Introduction and expression of a deregulated tobacco nitrate reductase gene in potato lead to highly reduced nitrate levels in transgenic tubers.

Twenty transformed Solanum tuberosum plants issued from five different varieties and carrying a chimeric tobacco nitrate reductase gene (a truncated tobacco Nia2 coding sequence fused to the CaMV 35S promoter) were cultivated in field conditions at INRA Ploudaniel in 1999 and 2000. In 60% of the transgenic plants, the presence of the tobacco Nia2 transcript was detected by RT-PCR. These clones exhibited a drastic decrease in the nitrate content in tubers. Indeed the nitrate content decreased by about 95% in the tubers of transformed plants compared to nontransformed potato plants from the same variety. This decrease was correlated with a modified regulation of NR expression as revealed by a higher chlorate sensitivity of these transgenic lines. Two methods of nitrate content determination in tubers were also compared and were found to give similar results.