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In the short-day plant Chrysanthemum (Chrysanthemum morifolium Ramat. variety Pavo) putrescine and spermidine conjugates appeared in the apical bud before the first observable transformation of the meristem into floral structures . These compounds accumulated on floral initiation and well before floral evocation . Spermidine conjugates were predominant during floral initiation whereas free amines did not accumulate to any significant extent . Different associations of amides were observed during floral initiation as compared with the reproductive phase . 3,4-Dimethoxyphenethylamine conjugates (water-insoluble compounds) were the predominant amine conjugates observed during flower development . These compounds decreased drastically after fertilization . In vegetative buds from plants grown in long days polyamine conjugates were very low and appeared as plants aged . We present evidence that omithine decarboxylase (ODC) regulates putrescine biosynthesis during floral initiation and floral development . When ODC action was blocked by DFMO (a-DL-difluoromethylornithine, a specific, irreversible inhibitor of ODC), flowering was inhibited, and free and conjugated polyamines were not detected . This treatment led to a slight enhancement of ADC activity . When putrescine was added, polyamine titers and flowering were restored . A similar treatment with DFMA (a-DL difluoromethylarginine, a specific, irreversible inhibitor of ADC) did not affect flowering and the polyamine titers . The results suggest that ODC and polyamine conjugates are involved in regulating floral initiation in Chrysanthemum .Abbreviations : ADC = arginine decarboxylase ; ODC = ornithine decarboxylase ; DFMA = a-DLdifluoromethylarginine ; DFMO = a-DL-difluoromethylomithine .

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In Chrysanthemum leaf explants cultivated in vitro the capacity to covalently link polyamines to protein substances exists. This plant enzyme activity shows some similarities with mammalian transglutaminases. In foliar explants cultured on a medium promoting bud or root formation increasing levels of transglutaminase-like activity occurred during the first days of culture when cell multiplication was rapid then the levels declined as the rate of cell division decreased and differentiation occurred. Undifferentiated callus exhibited low transglutaminase-like activity. Transglutaminase-like activity also increased in rapidly proliferating and growing organs (roots and buds initiated from the foliar explants) and decreased during maturity. The relationship among transglutaminases-like activity, cell division, bud and root formation is discussed.Abbreviations: TGase = transglutaminase; BA = benzyladenine; 2,4-D = 2,4-dichlorophenoxyacetic acid; Put = putrescine; Spd = spermidine.-