CHARACTERIZATION OF ANTISENSE TRANSFORMED PLANTS DEFICIENT IN THE TOBACCO ANIONIC PEROXIDASE

On the basis of the biological compounds that they metabolize, plant p eroxidases have long been implicated in plant growth, cell wall biogen esis, lignification, and host defenses. Transgenic tobacco (Nicotiana tabacum L.) plants that underexpress anionic peroxidase were generated using antisense RNA. The antisense RNA was found to be specific for t he anionic isoenzyme and highly effective, reducing endogenous transcr ipt levels and total peroxidase activity by as much as 1600-fold. Anti sense-transformed plants appeared normal at initial observation; howev er, growth studies showed that plants with reduced peroxidase activity grow taller and flower sooner than control plants. In contrast, previ ously transformed plants overproducing anionic peroxidase were shorter and flowered later than controls. Axillary buds were more developed i n antisense-transformed plants and less developed in plants overproduc ing this enzyme. It was found that the lignin content in leaf, stem, a nd root was unchanged in antisense-transformed plants, which does not support a role for anionic peroxidase in the lignification of secondar y xylem vessels. However, studies of wounded tissue show some reductio n in wound-induced deposition of lignin-like polymers. The data suppor t a possible role for tobacco anionic peroxidase in host defenses but not without a reduction in growth potential.