A poplar hybrid, Populus tremula x Populus alba, was transformed with the bacterial genes for either glutathione reductase (CR) (gor) or glutathione synthetase (CS) (gshln. When thegorgene was targeted to the chloroplasts, leaf CR activities were up to 1000 times greater than in all other lines. In contrast, targeting to the cytosol resulted in 2 to 10 times the CR activity. CR mRNA, protein, and activity levels suggest that bacterial CR is more stable in the chloroplast. When the gshll gene was expressed in the cytosol, CS activities were up to 100 times greater than in other lines. Overexpression of CR or CS in the cytosol had no effect on glutathione levels, but chloroplastic-GR expression caused a doubling of leaf glutathione and an increase in reduction state. The high-chloroplastic-CR expressors showed increased resistance to photoinhibition. The herbicide methyl viologen inhibited COz assimilation in alllines, but the increased leaf levels of glutathione and ascorbate in the high-chloroplastic-CR expressors persisted despite this treatment. These results suggest that overexpression of GR in the chloroplast increases the antioxidant capacity of the leaves and that this improves the capacity to withstand oxidative stress.

Fluorescence in situ hybridization (FISH) was used to localize two transgenes (gus and bar), carried on plasmids pACT-1F and pUBA, respectively, on mitotic metaphase squashes of T1 plants of the cultivated hexaploid oat Avena sativa L. cotransformed by microprojectile bombardment of embryogenic callus. Among the eight progeny analysed by FISH in each of two lines, we detected plants null, hetero-and homozygous for the two genes in one line, and plants null and heterozygous for the two genes in the other line. Our results demonstrated that in the two independent transformation events, the gus and bar genes had inserted in the same position relative to each other. In each transformation event, the insertions occurred on D satellite (SAT) chromosomes bearing a C genome translocation.

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