RELATIONSHIPS AMONG PHENYLALANINE AMMONIA-LYASE ACTIVITY, SIMPLE PHENOL CONCENTRATIONS AND ANTHOCYANIN ACCUMULATION IN APPLE

Three years of experiments with both fruit and fruit skin disks of app le (Malus domestica Borkh. cultivar 'Delicious') were carried out to s tudy the relationships among phenylalanine ammonia-lyase (PAL, E.C.4.3 .1.5) activity, simple phenol concentrations and anthocyanin accumulat ion. PAL activity increased greatly during 30 days after full bloom (D AFB), decreased rapidly until 60 DAFB, and then remained relatively co nstant during fruit enlargement and fruit coloring. Simple phenol cont ent generally correlated with changes of PAL activity except at 30-60 DAFB. There were two peaks of anthocyanin accumulation, one at the fru itlet stage and another at the fruit maturation stage. The first peak paralleled changes in PAL activity, but the second did not. L-alpha-am inooxy-beta-phenylpropionic acid (L-AOPP) inhibited PAL activity in ma ture fruit and in mature skin disks by approximately 45% and 80%, and reduced simple phenol content by about 36% and 78%, respectively, but did not change anthocyanin content significantly. Fruit bagging signif icantly inhibited both PAL activity and anthocyanin synthesis, while b ag removal enhanced both of them. Application of L-AOPP to fruit immed iately after bag removal inhibited PAL activity and reduced both simpl e phenol and anthocyanin accumulations. We conclude that while PAL cat alyzes a reaction to produce precursors of anthocyanin synthesis, unde r conditions of sufficient precursors, changes in anthocyanin accumula tion can occur independently of changes in PAL activity.