Transgenic manipulation of polyamine metabolism in poplar

Polyamines are low molecular weight polycations found in all living organisms. They are involved in plant stress response and development. The study was aimed at analyzing the effects of altered polyamine metabolism on the polyamine and related pathways in transformed poplar cells overexpressing a mouse odc cDNA under the control of 2X 35S CaMV promoter. The transgenic cells (line 2E) showed elevated levels of mouse ornithine decarboxylase enzyme activity, several fold higher amounts of putrescine, a small increase in spermidine, and a small reduction in spermine as compared with non-transgenic (NT) cells. The conversion of labeled ornithine into putrescine was significantly higher in the transgenic than the NT cells. The results show that: (a) Transgenic expression of a heterologous odc gene can be used to modulate putrescine metabolism in poplar cells, (b) accumulation of putrescine in high amounts does not affect the native arginine decarboxylase activity, (c) ornithine biosynthesis occurs primarily from glutamine/glutamate and not from catabolic breakdown of arginine, (d) ornithine biosynthesis may become a limiting factor for putrescine production in the odc transgenic cells, (e) assimilation of nitrogen into glutamine keeps pace with an increased demand for its use for biosynthesis, (g) increased putrescine degradation occurs without major changes in the activity of diamine oxidase, (h) rate of spermidine turnover is slower in the transformed cells than the NT cells, and (i) the expression of genes involved in the related pathways may be altered