Effect of various inhibitors of polyamine synthesis on the growth of Helianthus tuberosus.

The growth effect of various inhibitors of polyamine synthesis was studied on explants obtained from Helianthus tuberosus tubers during dormancy and dormancy break and cultured for 20 days on a sterile agarized medium. Explant growth was strongly inhibited by canavanine and canaline, natural non-protein amino acid analogues of arginine and ornithine, respectively, as well as by canavanine in combination with putrescine. Methylglyoxal-bis-guanylhydrazone, an inhibitor of S-adenosylmethionine decarboxylase, did not increase growth inhibition caused by canavanine. Methylglyoxal-bis-guanylhydrazone alone, as well as alpha-methylornithine, 1,3-diaminopropane and 1,3-diaminopropan-2-o1 - which are inhibitors of ornithine decarboxylase - showed no growth inhibition with respect to the control treated with 2,4-dichlorophenoxyacetic acid. 1,3-Diaminopropane caused a paradoxic enhancement of callus growth and a much greater polyamine accumulation than in the control with 2,4-dichlorophenoxyacetic acid alone. During the first cell cycle inactivated tuber slices, 40 microM methylglyoxal-bis-guanylhydrazone inhibited spermidine and spermine synthesis up to 6 h, and their accumulation up to 1 h; RNA synthesis and accumulation and DNA accumulation were reduced at 1 h, and later enhanced. During the same period, 1 mM canavanine inhibited putrescine synthesis in the S and M phases, and spermidine and spermine synthesis only at 24 h; accumulation of putrescine and spermidine was reduced only at 12 h. Canavanine also reduced RNA synthesis throughout the S and M phases, while RNA accumulation was reduced at 18 and 24 h. Two different hypotheses are put forward concerning the induction of new pathways of polyamine synthesis.