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.

Teores de nutrientes em cultivares de café arábica submetidos à deriva de glyphosate

“…) em plantas de girassol, houve inibição de 50% na atividade da redutase férrica nas primeiras horas após tratamento, e inibição completa após 24 horas do tratamento, promovendo sintomas como clorose em folhas jovens (Ozturk et al, 2008). Embora o Fe não faça parte da molécula de clorofila, um dos sintomas de deficiência mais comuns é a clorose de folhas mais jovens, pois o Fe participa da conversão de Mg-protoporfirina IX em protoclorofilida (Taiz & Zieger, 2004 de P na matéria seca foliar no cultivar Topázio, para cada grama de glyphosate aplicado.…”

“…Por esse motivo, é muito comum agricultores atribuí-rem os sintomas de intoxicação pelo glyphosate a distúrbios nutricionais das plantas, como deficiências de N, B, Fe, Zn e Mn (Franzen et al, 2003;Jolley et al, 2004;Römheld et al, 2005;Santos et al, 2007). Tem-se observado, em alguns casos, que aplicações foliares de micronutrientes promovem aumento da produtividade de culturas atingidas pela deriva do glyphosate (Hansen et al, 2004;Ozturk et al, 2008 (Eker et al, 2006;Ozturk et al, 2008); reduziu a atividade da enzima redutase férrica, nitrogenase e redutase do nitrato em plantas de soja convencional (Bellaloui et al, 2006;De Maria et al, 2006); e contribuiu para o menor desenvolvimento do sistema radicular em diversas culturas, dificultando a absorção de P e K, que se dá por difusão (Yamada & Castro, 2007) , ocorrendo menor absorção, transporte e acúmulo (Bernards et al, 2005;Thomas et al, 2007).…”

Physiological Dose-Response of Coffee (Coffea arabica L.) Plants to Glyphosate Depends on Growth Stage

“…If this affirmative is right, we did not observed Ca content increase in both 10 and 45 DAT-plants due Growth probably to low microbial activity in our substrate. However, many different results have been observed in respect to effects of glyphosate on plant nutrition in several crops (Ozturk et al, 2008;Cakmak et al, 2009;Su et al, 2009;Yamada et al, 2009), so that it is not possibly to establish any pattern of plant doseresponses for each nutrient.…”

Characterization of DNA polymorphisms in Caryocar brasiliense (Camb.) in populations with and without thorn at the endocarp by RAPD markers

“…The adaptative answers of the roots differ according to the species. Non-gramineous dicotiledones and monocotiledones induce morphological and physiological differentiations of roots (Marschner and Romheld 1994, Schmidt 1999, Orturk et al 2007. The increase in the capacity of the roots to reduce iron chelants by the induction of ferric reductase in the plasmatic membrane is another answer for the deficiency of iron; the reduction of Fe 3+ in Fe 2+ in the surface of roots is an obligatory process to the acquisition of iron in plants (Marschner andRomheld 1994, Robinson et al 1999).…”