THE EFFECTS OF DEREGULATION OF NR GENE-EXPRESSION ON GROWTH AND NITROGEN-METABOLISM OF NICOTIANA-PLUMBAGINIFOLIA PLANTS

Transformed Nicotiana plumbaginifolia plants, constitutively expressin g a chimaeric nitrate reductase gene (nia2 gene transcript fused to th e constitutive CaMV 35S promoter), were cultivated in greenhouses at I NRA, Versailles (from October to December 1991). They were supplied wi th either 12 mM or 1 mM NO3-, and given either a 12 h or a 24 h photop eriod. These plants exhibited a nitrate reductase activity in the leav es 25-150% higher than that of the wild-type plants. The physiological consequences of this deregulated expression were further characterize d. A main consequence of this over-expression was a decrease in the fo liar 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 transgenic plants resul ted in an increase in the total amino acid pool compared to the wild-t ype even though the levels of other amino acids remained relatively st able. However, the total nitrogen content, protein content and dry mat ter production were not changed as a result of over-expression of nitr ate reductase activity. These results suggest that it is possible to d ecrease the nitrate content of the leaves, and possibly other organs, in winter crops by this means.