An enzyme activity, found for the first time in plants, mainly located in the 22,000g supernatant of the crude extract of sprout apices of Helianthus tuberosus L. cv OB1 tubers, is able in vitro to covalently bind polyamines to endogenous substrates of different molecular weights. The major assay parameters, such as pH, dithiothreitol, and extract concentrations were optimized. The time course of the reaction, the dependence on putrescine concentration, its competition with histamine, the capacity to bind spermidine and spermine better than putrescine, the stability of the reaction product and analysis of the latter by sodium dodecyl sulfate polyacrylamide gel electrophoresis and thin-layer chromatography suggest that putrescine is linked to endogenous substrates by means of an enzyme reaction that shows some similarities with transglutaminase activities detected in animals. However, the activities of the crude extract and of a fraction eluted from a Sephadex G25 column were not affected by CaCI2 concentrations lower or equal to 5 millimolar, 4 or 10 millimolar EGTA caused a very small reduction; higher concentrations of CaCI2 and 15 millimolar or more of EDTA were inhibitory. N,N'-dimethylcasein was not recognized as a substrate. These data indicate that this activity also displays some characteristics which are different from those of animal transglutaminases.

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N. 1986. Ornithine and arginine decarboxylases and polyamine involvement during in vivo differentiation and in vitro dedifferentiation of Datura innoxia leaf explants. -Physjol. Plantarum 68: 589-596.The effects of exogenous ornithine, arginine and poiyamines added to media leading to root, callus or bud initiation of Datura innoxia Mill, leaf explants growing in vitro were examined. Omithine and arginine decarboxylase activities (ODC, EC 4.1.1. !7; ADC, EC 4.1.1.19) as well as endogenous polyamine levels were also determined during the course of in vivo differentiation of the leaves and their subsequent in vitro dedifferentiation utider rooting, callusing, or budding conditions. Decarboxylase activities were determined by measuring the '*CO, released and the polyamines were quantified after dansylation by thin-layer chromatography. In vivo, ODC and ADC activities decreased from shoots to young to old leaves, in vitro, synergistic effects between omithine and indole-3-acetic acid on rhizogenesis were detected, while arginine was not effective. Exogenous putrescine also acted synergistically with auxin by promoting root growth. A close relationship was found between rhizogenesis, OC>C activity and increase in endogenous putrescine and spermidine levels. ODC increased during the induction and time course of cell dedifferentiation and seemed to support these events, while ADC seemed to support only the later events involving redifferentiation.

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