Of the four 2iP derivatives applied to cut carnations 2iP, IPA and IPAMP delayed the rate of flower senescence but did not delay longevity . 2iP9G was the least effective . ['H]2iP was rapidly transported to all flower components . The receptacular tissue apparently plays a major role in the distribution of the applied cytokinin to the rest of the flower parts . Over and above possible interconversion between 2iP, IPA and IPAMP the applied [' H]2iP was also converted to 2iP9G, Ade, Ado, tZ and DHZ . The presence of Ade indicates the involvement of cytokinin oxidase-type enzymes while the presence of tZ and DHZ indicates a degree of hydroxylation . These latter steps may contribute to the efficiency of 2iP in the system .

The effect of inhibitors of polyamine biosynthesis on the development of embryogenic cell cultures of celery (Apium graveolus L.) was studied. Several developmental stages of somatic embryos were compared for differences in the content and biosynthesis of free polyamines and for cytokinin content. Cyclohexylamine and particularly methylglyoxal bis(guanylhydrazone), inhibited both cell division and the organization of polar embryos from globular embryos. Difluoromethylornithine slightly promoted embryo development, especially cell division.The free putrescine content of globular embryos was 6-fold that of fully differentiated plantlets, and that of spermidine 2-fold. Only a slight increase in the spermine content was found with embryo development. These differences were confirmed by data from polyamine biosynthesis. Incorporation of 14C-arginine into polyamines was slightly higher than that of 14C-ornithine. Over 96% of this incorporation was detected in the putrescine fraction. Incorporation of 14C into putrescine in globular embryos was 3 to 4-fold that in fully-differentiated plantlets. Incorporation into spermidine and spermine was, however, higher in plantlets than in globular embryos.Cytokinin analysis revealed considerable differences in the biological activity between the developmental stages of embryogenesis. This could be due to endogenous cytokinins and/or BA taken up from the maintenance medium. Cytokinin levels decreased with increased embryo development. Most of the detected cytokinin-like activity co-chromatographed with BA and its metabolites. Some as yet unidentified peaks of activity were recorded in the globular embryos.The results are considered with respect to the possible participation of polyamines and cytokinins in the development of embryogenic cell cultures of celery. It is suggested that the onset of embryogenesis is characterized by a high content of putrescine and cytokinins, while a decrease in putrescine synthesis and cytokinin content, and an increase in spermidine and spermine content, accompany further embryo development and plantlet formation.Abbreviations: ADC = arginine decarboxylase; ODC = ornithine decarboxylase; 2,4-D = dichlorophenoxyacetic acid; DFMA = difluoromethylarginine; DFMO = difluoromethylornithine; MGBG = methylglyoxal bis(guanylhydrazone); CHA = cyclohexylamine; BA = benzyladenine; BAR = benzyladenine riboside 246

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The polyamines putrescine and spermine were effective in delaying the senescence of carnation buds, but were ineffective when applied to flowers of which the petals had already opened, and were 90°with respect to the stem . Higher levels of endogenous putrescine were detected in the open flowers than in the buds, and this may explain the negative effect obtained when polyamines were applied to open flowers that were picked for commercial distribution .Abbreviations . AOA = amino-oxyacetic acid ; AVG = amino-ethoxyvinyl-glycine ; SAM = S-adenosyl methionine ; STS = silver thiosulphate .