Apoplast redox metabolism: Effect of acetovanillone (apocynin) and acetosyringone, on their in vitro co-oxidation and redox properties

Authors: Baker, Con; Smith, Jodi; Rice, Clifford

Submitted to: Physiological and Molecular Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/9/2020
Publication Date: 3/10/2020
Citation: Baker, C.J., Smith, J.M., Rice, C. 2020. Apoplast redox metabolism: Effect of acetovanillone (apocynin) and acetosyringone, on their in vitro co-oxidation and redox properties. Physiological and Molecular Plant Pathology. 110:101481. https://doi.org/10.1016/j.pmpp.2020.101481.
DOI: https://doi.org/10.1016/j.pmpp.2020.101481

Interpretive Summary: The plant leaf apoplast, which is the cell wall region just outside the plant cell itself, is the first line of defense against most aerial pathogens. The first responses by the plant and pathogen involve oxidants and antioxidants (reductants) have major effects on the 'redox' potential of the apoplast. Control of the redox potential can determine the outcome of the interaction and resistance or susceptibility of the plant tissue. To begin understanding the effects of these responses on the redox potential, two induced phenolics, acetovanillone (AV) and acetosyringone (AS) were studied. 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: A common response of plant leaves and roots to stress, biotic or abiotic, is an oxidative burst. Reactive oxygen species are produced in the apoplast surrounding the responding cells. A second response that occurs in the apoplast during this period is the production and accumulation of phenolic metabolites. The interaction of these responses would have major effects on the redox potential of the apoplast and affect the outcome of the plant tissue. To begin understanding the effects of these responses on the redox potential, two induced phenolics, acetovanillone (AV) and acetosyringone (AS) were studied in vitro with peroxidase and H2O2, all of which are expected to be present in the apoplast. While both phenolics were good substrates for peroxidase, AV reacted 10x faster than AS. The oxidation of AV resulted in an increase of the redox potential to a maximum of 0.3.5 V. The oxidation of AS resulted in an increase to a maximum of 0.55 V. Interestingly, the redox potential was not proportional to the oxidation of either phenolic. It was found that when present together, co-oxidation occurs with the faster acting AV as a catalyst to oxidize AS. This has an immediate effect on the redox potential. The rate of AS oxidation is dependent on the AV concentration and thus so is the redox potential reaching 4.5 V. We conclude that these phenolics could play a critical role in the regulation of the apoplast redox potential during this early stress response.