium, ADC activity was the prevalent in differentiation medium. Moreove r, DFMO pretreated calluses led to a marked increase in the number of buds with respect to all the other treatments and maintained the capac ity of the calluses to regenerate plants. By contrast, although DFMA p retreated calluses raised the number of regenerated plants versus cont rol, the number of buds were decreased and the calluses tended to be e liminated at the end of the differentiation period. The combined addit ion of putrescine and inhibitors reduced the regeneration rate and the enzymatic activities of the calluses. Nevertheless, the addition of p utrescine to the control medium increased the regeneration rate and th e number of plants. Differences in endogenous polyamine content (espec ially putrescine), depending on the treatments, were also observed.