HAIRY ROOTS OF BRASSICA-NAPUS .2. GLUTAMINE-SYNTHETASE OVEREXPRESSIONALTERS AMMONIA ASSIMILATION AND THE RESPONSE TO PHOSPHINOTHRICIN

Hairy roots of Brassica napus (rape cv. Giant) have been produced that contain the cytosolic glutamine synthetase (GS) gene from Glycine max (soybean). Leaf explants were cocultivated with Agrobacterium rhizoge nes strain A4T harbouring the binary vector pLN16. This vector was con structed by inserting a soybean cytosolic GS cDNA into the multiple cl oning site of pGA643, placing it under the control of the CaMV promote r. Tn addition, the T-DNA region of pLN16 contained a NPTII gene for s election of transformed cells. Transgenic hairy roots grew prolificall y on hormone-free media containing a selective level of kanamycin. Sou thern and northern analyses confirmed the presence of soybean GS DNA a nd transcripts, respectively. These transformed hairy roots also have a greater abundance of the GS polypeptide, approximately 3-6 fold grea ter GS activity and lower levels of endogenous ammonia. Hairy roots pr ovide a useful system for studying responses to phosphinothricin (PPT) . Hairy roots grown in media containing PPT had lower GS activity, gre ater ammonia accumulation and slower growth than controls. The presenc e of the soybean GS gene in the hairy roots reduced these PPT-induced effects and resulted in higher GS activity, lower ammonia levels and f aster growth than in PPT-treated controls. Greater tolerance of PPT wa s also seen in shoots regenerated from the hairy roots displaying elev ated levels of GS activity.