title: The tolerance of grain amaranth (Amaranthus cruentus L.) to defoliation during vegetative growth is compromised during flowering.
abstract: The biochemical processes underlying variations of tolerance are often accompanied by source-sink transitions affecting carbon (C) metabolism. We investigated the tolerance of Amaranthus cruentus L. to total mechanical defoliation through development and in different growing seasons. Defoliated A. cruentus recovered ∼80% of their above-ground biomass and ∼100% of grain yield compared to intact plants if defoliation occurred early during ontogeny, but could not compensate when defoliation occurred during flowering. Tolerance index was higher in the summer season (-0.3) than in the winter season (-0.7). Overall, defoliation tolerance was closely related to phosphoenolpyruvate carboxylase (PEPC) activity in leaves and the subsequent accumulation of starch (∼500 μmol/gDW) and sucrose (∼140 μmol/gDW) in stems and roots. Thus, A. cruentus accumulated sufficient C in roots and stem to allow branching and shoot re-growth after defoliation, but it only possessed sufficient C reserves to maintain <19% seed yield in the absence of new vegetative tissue. Seed size was larger during the warm season but it was not affected by foliar damage. Seed chemical composition was altered by defoliation at flowering. We conclude that A. cruentus defoliation tolerance depends on both, the re-allocation of starch from stem and roots, and the activation of dormant meristems before flowering to generate new photosynthetic capacity to sustain seed filling.
authors: Unidad de Biotecnología e Ingeniería Genética de Plantas, Cinvestav, Unidad Irapuato, México, Km 9.8 Libramiento Norte Carretera Irapuato-León, Irapuato C.P. 36821, Guanajuato, Mexico. Electronic address: ev232@cornell.edu.
authors: Erandi
authors: E
authors: Vargas-Ortiz
authors: Unidad de Biotecnología e Ingeniería Genética de Plantas, Cinvestav, Unidad Irapuato, México, Km 9.8 Libramiento Norte Carretera Irapuato-León, Irapuato C.P. 36821, Guanajuato, Mexico. Electronic address: jdelano@ira.cinvestav.mx.
authors: John Paul
authors: JP
authors: Délano-Frier
authors: Unidad de Biotecnología e Ingeniería Genética de Plantas, Cinvestav, Unidad Irapuato, México, Km 9.8 Libramiento Norte Carretera Irapuato-León, Irapuato C.P. 36821, Guanajuato, Mexico. Electronic address: atiessen@ira.cinvestav.mx.
authors: Axel
authors: A
authors: Tiessen
mesh_terms: D027721:Amaranthus / Q000254:growth & development* / Q000502:physiology; D002241:Carbohydrates / Q000737:chemistry; D002244:Carbon / Q000378:metabolism; D035264:Flowers / Q000502:physiology*; D009829:Oleic Acids / Q000737:chemistry; D010713:Phosphatidylcholines / Q000737:chemistry; D010788:Photosynthesis; D018515:Plant Leaves; D010940:Plant Proteins / Q000378:metabolism; D018517:Plant Roots / Q000254:growth & development; D018547:Plant Stems / Q000254:growth & development; D012621:Seasons; D012639:Seeds / Q000502:physiology; D013696:Temperature
chemical_list: C434585:1-palmitoyl-2-elaidoylphosphatidylcholine; D002241:Carbohydrates; D009829:Oleic Acids; D010713:Phosphatidylcholines; D010940:Plant Proteins; D002244:Carbon
keywords: Carbohydrate reserves; Carbon re-allocation; Compensation; Meristem activation