L-Phenylalanine ammonia-lyase activity in asparagus spears : Effects of excision and incubation

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Incubation of disks sectioned from the basal portion of asparagus spears resulted in a 5-fold increase in L-phenylalanine ammonia-lyase (PAL) (E.C. 4.3.1.5) activity over the level initially present in the intact tissue. The enhanced activity developed rapidly, with only a slight lag, increasing to a maximum level at 30 hr. Thereafter, the level of activity decreased to 50% of maximum activity and appeared to have attained a new, higher steady-state level after 72 hr of incubation. Similar levels of activity developed in basal disks incubated either in buffer solution or in air, and light had no effect on enzyme activity. The excision-promoted increase in enzyme activity was prevented by cycloheximide (20 ppm) but, unlike some other tissues, delayed addition of the antibiotic to incubating disks promoted loss of the lyase activity. The phenylpropanoid end products, transcinnamate, p-coumarate and ferulate (at 10^<-3> M each) , in decreasing order of effectiveness, also inhibited the excision-promoted increase in enzyme activity and caused a loss of the enhanced activity in the incubated disks. The possibility is discussed that the activity initially present in the spears is under separate control from that activity induced by excision.
日本植物生理学会の論文