POLYAMINE TRANSLOCATION FOLLOWING PHOTOPERIODIC FLOWERING INDUCTION IN SOYBEAN

Radioactivity translocation after [C-14]-spermidine application over t he third trifoliate leaf of soybean plants (Glycine max [L.] Merr, cv. Williams) was checked during the first 72 h of short day (SD) treatme nt to study the involvement of polyamines (PAs) in photoperiodic flowe ring induction. PAs and/or their metabolites were translocated from th e supplied leaf to all parts of the plant. Radioactivity reached its h ighest 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 concent ration. The first arose after the first inductive night, coinciding wi th the proper flowering induction process; the second one arose after the third inductive night, coinciding with the first morphological sym ptoms of the transition of vegetative meristems to the reproductive co ndition. Soluble free PAs showed a different balance in the apical bud of SD-induced plants compared with LD-non induced control plants. Sol uble conjugated PAs were detected as traces. It is suggested that unde r 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 firs t step, to the fact that they were part of the complex mechanism of th e flowering signal, and in a second step, to the flower transition of vegetative buds.