POLYAMINE METABOLISM AND GENE-REGULATION DURING THE TRANSITION OF AUTONOMOUS SUGAR-BEET CELLS IN SUSPENSION-CULTURE FROM QUIESCENCE TO DIVISION

Sugar beet cells grown in batch suspension culture have been used to s tudy the regulation of polyamine levels during the transition from a q uiescent to a proliferating state. The quiescent state was achieved by maintenance of the phytohormone autonomous cells in the stationary ph ase of the batch culture cycle. After subculture into fresh medium the re was an increase in DNA synthesis which was accompanied by a dramati c increase in cellular polyamine levels. The levels of both free and b ound cellular putrescine and spermidine within the cells reached a pea k before the onset of the first synchronous division. The levels of pu trescine, spermidine and to some extent spermine in the culture medium also increased dramatically shortly after subculture. The increase in polyamines was preceded by a rapid but transient increase in ornithin e decarboxylase (EC 4.1.1.17) and S-adenosylnethionine decarboxylase ( EC 4.1.1.50). Arginine decarboxylase (EC 4.1.1.19) and S-adenosylmethi onine synthetase (EC 2.5.1.6) activity did not show the same pattern o f cell division-related variation. Inhibition of S-adenosylmethionine biosynthesis with methylglyoxal bis-(guanylhydrazone) (MGBG) reduced c ell division in the suspension culture. Inhibitors of ornithine decarb oxylase and arginine decarboxylase individually had little effect on c ell division, but in combination led to a reduction in cell division. Addition of polyamines and their precursors to cells in the stationary phase of a batch culture cycle led to the induction of expression of a mitotic cyclin sequence (BvcycII).