title: Diel changes in nitrogen and carbon resource status and use for growth in young plants of tomato (Solanum lycopersicum).
abstract: OBJECTIVE
  Modellers often define growth as the development of plant structures from endogenous resources, thus making a distinction between structural (W(S)) and total (W) dry biomass, the latter being the sum of W(S) and the weight of storage compounds. In this study, short-term C and N reserves were characterized experimentally (forms, organ distribution, time changes) in relation to light and nutrition signals, and organ structural growth in response to reserve levels was evaluated.
  
  
  METHODS
  Tomato plants (Solanum lycopersicum) were grown hydroponically in a growth room with a 12-h photoperiod and an adequate supply of NO(3)(-) (3 mol m(-3)). Three experiments were carried out 18 d after sowing: [NO(3)(-)] was either maintained at 3 mol m(-3), changed to 0.02 mol m(-3) or to 0 mol m(-3). Plants were sampled periodically throughout the light/dark cycles over 24-48 h. Organ W(S) was calculated from W together with the amount of different compounds that act as C and N resources, i.e. non-structural carbohydrates and carboxylates, nitrate and free amino acids.
  
  
  RESULTS
  With adequate nutrition, carbohydrates accumulated in leaves during light periods, when photosynthesis exceeded growth needs, but decreased at night when these sugars are the main source of C for growth. At the end of the night, carbohydrates were still high enough to fuel full-rate growth, as W(S) increased at a near constant rate throughout the light/dark cycle. When nitrate levels were restricted, C reserves increased, but [NO(3)(-)] decreased progressively in stems, which contain most of the plant N reserves, and rapidly in leaves and roots. This resulted in a rapid restriction of structural growth.
  
  
  CONCLUSIONS
  Periodic darkness did not restrict growth because sufficient carbohydrate reserves accumulated during the light period. Structural growth, however, was very responsive to NO(3)(-) nutrition, because N reserves were mostly located in stems, which have limited nitrate reduction capacity.
authors.affiliation: Institut National de la Recherche Agronomique, UR 1115 Plantes et Systèmes de Culture Horticoles, Avignon, France.
authors.forename: Ruth
authors.initials: R
authors.lastname: Huanosto Magaña
authors.forename: Stéphane
authors.initials: S
authors.lastname: Adamowicz
authors.forename: Loïc
authors.initials: L
authors.lastname: Pagès
mesh_terms: D002244:Carbon / Q000378:metabolism*; D003624:Darkness; D018551:Solanum lycopersicum / Q000254:growth & development* / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism*; D010788:Photosynthesis / Q000502:physiology
chemical_list: D002244:Carbon; D009584:Nitrogen