Inhibition of Chlorophyll Accumulation by Glyphosate

Glyphosate [ N -(phosphonomethyl)glycine] significantly decreased the chlorophyll content of field-grown soybeans ( Glycine max L. Merr. ‘Williams’) within 48 h after a 2.24-kg/ha treatment. In laboratory studies, 0.0001, 0.001, 0.01, 0.1, and 1 mM glyphosate reduced chlorophyll content of 7-day-old etiolated barley ( Hordeum vulgare L. ‘Barsoy’) shoots 8, 12, 25, 49, and 77%, respectively, following 8 h dark incubation and 24 h illumination. Reduction of chlorophyll accumulation ranged from 6% with 0.001 mM glyphosate to 82% with 1.0 mM glyphosate. In studies with 8-day-old etiolated corn ( Zea mays L. ‘Pioneer Brand 3535’) shoots, 0.1, 1.0, and 10.0 mM glyphosate decreased chlorophyll content of corn shoots 24, 42, and 50%, respectively, after 12 h of illumination. The rate of chlorophyll accumulation in corn shoots was significantly reduced 64% by 1.0 mM glyphosate over a 15-h illumination period. These rapid and substantial effects on chlorophyll accumulation suggest that interference with greening may be important in the mechanism of action of glyphosate.