Superinduction of cytosolic and chromatin-bound ornithine decarboxylase activities of germinating barley seeds by actinomycin D

Putrescine in plant cells is formed either from Larginine by L-arginine decarboxylase (EC 4.11.19, ADC) or directly from L-ornithine by L-ornithine decarboxylase (EC 4.11.17, ODC) [1-5]. The contribution of ODC to the formation of polyamines in plants was claimed to be insignificant, since ODC activity in most plant tissues was found to be much lower than that of ADC [6]. The only welldocumented work on ODC activity in plant cells is that in [4] on rapidly proliferating plant cells. Investigations to now on plant ODC were performed in the 10000 × g supernatant of plant tissue homogenates based on the assumption that ODC is a cytosolic enzyme. Here, evidence is presented that in barley seeds germinated for > 90 h, ODC activity is located mainly in the nucleus, tightly bound to chromatin, although the cytosol also possesses considerable activity. Both activities are superinduced when seed germination takes place in the presence of gibberellic acid and actinomycin D.