Glyphosate Inhibits Photosynthesis and Allocation of Carbon to Starch in Sugar Beet Leaves
Application of glyphosate (N-[phosphonomethyl] glycine) to exporting leaves of sugar beet (Beta vulgaris, L.) during the day lowered stomatal conductance and carbon fixation. Allocation of newly fixed carbon to foliar starch accumulation was nearly completely inhibited, being Dec.reased by the same amount as net carbon fixation. In contrast, Dec.reasing net carbon fixation in untreated leaves by lowering CO2 concentration caused starch accumulation to Dec.rease, but only in the same proportion as net carbon fixation. Shikimate level increased 50-fold in treated leaves but the elevated rate of carbon accumulation in shikimate was only 4% of the Dec.rease in the rate of starch accumulation. Application of steady state labeling with 14CO2 to exporting leaves confirmed the above changes in carbon metabolism, but revealed no other major daytime differences in the 14C-content of amino acids or other compounds between treated and control leaves. Less 14C accumulated in treated leaves because of Dec.reased fixation, not increased export. The proportion of newly fixed carbon allocated to sucrose increased, maintaining export at the level in control leaves. Returning net carbon exchange to the rate before treatment restored starch accumulation fully and prevented a Dec.rease in export during the subsequent dark period.
American Society of Plant Biologists
Geiger, Donald R.; Kapitan, Shelly W.; and Tucci, Michelle A., "Glyphosate Inhibits Photosynthesis and Allocation of Carbon to Starch in Sugar Beet Leaves" (1986). Biology Faculty Publications. 79.