Contents of polyamines and 1-aminocyclopropane-1-carboxylic acid (ACC) in Hiproly barley callus were examined under different culture conditions. After auxin withdrawal, the contents of free polyamines changed conversely to the contents of ACC. In the absence of auxin, incorporation of L-[3, 4-¹⁴C]methionine into polyamines and the activity of S-adenosylmethionine decarboxylase (SAMDCase) in the callus increased, then remained stable, but incorporation of L-[3, 4-¹⁴C]methionine into ACC, precursor of ethylene and ACC synthase activity once declined and increased again.
Aminooxyacetic acid (AOA) affected the increase in the levels of polyamines in the callus. 1-Aminoisobutyric acid (AIB) had a slight effect on the polyamine production. The incorporation of L-[3, 4-¹⁴C]methionine into ACC and ACC synthase activity were inhibited by AOA, but not by AIB. AOA stimulated the activity of SAMDCase, and also enhanced the incorporation of L-[3, 4-¹⁴C]methionine into polyamines in the callus. Methylglyoxal-bis(guanylhydrazone) (MGBG) greatly enhanced the ACC production. The rate of incorporation of L-[3, 4-¹⁴C]methionine into ACC and ACC synthase activity in the callus were significantly enhanced by MGBG. MGBG strongly inhibited SAMDCase activity and the incorporation of L-[3, 4-¹⁴C]methionine into polyamines. Moreover, the synthesis of polyamines was inhibited by MGBG.
These results suggested that in Hiproly barley callus ACC production has an important effect on changes in the polyamine levels, and that polyamine and ethylene biosynthetic pathways are regulated by competition against each other.

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