Effect of Root-Applied Glufosinate-Ammonium on Free Ammonium Accumulation in Tomato Plants
Authors: You Wenqi , Barker Allen V. 
Published: March 2024

Glufosinate-ammonium is herbicidal through inhibition of glutamine synthetase in chloroplasts with the resulting accumulation of phytotoxic levels of unassimilated \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\) \end{document}. The herbicide is applied normally as a foliar spray at concentrations of 100 to 500 mg·L-1. Effect of root-applied herbicide on \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\) \end{document} accumulation was studied in hydroponics. Tomato seedlings (Lycopersicon esculentum Mill.) were grown in a nitrate-based solution (Hoagland no. 1) with herbicide added to active ingredient concentrations of 0, 6, 12, 25, and 50 mg·L-1. In another treatment, an ammonium-based solution was used to assess \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\) \end{document} accumulation from an external source. Harvest and analyses of plant tissue began with first symptoms of phytotoxicity from the herbicide and proceeded at 3-day intervals until plant death with the most extreme treatments. Free \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\) \end{document} was extracted by homogenation of fresh tissues in a 1-m KCl–0.02–m CuSO4 solution. Ammonium was determined by volumetric procedures. By 6 days after treatment, \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\) \end{document} concentrations in tissues increased curvilinearly from nil to 1.5 mg N/g fresh tissue with increases in herbicide in the solution. Classic symptoms of ammonium toxicity were evident. The 50 mg·L-1 herbicide concentration was lethal at 6 days after treatment, and the 25 mg·L-1 concentration was lethal at 12 days when the experiment was terminated. Ammonium accumulation with the lower concentrations of herbicide or with externally supplied \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\) \end{document} was below phytotoxic levels at the end of the 12-day period. Amassment of \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\) \end{document} in foliage followed distinctly different patterns with the herbicide or external supply. Accumulation with the herbicide was mainly in the foliage, whereas with the externally supplied \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\) \end{document}, accumulation in roots exceeded that in shoots with no evidence of phytotoxicity. Results indicate that root-applied glufosinate-ammonium is translocated to shoots where it initiates accumulation of phytotoxic \batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{NH}_{4}^{+}\) \end{document} levels. E-mail barker@pssci.umass.edu