Glyphosate inhibition of ferric reductase activity in iron deficient sunflower roots

Summary

This laboratory study demonstrates that glyphosate, even at sub-lethal drift rates (1–6% of recommended herbicide dose), inhibits ferric reductase activity in sunflower roots, with complete inhibition occurring within 24 hours at the highest rate. The findings provide mechanistic evidence that glyphosate interference with iron acquisition enzymes may explain the increasing incidence of iron deficiency observed in agricultural systems with frequent glyphosate use. The mechanism of enzyme inhibition remains unidentified, and metabolic parameters such as sugar concentration and root respiratory capacity were unaffected by treatment.

Regional applicability

The study was conducted in a controlled laboratory setting on sunflower, a crop not commonly grown in the United Kingdom. However, the findings are potentially relevant to UK arable systems, particularly for dicot and non-grass crops sensitive to iron deficiency; transferability to field conditions and temperate crop species would require additional investigation.

Key measures

Ferric reductase activity; soluble sugar concentration; NAD(P)H oxidizing capacity; glyphosate dose rates (0.32, 0.95, 1.89 mm); time course of enzyme inhibition (6 and 24 hours)

Outcomes reported

The study measured ferric reductase activity in sunflower roots exposed to varying glyphosate drift rates (1–6% of recommended herbicidal dose) under iron-deficient conditions. It documented dose-dependent inhibition of the enzyme, ranging from partial inhibition at lower rates to near-complete inhibition within 24 hours at the highest rate tested.

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