Transgenic aspen plants containing the glutamine synthetase gene GSI from pine have been produced. Among 37 transformed lines, 34 were found to possess GSI. The RT-PCR analysis of GSI transcripts confirmed the presence of specific transcripts in 32 lines. The phenotypic effect of a glutamine synthetase activity in transgenic plants was evaluated by in vitro cultivation of plants at the presence of a sublethal dose (0.5 mg/l) of phosphinothricin, which inhibits this enzyme. It was shown that the sublethal dose of this herbicide provides a predictable inhibiting effect on the nontransformed aspen plants, including the inhibition of their rhizogenesis, whereas transgenic plants demonstrated various responses. In most transgenic lines, we observed an unexpected stimulating effect of low herbicide doses on in vitro rhizogenesis; this effect was manifested through the increased radication frequency, increased average number of roots per plant, and increased total length of roots. © 2010 Pleiades Publishing, Ltd.