Polyamine translocation following photoperiodic flowering induction in soybean

Radioactivity translocation after [¹⁴C]-spermidine application over the third trifoliate leaf of soybean plants ( Glycine max . [L.] Merr, cv. Williams) was checked during the first 72 h of short day (SD) treatment to study the involvement of polyamines (PAs) in photoperiodic flowering induction. PAs and/or their metabolites were translocated from the supplied leaf to all parts of the plant. Radioactivity reached its highest concentration in the upper portion of the stem, i.e. the apical bud and the youngest leaf. After the beginning of the first inductive night, the detected radioactivity showed two peaks of maximal concentration. The first arose after the first inductive night, coinciding with the proper flowering induction process; the second one arose after the third inductive night, coinciding with the first morphological symptoms of the transition of vegetative meristems to the reproductive condition. Soluble free PAs showed a different balance in the apical bud of SD-induced plants compared with LD-non induced control plants. Soluble conjugated PAs were detected as traces. It is suggested that under flowering inductive conditions, PAs play a different role according to the stage of the flowering process. Thus, their translocation from the leaves to the axillary and apical buds might be related, in a first step, to the fact that they were part of the complex mechanism of the flowering signal, and in a second step, to the flower transition of vegetative buds.