REQUIREMENT OF POLYAMINES FOR IN-VITRO MATURATION OF THE MID-BINUCLEATE POLLEN OF NICOTIANA-TABACUM

We have studied the changes in endogenous levels of both free and conjugated polyamines (PA) during <<in-vitro>> transition of pollen grains of Nicotiana tabacum from the mid-binucleate (MB) stage to matured MB (MBM) and matured germinated MB (MBG) stages. Spermidine (Spd) was the most abundant PA in all stages, followed by putrescine (Put) and spermine (Spm). An increase in all forms of PA was observed in the transition of MB to MBM; however, a decrease from MBM to MBG was obtained. The pollen matured <<in-vitro>> contains more PA than the one matured <<in-situ>> surrounded by sporophytic tissue. This increase may be due to the fact that glutamine (present in the maturation medium) is related to arginine and ornithine metabolism. The effect of PA biosynthesis inhibitors, DL-difluoromethylarginine (DFMA), DL-difluoromethylornithine (DFMO) or cyclohexylamine (CHA), on maturation and germination processes was also studied. The results suggested that PA biosynthesis <<via ornithine decarboxylase<< is required for <<in-vitro>> maturation. However, ornithine decarboxylase (ODC) and arginine decarboxylase (ADC) appeared to be implicated in <<in-vitro>> as well as <<in-situ>> germination processes. The inhibition induced by DFMO and DFMA was overcome by addition of Put. The content of all forms of PA was also quantified in MB pollen matured in the presence of PA inhibitors in order to support the importance of PA biosynthesis in the maturation process.