Ethylene-enhanced Synthesis of Phenylalanine Ammonia-Lyase in Pea Seedlings

The effect of ethylene on the development of phenylalanine ammonia-lyase activity in segments excised from the epicotyl apex of pea seedling was studied. Although there was some increase in phenylalanine ammonia-lyase activity in segments not treated with ethylene, a marked increase in phenylalanine ammonia-lyase activity occurred in ethylene-treated tissues during the incubation. The induction period was estimated to be about 6 hours. The activity reached a maxmum at 30 hours and then declined. On withdrawal of ethylene, the increase was sustained for a short period and then stopped. After retreatment with ethylene, the increase was resumed. Addition of CO(2) reduced the effect of ethylene. Administration of cycloheximide or actinomycin D at an early period almost completely suppressed the increase in phenylalanine ammonia-lyase activity. However, if these inhibitors were administered at a later period, while phenylalanine ammonia-lyase activity was approaching a maximum, they not only failed to reduce but rather stimulated the activity. These results are consistent with the view that there exist both phenylalanine ammonia-lyase-synthesizing and -inactivating systems, and that the development of both systems may involve de novo synthesis of protein.