l-Phenylalanine Ammonia-Lyase Activity During Germination of Phaseolus vulgaris

Abstract

l-Phenylalanine ammonia-lyase (PAL) activity develops in excised bean axes after approximately 5 hours of incubation and reaches a maximum level after 14 hours of incubation. Light does not affect the development of activity, but puromycin, cycloheximide, actinomycin D, and 5-fluorouracil inhibit.During this period of incubation both d- and l-p-fluorophenylalanine stimulate fresh weight increase and both inhibit the development of PAL activity. Neither l- nor d-phenylalanine stimulates fresh weight increase while the former inhibits development of PAL activity and the latter has no effect. Neither d isomer is deaminated while l-p-fluorophenylalanine is deaminated at about one-half the rate of l-phenylalanine. It is suggested that fluorophenylalanine does not stimulate the fresh weight increase by its effects on the phenolics pathway.Trans-cinnamic acid was found to inhibit both the development of PAL activity and the in vitro deamination of l-phenylalanine. Various hydroxycinnamic acids, although inhibiting the development of PAL activity, had little or no effect on the in vitro deamination of l-phenylalanine.No tyrosine ammonia-lyase activity was found in the axes and l-tyrosine had no effect on the in vitro deamination of l-phenylalanine.The pattern of PAL development in intact seedlings differs markedly from that which occurs in the excised axes, although light also has no effect on the course of activity.