Damage-induced root nitrogen metabolism inNicotiana sylvestris: Testing C/N predictions for alkaloid production

Abstract

"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 majorN-containing metabolites exported from the roots and the nitrate reductase activity (NRA) of roots and shoots in damaged and undamagedNicotiana 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 NO3-fertilized plants, and (3) had no significant effect on the export of anyN-containing metabolite from the roots of NH4-fertilized plants. These results are not consistent with the nitrogen surplus model and indicate that leaf damage has a direct influence on root alkaloid metabolism.