title: Maize (Zea mays) seeds can detect above-ground weeds; thiamethoxam alters the view.
abstract: BACKGROUND
  Far red light is known to penetrate soil and delay seed germination. Thiamethoxam as a seed treatment has been observed to enhance seed germination. No previous work has explored the effect of thiamethoxam on the physiological response of buried maize seed when germinating in the presence of above-ground weeds. We hypothesised that the changes in red:far red reflected from above-ground weeds would be detected by maize seed phytochrome and delay seed germination by decreasing the level of GA and increasing ABA. We further hypothesised that thiamethoxam would overcome this delay in germination.
  
  
  RESULTS
  Thiamethoxam enhanced seed germination in the presence of above-ground weeds by increasing GA signalling and downregulating DELLA protein and ABA signalling genes. An increase in amylase activity and a degradation of starch were also observed.
  
  
  CONCLUSIONS
  Far red reflected from the above-ground weeds was capable of penetrating below the soil surface and was detected by maize seed phytochrome. Thiamethoxam altered the effect of far red on seed germination by stimulating GA and inhibiting ABA synthesis. This is the first study to suggest that the mode of action of thiamethoxam involves both GA synthesis and ABA inhibition.
authors.affiliation: Department of Plant Agriculture, University of Guelph, Guelph, ON, Canada.
authors.forename: Maha
authors.initials: M
authors.lastname: Afifi
authors.affiliation: Department of Plant Agriculture, University of Guelph, Guelph, ON, Canada.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Lee
authors.affiliation: Department of Plant Agriculture, University of Guelph, Guelph, ON, Canada.
authors.forename: Lewis
authors.initials: L
authors.lastname: Lukens
authors.affiliation: Department of Plant Agriculture, University of Guelph, Guelph, ON, Canada.
authors.forename: Clarence
authors.initials: C
authors.lastname: Swanton
mesh_terms: D000040:Abscisic Acid / Q000378:metabolism; D000681:Amylases / Q000378:metabolism; D018525:Germination / Q000187:drug effects / Q000528:radiation effects; D005875:Gibberellins / Q000096:biosynthesis; D008027:Light; D000073943:Neonicotinoids; D009574:Nitro Compounds / Q000494:pharmacology*; D010078:Oxazines / Q000494:pharmacology*; D057685:Plant Weeds; D012639:Seeds / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D015398:Signal Transduction; D013213:Starch / Q000378:metabolism; D000077922:Thiamethoxam; D013844:Thiazoles / Q000494:pharmacology*; D003313:Zea mays / Q000187:drug effects* / Q000502:physiology / Q000528:radiation effects*
chemical_list: D005875:Gibberellins; D000073943:Neonicotinoids; D009574:Nitro Compounds; D010078:Oxazines; D013844:Thiazoles; D000040:Abscisic Acid; D000077922:Thiamethoxam; D013213:Starch; D000681:Amylases
keywords: ABA; GA; R:FR; amylase; corn; far red light; mode of action; radicle root; red light; seed germination; starch