Transgenic manipulation of the metabolism of polyamines in poplar cells

The metabolism of polyamines (putrescine, spermidine, and spermine) has bec ome the target of genetic manipulation because of their significance in pla nt development and possibly stress tolerance. We studied the polyamine meta bolism in non-transgenic (NT) and transgenic cells of poplar (Populus nigra x maximowiczii) expressing a mouse Orn decarboxylase (odc) cDNA. The trans genic cells showed elevated levels of mouse ODC enzyme activity, severalfol d higher amounts of putrescine, a small increase in spermidine, and a small reduction in spermine as compared with NT cells. The conversion of labeled ornithine (Orn) into putrescine was significantly higher in the transgenic than the NT cells. Whereas exogenously supplied Om caused an increase in c ellular putrescine in both cell lines, arginine at high concentrations was inhibitory to putrescine accumulation. The addition of urea and glutamine h ad no effect on polyamines in either of the cell lines. Inhibition of gluta mine synthetase by methionine sulfoximine led to a substantial reduction in putrescine and spermidine in both cell lines. The results show that: (a) T ransgenic expression of a heterologous ode gene can be used to modulate put rescine metabolism in plant cells, (b) accumulation of putrescine in high a mounts does not affect the native arginine decarboxylase activity, (c) Orn biosynthesis occurs primarily from glutamine/glutamate and not from catabol ic breakdown of arginine, (d) Orn biosynthesis may become a limiting factor for putrescine production in the odc transgenic cells, and (e) assimilatio n of nitrogen into glutamine keeps pace with an increased demand for its us e for putrescine production.