POLYAMINE SPARING MAY BE INVOLVED IN THE PROLONGATION OF CELL-DIVISION DUE TO INHIBITION OF PHENYLPROPANOID SYNTHESIS IN CYTOKININ-STARVED SOYBEAN CELLS

Effects on growth, mostly of an inhibitory nature, have been attribute d to phenolic compounds in vivo and in vitro. This suggests that L-alp ha-aminooxy-beta-phenylpropionic acid (L-AOPP), a competitive inhibito r of phenylalanine ammonia-lyase (PAL), the enzyme controlling the fir st step in phenylpropanoid synthesis, might stimulate growth in soybea n suspension cultures (Glycine max, cv. Acme), The promotive effect of L-AOPP, measured as an increase in cell number, was more clearly dete cted in the growth-limiting condition of cytokinin starvation. At leas t one more cell division cycle was completed in the presence of L-AOPP before growth by division ceased and growth continued by expansion on ly. Phenolic acids are known to conjugate with polyamines, modulating the free levels of these plant growth substances. Thus, the effect of L-AOPP on the titers of free and conjugated polyamines (putrescine, sp ermidine, and spermine) was investigated by high performance liquid ch romatography in the course of cytokinin starvation. An increased level of free putrescine was detected in the presence of L-AOPP relative to controls, especially in the initial period before growth became restr icted to cell expansion. The decrease in free putrescine associated wi th the cessation of cell division was temporarily delayed, suggesting that an interaction between phenolic acids and polyamines is involved in the mechanism of growth promotion by L-AOPP.