Activation of Host Defense Mechanisms by Elevated Production of H2O2 in Transgenic Plants.

Active oxygen species have been postulated to perform multiple functions in plant defense, but their exact role in plant resistance to diseases is not fully understood. We have recently demonstrated H2O2-mediated disease resistance in transgenic potato (Solanum tuberosum) plants expressing a foreign gene encoding glucose oxidase. In this study we provide further evidence that the H2O2-mediated disease resistance in potato is effective against a broad range of plant pathogens. We have investigated mechanisms underlying the H2O2-mediated disease resistance in transgenic potato plants. The constitutively elevated levels of H2O2 induced the accumulation of total salicylic acid severalfold in the leaf tissue of transgenic plants, although no significant change was detected in the level of free salicylic acid. The mRNAs of two defense-related genes encoding the anionic peroxidase and acidic chitinase were also induced. In addition, an increased accumulation of several isoforms of extracellular peroxidase, including a newly induced one, was observed. This was accompanied by a significant increase in the lignin content of stem and root tissues of the transgenic plants. The results suggest that constitutively elevated sublethal levels of H2O2 are sufficient to activate an array of host defense mechanisms, and these defense mechanisms may be a major contributing factor to the H2O2-mediated disease resistance in transgenic plants.