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A cationic peroxidase gene (Shpx6a) of a forage legume species, Stylosanthes humilis, was transferred to poplar (Populus tremula) in antisense orientation under the control of 35S RNA promoter of cauliflower mosaic virus. Transformed plants were regenerated on selective media after co-cultivation of poplar stem explants with Agrobacterium tumefaciens and integration of transgenes was confirmed by PCR and Southern hybridization analyses. Analyses of selected transgenic plants showed reductions in total leaf peroxidase activity which was 50% to 70% of that measured in untransformed control plants. Transgenic poplar plants with reduced leaf peroxidase activity had 10-20% lower lignin content than control plants. Although which isoform of poplar peroxidase (s) has been inhibited by 35S-Shpx6a antisense construct is not clearly known, our results suggested the possibility of manipulation of lignin content through inhibition of lignin-specific peroxidases.

Tissue culture of Populus tremula Dursunbey 2 clone from stem expiants was established. peroxidase gene isolated from Stylosanthes humilis (Shpx6), in antisense orientation was transferred to poplar via Agrobacterium tumefaciens. The effects of Shpx6 gene leads to modification of total peroxidase activity and total lignin amount. A reduction of total peroxidase activity for 50% and total lignin amont for 20% was observed in transgenic plants compared with control plants. The results obtained here, could be useful for utilization of poplar in paper and pulp industry.

Populus tremula was transformed using Agrobacterium tumefaciens with antisens O-metyltransferase gene from Stylosanthes humilis (pOMT8), which is showing 83% homology with COMT gene from poplar. In four out of ten transgenic plants OMT activity has been downregulated for 30–39%, however peroxidase activity was 100% higher compared with controls. While the lignin amount in transgenic plants was not changed, lignin composition were modified. Results indicate that it is possible to downregulate endogenous OMT activity and modified lignin composition through the introduction of heterologous consract from Stylosanthes humilis in Populus tremula.