POLYAMINES IN THE INDUCTION OF NICOTIANA-TABACUM POLLEN EMBRYOGENESIS BY STARVATION

An increase in both putrescine (Put) and spermidine (Spd) bound to macromolecules was observed during ''in vitro'' embryogenic induction from isolated mid-binucleate (MB) pollen of Nicotiana tabacum. Free polyamines and Spd bound to small substances decreased in this period. We noticed in the fully formed embryos from embryogenic pollen (EP): (1) an increase in free Put and both Put and spermine (Spm) bound to small substances; (2) a decrease in both free Spd and Spm, and in Spd bound to small substances; and (3) a noticeable decrease of polyamines (PA) bound to macromolecules. During the process of embryogenesis, a gradual disappearance of ornithine decarboxylase (ODC) activity was observed. However, arginine decarboxylase (ADC) activity decreased along the induction period, increasing again during the embryo formation. Experiments with the inhibitors of polyamine synthesis difluoromethylornithine (DFMO) and difluoromethylarginine (DFMA) confirmed that PA biosynthesis is required for the embryo formation, but not for embryogenic induction.