title: Polyphenol oxidase as a biochemical seed defense mechanism.
abstract: Seed dormancy and resistance to decay are fundamental survival strategies, which allow a population of seeds to germinate over long periods of time. Seeds have physical, chemical, and biological defense mechanisms that protect their food reserves from decay-inducing organisms and herbivores. Here, we hypothesize that seeds also possess enzyme-based biochemical defenses, based on induction of the plant defense enzyme, polyphenol oxidase (PPO), when wild oat (Avena fatua L.) caryopses and seeds were challenged with seed-decaying Fusarium fungi. These studies suggest that dormant seeds are capable of mounting a defense response to pathogens. The pathogen-induced PPO activity from wild oat was attributed to a soluble isoform of the enzyme that appeared to result, at least in part, from proteolytic activation of a latent PPO isoform. PPO activity was also induced in wild oat hulls (lemma and palea), non-living tissues that cover and protect the caryopsis. These results are consistent with the hypothesis that seeds possess inducible enzyme-based biochemical defenses arrayed on the exterior of seeds and these defenses represent a fundamental mechanism of seed survival and longevity in the soil. Enzyme-based biochemical defenses may have broader implications since they may apply to other defense enzymes as well as to a diversity of plant species and ecosystems.
authors.affiliation: Department of Crop and Soil Sciences, Washington State University Pullman, WA, USA.
authors.forename: E Patrick
authors.initials: EP
authors.lastname: Fuerst
authors.affiliation: Root Disease and Biological Control Research Unit, United States Department of Agriculture - Agricultural Research Service, Washington State University Pullman, WA, USA.
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Okubara
authors.affiliation: Biosciences Research Laboratory, United States Department of Agriculture - Agricultural Research Service Fargo, ND, USA.
authors.forename: James V
authors.initials: JV
authors.lastname: Anderson
authors.affiliation: Western Wheat Quality Laboratory, United States Department of Agriculture - Agricultural Research Service, Washington State University Pullman, WA, USA.
authors.forename: Craig F
authors.initials: CF
authors.lastname: Morris
keywords: seed decay; seed defense; seed longevity; weed seed bank