Changes in polyamine synthesis during anther development and pollen germination in tobacco (Nicotiana tabacum)

Changes in polyamine levels and in the activities of arginine decarboxylase (ADC, EC 4.1.1.19) and omithine decarboxylase (ODC. EC 4.1.1.17) were studied during anther development in Nicotiana tabacum as well as during the first 120 min of dry pollen germination in vitro. Arginine decarboxylase activity was more abundant than that of ODC in the whole anther and isolated pollen: activities of both enzymes reached a maximum at the binucleate stage of pollen development and increased with elongation of the pollen tube. During anther development, no alteration in free putrescine (Put) or in free spermidine (Spd) was found from the microspore to the binucleate stage. However, during maturation, free Put decreased, probably because of its transformation into Spd. Bound polyammes were more abundant than the free polyamines during anther development. The presence of a‐amanitin. on inhibitor of transcription, did not affect ADC activity during the germination process, whereas cycloheximide. on inhibitor of protein synthesis, had a strong inhibitory effect. Compared to their levels in dry pollen, free Put. Spd and spermine (Spm), and bound Put were present at increased levels during pollen tube elongation. However, in the presence of cycloheximide. which had little effect on elongation of the pollen tube, free polyamine synthesis was inhibited. In light of the results obtained with cycloheximide and difluoromethvlargi‐nine. An inhibitor of arginine decarboxylase. which inhibited elongation but not emergence of the pollen tube, we propose that the endogenous polyamine liter in dry pollen was sufficient to contribute to the emergence of the pollen tube and. once emergence was established, that pre‐existent ADC and ODC were responsible for the synthesis of those polyaraines related to tube elongation, since the polyamine levels of the dry pollen appeared to be insufficient.