EARLY CHANGES IN THE CONTENT OF LEAF POLYAMINES DURING THE PHOTOPERIODIC FLOWERING INDUCTION IN SOYBEAN

Changes in the endogenous polyamine (PA) fractions, i.e. free PA, acid -soluble bound PA and acid-insoluble bound PA, were analysed in leaves of soybean plants during the first days of short day (SD) flowering i nduction. Free putrescine, spermidine and spermine titers decreased at the end of the first inductive 15 h-long night (flowering induction) and only the free putrescine titer decreased at the end of the third i nductive long night (meristematic transition to the reproductive stage ). These results are consistent with previous observations of the exis tence of two peaks in PA translocation from leaves as well as with sim ultaneous changes in their content in the apical bud at these same two moments, suggesting that there is a close relationship between the le af (source) and the apical bud (sink) during the photoperiodic inducti on of flowering and meristem evocation and transition.