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

Transgenic rice cell lines transformed with a heterologous cDNA derived from the arginine decarboxylase gene of oat, in an antisense orientation, exhibited significant (P < 0.05) down-regulation of the activity of the endogenous arginine and ornithine decarboxylases, compared to wild type and controls transformed only with the selectable marker (hpt). Changes in enzyme activity 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 that cell lines with low levels of polyamines exhibited normal morphogenic responses. In vegetative tissue at the whole plant level no significant variation (P > 0.05) in polyamine levels was observed. However, we measured significant reductions (P < 0.001) in putrescine levels in seeds derived from three out of five plants analyzed in detail. Thus, simultaneous reduction of the activity of the two alternative enzymes in the early steps of the polyamine pathway results in significant reduction in end-product accumulation in the seeds of transgenic plants.