Polyamines in Cultured Artichoke Explants: Effects are Primarily on Xylogenesis Rather than Cell Division

Phillips, R., Press, M. C., Bingham, L. and Grimmer, C. 1988. Polyamines in cultured artichoke expiants: effects are primarily on xylogenesis rather than cell division.—J. exp. Bot. 39: 473-480. The relationship between cell division and xylogenesis and polyamine metabolism was investigated in short-term cultures of Helianthus tuberosus tuber expiants via studies on inhibitors of polyamine biosynthesis, exogenous supply of spermidine and comparisons between proliferating and non proliferating treatments. Difluoromethylarginine (DFMA) and difluoromethylornithine (DFMO) did not substantially affect cell division rates but were inhibitory to xylem differentiation, especially higher concentrations of DFMO, which also stimulated endogenous spermidine accumulation. Exogenously supplied spermidine inhibited xylogenesis much more than cell division at concentra tions of 10 mol m~3 and above after 3 d culture. A possible inverse correlation between spermidine accumulation and cytodifferentiation is discussed. No significant differences in polyamines were found between proliferating cultures and those in which DNA replication and mitosis were blocked by gamma-irradiation, except for the late appearance of putrescine in irradiated cultures, possibly asa senescence response. Key words—Polyamines, DFMA, DFMO, Helianthus tuberosas, cultured expiants, cell division, xylem differentiation. Correspondence to: Department of Botany and Microbiology, University College London, Gower Street, London WC1E 6BT, U.K.