Changes in phenylalanine ammonia-lyase levels in excised potato tuber tissue: effects of the gaseous environment and desensitization to cinnamate repression by in situ pre-incubation

The rise in phenylalanine ammonia-lyase (PAL) activity following excision of potato tuber discs is antagonized by increasing partial pressures of CO2 This inhibition is potentiated by depleting the atmospheric ethylene level. We suggest that the previously observed suppression of PAL appearance by in situ incubation of excised discs in reassembled tubers may be related to an internal atmosphere relatively rich in CO2 and of low ethylene content. The transition to an oscillatory time course of PAL activity that follows transfer of discs from in situ incubation to air appears to be accompanied by the development of enzyme activity becoming desensitized to repression by exogenous cinnamate. The concentration dependence of cinnamate uptake is not significantly altered by in situ pre-incubation of tuber discs.