Damage-induced root nitrogen metabolism in Nicotiana sylvestris. Testing C/N predictions for alkaloid production

"Nitrogen surplus" models for nicotine production induced by leaf damage predict that the observed increase in root nicotine synthesis after leaf damage results from "overflow" metabolism; reduced nitrogen existing in excess of growth requirements is shunted into nicotine biosynthesis. To test the nitrogen surplus model for induced nicotine production, we measured the concentrations of the major N-containing metabolites exported from the roots and the nitrate reductase activity (NRA) of roots and shoots in damaged and undamaged Nicotiana sylvestris plants. Leaf damage: (1) had no significant effect on root or shoot NRA, (2) increased nicotine export and decreased amino-acid and amide export from the roots of NO sub(3)-fertilized plants, and (3) had no significant effect on the export of any N-containing metabolite from the roots of NH sub(4)-fertilized plants. These results are not consistent with the nitrogen surplus model and indicate that leaf damage has a direct infulence on root alkaloid metabolism.