Polyphenoloxidase and the Respiration of Ivy Leaves

1. Polyphenoloxidase is present in ivy leaves but not in thoseof Aucuba or Euonymus.
2. Respiration of intact ivy leaves wasmarkedly stimulated bycatechol (R.Q. approximately=I), gallicacid, caffeic acid,and dihydroxyphenylalanine. The stimulationwas not relatedto injury as far as could be detected and wasnot followed byinhibition. The extra oxygen consumption representsa many timesrepeated oxidation of the amount of catechol supplied.
3. The effect of catechol on the respiration of Aucuba and Euonymusleaves was very small.
4. Cupferron and phenylthiourea, whichinhibit polyphenoloxidasein vitro, nevertheless increased respirationwhen administeredto leaves through the petiole. On the otherhand, when appliedby infiltration, cupferron did cause inhibition,but in Aucubaand Euonymus as much as in ivy.