The effect of AOA on ethylene and polyamine metabolism during early phasesof somatic embryogenesis in Medicago sativa

Changes in the levels of ethylene, 1-aminocyclopropane-1-carboxylic acid (A CC), 1-(malonylamino)cyclopropane-1-carboxylic acid (MACC) and polyamines w ere simultaneously investigated during the early phases of alfalfa somatic embryogenesis. These included the period of induction and subculture of cal lus, and 3- and 7-day suspension cultures for the induction of somatic embr yogenesis. The polyamines contained in the embryogenic callus were found to include putrescine (Put), spermidine (Spd) and spermine (Spm), but the lev el of Spm was much less than that of Put and Spd. There was a dramatic incr ease in MACC after induction of embryogenesis, and ACC levels were lower in somatic embryos than in embryogenic callus. Induction of embryogenesis for 3 days increased the levels of ACC and polyamines to a maximum level, and these then reduced as the embryogenesis proceeded. The ratios of Put/Spd an d ACC/MACC were decreased during the induction. This indicated that both hi gh levels of ACC and polyamines might be a prerequisite for early different iation during the induction of the embryogenesis. Thus, there appears not t o be competition between polyamine biosynthesis and ethylene biosynthesis a t least during the induction of somatic embryogenesis, because both the pol yamines and ACC were simultaneously increased during the induction period. Conversion of ACC into MACC and the maintenance of a relatively high level of polyamines, especially Spd, appear to be important for further developme nt of the embryos. When aminooxylvinylglycine (AOA) was added at the initiation of the callus subculture, it had no significant effect on the callus growth, the ethylene production and ACC level of the callus. However, AOA increased the numbers of the embryos accompanying an increase in Spd level and S-adenosylmethion ine decarboxylase (SAMDC) activity. Thus, the AOA effect could be associate d with Spd increase rather than with the effect of ethylene biosynthesis.