title: Glyphosate inhibition of ferric reductase activity in iron deficient sunflower roots.
abstract: Iron (Fe) deficiency is increasingly being observed in cropping systems with frequent glyphosate applications. A likely reason for this is that glyphosate interferes with root uptake of Fe by inhibiting ferric reductase in roots required for Fe acquisition by dicot and nongrass species. This study investigated the role of drift rates of glyphosate (0.32, 0.95 or 1.89 mm glyphosate corresponding to 1, 3 and 6% of the recommended herbicidal dose, respectively) on ferric reductase activity of sunflower (Helianthus annuus) roots grown under Fe deficiency conditions. Application of 1.89 mm glyphosate resulted in almost 50% inhibition of ferric reductase within 6 h and complete inhibition 24 h after the treatment. Even at lower rates of glyphosate (e.g. 0.32 mm and 0.95 mm), ferric reductase was inhibited. Soluble sugar concentration and the NAD(P)H oxidizing capacity of apical roots were not decreased by the glyphosate applications. To our knowledge, this is the first study reporting the effects of glyphosate on ferric reductase activity. The nature of the inhibitory effect of glyphosate on ferric reductase could not be identified. Impaired ferric reductase could be a major reason for the increasingly observed Fe deficiency in cropping systems associated with widespread glyphosate usage.
authors.affiliation: Faculty of Engineering and Natural Sciences, Sabanci University, TUR-34956 Istanbul, Turkey.
authors.forename: Levent
authors.initials: L
authors.lastname: Ozturk
authors.affiliation: Faculty of Engineering and Natural Sciences, Sabanci University, TUR-34956 Istanbul, Turkey.
authors.forename: Atilla
authors.initials: A
authors.lastname: Yazici
authors.affiliation: Department of Soil Science, Faculty of Agriculture, Cukurova University, TUR-01330 Adana, Turkey.
authors.forename: Selim
authors.initials: S
authors.lastname: Eker
authors.affiliation: Faculty of Engineering and Natural Sciences, Sabanci University, TUR-34956 Istanbul, Turkey.
authors.forename: Ozgur
authors.initials: O
authors.lastname: Gokmen
authors.affiliation: Institute of Plant Nutrition, University of Hohenheim, D-70593 Stuttgart, Germany.
authors.forename: Volker
authors.initials: V
authors.lastname: Römheld
authors.affiliation: Faculty of Engineering and Natural Sciences, Sabanci University, TUR-34956 Istanbul, Turkey.
authors.forename: Ismail
authors.initials: I
authors.lastname: Cakmak
mesh_terms: D038181:FMN Reductase / Q000037:antagonists & inhibitors*; D005998:Glycine / Q000031:analogs & derivatives* / Q000494:pharmacology; D006368:Helianthus / Q000187:drug effects* / Q000378:metabolism; D006540:Herbicides / Q000494:pharmacology; D000090463:Iron Deficiencies; D018515:Plant Leaves / Q000187:drug effects / Q000378:metabolism; D018517:Plant Roots / Q000187:drug effects* / Q000201:enzymology*; D013997:Time Factors; D000097797:Glyphosate
chemical_list: D038181:FMN Reductase; D005998:Glycine; D006540:Herbicides; D000097797:Glyphosate; C023903:ferric citrate iron reductase