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ARS Home » Research » Publications at this Location » Publication #85567
Title: OXYGEN METABOLISM IN PLANT/BACTERIA INTERACTIONS: SCAVENGING H2O2 AND PRODUCTION OF OXYGEN BY PEROXIDASE

Author
item Baker, Con
item Deahl, Kenneth
item DOMEK, JOHN - 1275-45-00

Submitted to: Biochemical and Biophysical Research Communications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/1/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: This paper presents evidence of biochemical pathways in which oxygen is metabolized in plants. Plants are able to detect the presence of pathogens well before symptoms can be observed. One of the first plant responses to pathogens is the production of active oxygen somewhat similar to the animal response to pathogens. Recently there has been increased interest in active oxygen levels and their roles in plant/pathogen interactions. A key hurdle in understanding and exploiting this information is the lack of understanding oxygen pathways. This manuscript provides evidence of important chemical mechanisms involving peroxidase and hydrogen peroxide scavenging which need to be considered. This study should be of interest to researchers in the area of plant/pathogen interactions and active oxygen production in plants.

Technical Abstract: The oxidative stress resulting from plant-bacterial interactions in cell suspension cultures is complex and difficult to interpret. Many factors from different regions of the plant cell can either contribute to or reduce oxidative stress. An example of this are the cell wall peroxidases which are complex enzymes capable of catalyzing more than the traditional utilization of hydrogen peroxide to oxidize lignin precursors. Its appears that these enzymes are capable of producing molecular oxygen at the expense of H2O2. To determine how this mechanism might affect oxidative stress, this study utilized purified horseradish peroxidase to better characterize this mechanism under conditions more relevant to our cell suspension system. The pH optimum of both the oxygen production and H2O2 scavenging was fairly broad and in the alkaline region. The apparent Km of the reactions was around 5 mM and 0.1 mM for oxygen production and H2O2 scavenging, respectively. Spectrophotometric scanning of reaction mixtures suggested that at low concentrations of H2O2 (<1mM) the enzyme forms Compound I and II while scavenging H2O2. At higher concentrations of H2O2, the enzyme immediately formed compound III and appeared to become irreversibly inactivted which also coincided with the formation of a new form, C-670, identified by an absorbance peak at 670 nm. It is questionable whether this mechanism plays a significant role in vivo. However, under many in vitro conditions routinely used in oxidative stress studies, this mechanism must be considered when interpreting results.