Polyamine Levels in Relation to Growth and Somatic Embryogenesis in Tissue 6Medicago SativaL.

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Abstract
Polyamine levels in petiole-derived tissue cultures of two highly regenerable Medicago sativa L. genotypes were determined during the embryo induction and embryo differentiation phases of somatic embryogenesis. Putrescine levels increased 27–32-fold during the 10 d on 2, 4-D- and kinetin-containing embryo induction medium and fell sharply following transfer to growth substance-free embryo differentiation medium. The rapid increase in putrescine content occurred during a period of relatively little growth while the decline coincided with the initiation of rapid tissue growth on embryo differentiation medium. The addition of putative inhibitors of putrescine or spermidine biosynthesis to the embryo induction medium led to reduced levels of polyamines, particularly of putrescine, in cultures of both genotypes but subsequent somatic embryo formation was inhibited in cultures of one genotype only. It was concluded that the pronounced change in putrescine metabolism was not specifically associated with embryogenesis, but appeared to be related generally to re-programming of cells into a new pattern of in vitro development.