| Compared with the other trees, poplar (Populus spp.), playing the most significant role in national economy, is one of the important trees for artificial protection forest. For long period, poplars are susceptible to many plant pathogens. That has been causing inestimable loss to national economy. Meantime, its overwhelming devastation to ecological environment was uncompensated. Utilizing the genetic engineering techniques seems a practical way to improve disease resistance for poplars. As a threatening toxin, oxalic acid secreted by many fungi correlated to their pathogenicity, which was already reported in ten genera for instance in Sclerotinia sclerotiorum. The introduction and expression of gene encoding enzymes that degrade oxalic acid is a potentially powerful strategy to enhance resistance to the fungi that secrete oxalic acid. Moreover, H2O2 produced by the degradation of oxalate acid can have a direct antimicrobial effect and serve s signal for the regulation of hypersensitive reaction and the activation of plant defense mechanisms. This research will mainly focus on with the method of Agrobacterium tumefaciens-mediated transformation, the Oxalate oxidase (OxO) gene will be tried to be transferred into good poplar species, in order to obtain the enhanced extensively resistant transgenic poplar lines. Engineered Agrobacterium tumefaciens strain LBA4404 will be used, which contained plant expression plasmid OxO-pGPTV-KAN., in which OxO gene gf2.8 and kanamycin resistance selectable gene nptII were already constructed. Poplar 84K and triploid white poplar (Populus tomentosa Carr.) will be transformed as the receptor plants. The specific studies were as belows: 1. The high frequency regeneration system for poplar 84K leaves explants was established. 2,4-D was reported as the function of both inducing calli and adventitious bud for the first time. The optimal induction medium for poplar 84K leaves explants was MS + 1.0～1.5 mg/L 6-BA + 0.02 mg/L 2,4-D. 90%～100% budding percentage and 20 average adventitious buds per leaf were obtained. 2. The aseptical seedlings triploid poplar was obtained from the differentiation of axillary bud and micro-propagation system was established. The optimal induction medium for triploid poplar leaves explants was 1/2 MS + 0.75 mg/L 6-BA + 0.3 mg/L NAA + 20 g/L sucrose. 60% budding percentage and 3～4 average adventitious buds per leaf were obtained. 3. Kanamycin sensitivity tests for both poplar 84K and triploid white poplar were conducted. For poplar 84K the optimal selecting pressure for both adventitious bud and root induction were 20 mg/L, while 15 mg/L for triploid white poplar. 4. The factors possibly affecting transformation frequency were studied. The basic transformation way was as follows: pre-culture of leaves explants on bud induction medium for 2～3 days ? infection for 5～10 min. in diluted bacterium suspension (OD600 = 0.5) ? co-culture on bud induction medium for 4～5 days ? culture for eradicating overgrowth Agrobacterium (on bud medium with appropriate Cefotaxime or Carbenicillin) for about 10 days ? culture on selective root induction medium (root induction medium with appropriate concentration antibiotics), selecting till shoot rooted (40～60 days). 5. PCR identification of the kanamycin resistant regenerated shoots. 71 transformed polars 84K were obtained. Unfortunately, none of them were positively transgenic shoots after PCR identification.
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