title: Nitrogen supply after removing the shoot apex increases the nicotine concentration and nitrogen content of tobacco plants.
abstract: BACKGROUND
  and Aims High nicotine concentrations in leaves, especially in the upper leaves, offer a serious problem for the cultivation of tobacco (Nicotiana tabacum). Preliminary field experiments showed that rapid mineralization of soil N during late stages of growth may contribute to high nicotine concentrations in leaves.
  
  
  METHODS
  A sand-culture experiment was carried out in the greenhouse. The N supply was controlled during the experiment, and different amounts of 15N were supplied during late stages of growth (after removal of the shoot apex), to investigate the contribution of the N taken up at this time to the N content of and nicotine concentration in tobacco plants.
  
  
  RESULTS
  Addition of 1.6 g or 4 g 15N-labelled NH4NO3 after removing the shoot apex and flushing out the 14N did not increase leaf dry weights; however, it did result in delayed leaf senescence, more lateral bud formation, and an increase in 15N as a proportion of total N, and nicotine-15N as a proportion of total nicotine-N in each organ. The nicotine concentration, 15N and nicotine-15N abundances were increased from the bottom to the top leaves. When more 15N-labelled NH4NO3 was supplied, the nicotine concentration in leaves increased, and so did the 15N abundance in nicotine-N.
  
  
  CONCLUSIONS
  Enhanced N supply in the later growth stages (after removing the apex) increased N content and nicotine concentration in tobacco plants. Nicotine was synthesized de novo during the late growth stages.
authors.affiliation: The Key Laboratory of Plant Nutrition, Ministry of Agriculture, Key Laboratory of Plant-Soil Interactions, Ministry of Education, China Agricultural University, Beijing 100094, China.
authors.forename: X Y
authors.initials: XY
authors.lastname: Xi
authors.forename: C J
authors.initials: CJ
authors.lastname: Li
authors.forename: F S
authors.initials: FS
authors.lastname: Zhang
mesh_terms: D009538:Nicotine / Q000032:analysis / Q000378:metabolism*; D009584:Nitrogen / Q000032:analysis / Q000378:metabolism*; D018515:Plant Leaves / Q000737:chemistry / Q000378:metabolism; D018517:Plant Roots / Q000737:chemistry / Q000378:metabolism; D018520:Plant Shoots / Q000502:physiology*; D018547:Plant Stems / Q000737:chemistry / Q000378:metabolism; D013997:Time Factors; D014026:Nicotiana / Q000378:metabolism*
chemical_list: D009538:Nicotine; D009584:Nitrogen