title: Nitrogen reserves, spring regrowth and winter survival of field-grown alfalfa (Medicago sativa) defoliated in the autumn.
abstract: OBJECTIVE
  The objective of the study was to characterize variations in proline, arginine, histidine, vegetative storage proteins, and cold-inducible gene expression in overwintering roots of field-grown alfalfa, in response to autumn defoliation, and in relation to spring regrowth and winter survival.
  
  
  METHODS
  Field trials, established in 1996 in eastern Canada, consisted of two alfalfa cultivars ('AC Caribou' and 'WL 225') defoliated in 1997 and 1998 either only twice during the summer or three times with the third defoliation taken 400, 500 or 600 growing degree days (basis 5 degrees C) after the second summer defoliation.
  
  
  RESULTS
  The root accumulation of proline, arginine, histidine and soluble proteins of 32, 19 and 15 kDa, characterized as alfalfa vegetative storage proteins, was reduced the following spring by an early autumn defoliation at 400 or 500 growing degree days in both cultivars; the 600-growing-degree-days defoliation treatment had less or no effect. Transcript levels of the cold-inducible gene msaCIA, encoding a glycine-rich protein, were markedly reduced by autumn defoliation in 'WL 225', but remained unaffected in the more winter-hardy cultivar 'AC Caribou'. The expression of another cold-inducible gene, the dehydrin homologue msaCIG, was not consistently affected by autumn defoliation. Principal component analyses, including components of root organic reserves at the onset of winter, along with yield and plant density in the following spring, revealed that (a) amino acids and soluble proteins are positively related to the vigour of spring regrowth but poorly related to winter survival and (b) winter survival, as indicated by plant density in the spring, is associated with higher concentrations of cryoprotective sugars in alfalfa roots the previous autumn.
  
  
  CONCLUSIONS
  An untimely autumn defoliation of alfalfa reduces root accumulation of specific N reserves such as proline, arginine, histidine and vegetative storage proteins that are positively related to the vigour of spring regrowth but poorly related to winter survival.
authors.affiliation: Département de Phytologie, Université Laval, Québec, QC, Canada G1K 7P4.
authors.forename: Catherine
authors.initials: C
authors.lastname: Dhont
authors.forename: Yves
authors.initials: Y
authors.lastname: Castonguay
authors.forename: Paul
authors.initials: P
authors.lastname: Nadeau
authors.forename: Gilles
authors.initials: G
authors.lastname: Bélanger
authors.forename: Raynald
authors.initials: R
authors.lastname: Drapeau
authors.forename: Serge
authors.initials: S
authors.lastname: Laberge
authors.forename: Jean-Christophe
authors.initials: JC
authors.lastname: Avice
authors.forename: François-P
authors.initials: FP
authors.lastname: Chalifour
mesh_terms: D000596:Amino Acids / Q000032:analysis; D018506:Gene Expression Regulation, Plant; D000455:Medicago sativa / Q000737:chemistry / Q000235:genetics / Q000254:growth & development*; D009584:Nitrogen / Q000032:analysis*; D010940:Plant Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000737:chemistry / Q000235:genetics / Q000254:growth & development; D012621:Seasons; D013997:Time Factors
chemical_list: D000596:Amino Acids; D010940:Plant Proteins; D009584:Nitrogen