Induction of Polyphenol Oxidase Activity in Dormant Wild Oat (Avena fatua) Seeds and Caryopses: A Defense Response to Seed Decay Fungi

• Published in: Weed science Vol. 59; no. 2; pp. 137 - 144
• Main Authors: Fuerst, E. Patrick, Anderson, James V, Kennedy, Ann C, Gallagher, Robert S
• Format: Journal Article
• Language: English
• Published: 810 East 10th Street, Lawrence, KS 66044-8897 Weed Science Society of America 01.04.2011; Cambridge University Press
• Subjects: Avena fatua; Biochemistry; Biological and medical sciences; buried seeds; catechol oxidase; decay fungi; deterioration resistance; dormancy; F. culmorum; fruits; Fundamental and applied biological sciences. Psychology; Fungal plant pathogens; Fungi; Fusarium avenaceum; hulls; leachates; molecular weight; Mycelium; Oats; Oxidases; Palea; Parasitic plants. Weeds; Pathogens; PHYSIOLOGY, CHEMISTRY, AND BIOCHEMISTRY; Phytopathology. Animal pests. Plant and forest protection; Plants; polyphenol oxidase; Polyphenols; Proteins; proteolysis; Pythium; Pythium ultimum; seed decay resistance; seed longevity; Seeds; Weeds; Western blotting; Fusarium avenaceum; F. culmorum; Pythium ultimum; deterioration resistance; seed decay resistance; seed longevity; polyphenol oxidase; Wild oat, Avena fatua L. AVEFA; Monocotyledones; Plant pathogen; Catechol oxidase; Decomposition; Defensive response; Fungi; Dormancy; Gramineae; Weed science; Angiospermae; Fungi Imperfecti; Stramenopila; Weed; Enzyme; Avena fatua; Longevity; Oomycota; Resistance; Deterioration; Seed; Spermatophyta; Oxidoreductases; Caryopsis
• ISSN: 0043-1745; 1550-2759
• DOI: 10.1614/WS-D-10-00123.1

Persistence of the soil seed bank requires both dormancy and resistance to seed decay organisms. However, there is little or no information evaluating biochemical responses of dormant weed seeds to pathogens. Wild oat caryopses were incubated with four pathogenic fungal isolates to evaluate the response of the pathogen defense enzyme, polyphenol oxidase (PPO). Caryopsis PPO activity was induced by three Fusarium spp. isolates previously obtained from whole seeds incubated in the field whereas caryopsis PPO activity was decreased by a Pythium isolate. Fusarium avenaceum isolate F.a.1 caused the greatest PPO induction and was studied in more detail. When whole wild oat seeds were incubated on F.a.1, PPO activity was induced in seeds, hulls (lemma and palea), and caryopses. Incubation of whole seeds on F.a.1 gradually induced caryopsis PPO activity over an 8-d period, whereas incubation of caryopses on F.a.1 over a 4-d period caused a greater and more rapid induction of PPO activity. Very little PPO activity could be leached from untreated caryopses, but nearly all of the induced PPO activity in F.a.1-treated caryopses was readily leached when incubated in buffer. In Western blots, both untreated and F.a.1-treated leachates contained a ∼57-kilodalton (kD) protein, putatively the mature and relatively inactive form of PPO. However, lower molecular weight antigenic proteins between ∼52 and ∼25 kD were strongly induced in F.a.1-treated caryopses, with this induction being correlated with the increase in PPO activity. We hypothesize that dormant weed seeds possess biochemical defenses against pathogens and, more specifically, that proteolysis in the presence of fungal pathogens may release an activated form of PPO from the surface of wild oat caryopses and hulls. Nomenclature: Wild oat, Avena fatua L. AVEFA