Abstract: Present study have focused on the polyamine biosynthetic pathway as a model to unravel those key factors that still present bottlenecks in metabolic pathway engineering in plants. By engineering rice plants with the oat adc cDNA under the control of two different promoters we demonstrated a correlation between polyamine accumulation and the ability of dedifferentiated tissue to undergo morphogenesis. We suggested also that a key element in facilitating changes in polyamine levels in transgenic tissues is the strength of the promoter used to drive expression of particular transgenes. Based on these results we developed a model, which stipulates a minimum threshold in putrescine concentration prior to its further conversion into the higher polyamines spermidine and spermine. Present experiments also demonstrated that seed rather than vegetative tissue is the preferred organ for polyamine accumulation and storage. Present studies shed further light on the complexity of polyamine biosynthesis in intact plants and tissues and provide a basis for their further manipulation using additional genes of the polyamine pathway.