Some Physiological Effects of Glyphosate on Cocklebur Plants and Cultured Carrot Cells
Nafziger, Emerson D.
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https://hdl.handle.net/2142/71576
Description
Title
Some Physiological Effects of Glyphosate on Cocklebur Plants and Cultured Carrot Cells
Author(s)
Nafziger, Emerson D.
Issue Date
1982
Department of Study
Agronomy
Discipline
Agronomy
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Agriculture, Agronomy
Abstract
Cocklebur plants were grown in nutrient culture in a growth chamber and were treated with 15 (mu)g of glyphosate (N-{phosphonomethyl}glycine) at 13 days of age. Methyl-('14)C-glyphosate was applied in one experiment.
Rapid glyphosate movement to meristematic tissues was followed by growth inhibition and chlorosis in these areas of the plant. Except in treated leaves, stomatal aperture was not affected by glyphosate. Leaf carbohydrate levels were not affected much by the herbicide, but stem and root carbohydrates rose quickly following treatment. The movement of ('33)P from the nutrient solution into the roots was not affected by glyphosate, but P transport to the shoot was drastically curtailed. However, mineral analyses showed no foliar deficiencies. Glyphosate was found to lack auxin activity.
Root tip ATP levels rose by 50% by 8 hr after treatment, then declined over a 4-day period. This pattern suggests the rapid inhibition of an energy-requiring process such as protein synthesis, followed by a general metabolic decline. All of the effects attributable to glyphosate may have resulted from such an inhibition, since growth and related phenomena all depend on a rapid protein synthesis.
Several glyphosate effects were examined using cultured carrot cells grown in liquid medium. Aspartate was found to reduce uptake of the herbicide in a manner quantitatively similar to the reversal of glyphosate growth inhibition by this chemical. This fact, along with the failure of aspartate to alter intracellular ammonia, pH of the growth media, or percentage of live cells, suggests that aspartate reverses growth inhibition by glyphosate mostly by reducing the amount of the herbicide entering the cell. In contrast, some other compounds reported to reverse glyphosate inhibition showed variable effects on glyphosate uptake: succinate had no effect, while phenylylanine reduced uptake by about 30%. Thus, more than one mechanism of glyphosate reversal may operate in these cells.
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