A SURVEY OF WOUND-INDUCED AND METHYL JASMONATE-INDUCED LEAF POLYPHENOL OXIDASE IN CROP PLANTS

Polyphenol oxidases (PPOs) are widespread enzymes which oxidize plant phenolic compounds. In tomato leaves, PPO is systemically wound-induce d, regulated by the tomato wound signal systemin via the octadecanoid wound-signalling pathway, and appears to function as an anti-nutritive defense against folivore insect pests. In order to determine if PPO c ould be important for the induced defense of other crop plants, plants from five plant families were surveyed for constitutive, wound-induce d, and methyl jasmonate-induced PPO activity. In addition to tomato, P PO was most strongly induced by wounding or methyl jasmonate in tobacc o and hybrid poplar. In these plants the response was also shown to be systemically induced by wounding. Two species, willow and soybean, ha d very high constitutive PPO activities yet showed no significant PPO induction. Most of the species tested had low constitutive levels of P PO activity, and low or no induction by wounding or methyl jasmonate. Although PPO is widely distributed, only in some species does it appea r to be a component of the inducible anti-herbivore defense. (C) 1997 Elsevier Science Ltd. All rights reserved.