Over-expression of a cDNA for human ornithine decarboxylase in transgenic rice plants alters the polyamine pool in a tissue-specific manner

We investigated how over-expression of a cDNA for human ornithine decarboxy lase (ode) affects the polyamine pools in transgenic rice. We further inves tigated tissue-specific expression patterns and product accumulation levels of the transgene driven by either constitutive or seed-specific promoters. Our results indicate that: (1) whereas the expression of a heterologous ar ginine decarboxylase (adc) cDNA in rice resulted in increased putrescine an d spermine levels only in seeds, plants engineered to express ode cDNA exhi bited significant changes in the levels of all three major polyamines in se eds and also in vegetative tissues (leaves and roots); (2) there was no lin ear correlation between odc mRNA levels, ODC enzyme activity and polyamine accumulation, suggesting that control of the polyamine pathway in plants is more complex than in mammalian systems; (3) ODC activity and polyamine cha nges varied in different tissues, indicating that the pathway is regulated in a tissue-specific manner. Our results suggest that ODC rather than ADC i s responsible for the regulation of putrescine synthesis in plants.