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Location: Molecular Plant Pathology Laboratory

Title: Characterization of apoplast phenolics: Invitro oxidation of acetosyringone results in a rapid prolonged increase in the redox potential

item Baker, Con
item Mock, Norton
item Whitaker, Bruce
item Hammond, Rosemarie
item Roberts, Daniel
item Nemchinov, Lev
item AVER'YANOV, ANDREY - Russian Institute Of Phytopathology

Submitted to: Physiological and Molecular Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/19/2014
Publication Date: 4/1/2014
Citation: Baker, C.J., Mock, N.M., Whitaker, B.D., Hammond, R., Roberts, D.P., Nemchinov, L.G., Aver'Yanov, A.A. 2014. Characterization of apoplast phenolics: Invitro oxidation of acetosyringone results in a rapid prolonged increase in the redox potential. Physiological and Molecular Plant Pathology. 86:57-63.

Interpretive Summary: Bacterial plant diseases cause major damage to crops each year and the cost of controlling them adds greatly to production costs. The plant leaf is the first line of defense against most of these pathogens. Increased knowledge of the molecular interactions that occur when bacteria invade the leaf, can improve resistance and increase yield. In this manuscript we are reporting a previously unknown mechanism that plant cells may currently be using against bacteria. It involves the induction of secondary metabolites at the site of invasion. We found that some of these metabolites can be converted into highly lethal radical forms within minutes. This may present a new strategy for disease control that could be incorporated in plants either through traditional or molecular techniques. This information will benefit plant scientists and breeders who are devising new strategies to improve disease resistance in plants as well as decrease the use of chemical pesticides and antibiotics.

Technical Abstract: In a previous study we observed that if tobacco cell suspensions were inoculated with certain bacterial strains, several hours later the redox potential of the suspensions would increase (oxidative), as much as 100 mV, and in some cases last more than an hour. To discover possible contributors to this oxidative burst, we examined the oxidation of various plant phenolics that were similar to those found in the cell suspensions. Acetosyringone, one of the major extracellular phenolics in tobacco cell suspensions, was unique in causing a prolonged increase in redox potential of more than 100 mV when incubated with H2O2 and peroxidase. The increase in potential appears to be due to a relatively stable radical intermediate. In vitro characterization showed that production of this intermediate is favored by lower pH around 6 and possibly cooler temperatures due to slower kinetics. The intermediate reacts quickly with other phenolics that might be present. Phosphate buffer was substituted for MES buffer which is not redox inert and appeared to extend the periods of increased redox potential by contributing to the regeneration acetosyringone. The results of this study demonstrate that secondary metabolites, many of which are induced upon stress, may not only act as antioxidants, reducing oxidative stress, but some may also produce intermediates able to quickly make the local environmental more hostile to pathogen ingress.