The effects of deregulation of NR gene expression on growth and nitrogen metabolism of Nicotiana plumbaginifolia plants

Transformed Nicotiana plumbaginlfolla plants, con stitutively expressing a chimaerlc nitrate reductase gene (nia2 gene transcript fused to the constitutive CaMV 35S promoter), were cultivated in greenhouses at INRA, Versailles (from October to December 1991). They were supplied with either 12 mM or 1 mM NO3−, and given either a 12 h or a 24 h photoperiod. These plants exhibited a nitrate reductase activity in the leaves 25–150% higher than that of the wild-type plants. The physiological consequences of this deregulated expression were further characterized. A main consequence of this over-expression was a decrease in the follar NO3− content (32–47%) and an increase in the glutamine (74–133%) and malate (25–96%) pool sizes compared to the wild-type controls. The higher glutamine content of the leaves of the transgenlc plants resulted in an increase In the total amino acid pool compared to the wild-type even though the levels of other amino acids remained relatively stable. However, the total nitrogen content, protein content and dry matter production were not changed as a result of over-expression of nitrate reductase activity. These results suggest that it is possible to decrease the nitrate content of the leaves, and possibly other organs, in winter crops by this means.