Simultaneous reduction of the activity of two related enzymes, involved inearly steps of the polyamine biosynthetic pathway, by a single antisense cDNA in transgenic rice

Transgenic rice cell lines transformed with a heterologous cDNA derived fro m the arginine decarboxylase gene of oat, in an antisense orientation, exhi bited significant (P < 0.05) down-regulation of the activity of the endogen ous arginine and ornithine decarboxylases, compared to wild type and contro ls transformed only with the selectable marker (hpt). Changes in enzyme act ivity were reflected in a marked decrease in the level of putrescine (P < 0 .001) and spermidine (P < 0.01) but not spermine (P > 0.05) in the majority of cell lines analyzed. In agreement with previous results, we confirmed t hat cell lines with low levels of polyamines exhibited normal morphogenic r esponses. In vegetative tissue at the whole plant level no significant vari ation (P > 0.05) in polyamine levels was observed. However, we measured sig nificant reductions (P < 0.001) in putrescine levels in seeds derived from three out of five plants analyzed in detail. Thus, simultaneous reduction o f the activity of the two alternative enzymes in the early steps of the pol yamine pathway results in significant reduction in end-product accumulation in the seeds of transgenic plants.