Effect of Ammonium Sulfate on Absorption of Imazethapyr by Quackgrass (Elytrigia repens) and Maize (Zea mays) Cell Suspension Cultures

Abstract

Field trials indicated that addition of ammonium sulfate to imazethapyr plus nonionic surfactant increased quackgrass control, especially at low imazethapyr rates. In greenhouse experiments, approximately twice as much imazethapyr was absorbed by quackgrass leaves when the herbicide was applied in combination with nonionic surfactant plus ammonium sulfate than when the herbicide was applied with nonionic surfactant alone. Black Mexican Sweet maize (BMS) suspension-cultured cells were used to evaluate the effects of ammonium sulfate and nonionic surfactant on cellular absorption of imazethapyr in the absence of a cuticular barrier. Imazethapyr absorption by BMS cells was diffusion-mediated, energy-dependent, and exhibited a pH optimum of approximately 3. Over the concentration range of 0.1 to 10.0 μM, the equilibrium concentration of imazethapyr in BMS cells was a linear function of the external concentration. Addition of ammonium sulfate to the external medium of BMS cells enhanced both the rate of imazethapyr uptake and medium acidification. There was a linear correlation between the ability of ammonium sulfate (0.5 to 10 mM) to promote medium acidification and imazethapyr uptake by BMS cells. The ammonium sulfate-induced stimulation of imazethapyr absorption in BMS cells was sensitive to plasma membrane adenosine triphosphatase inhibitors (sodium vanadate, diethylstilbestrol), the uncoupler carbonyl cyanide m-chlorophenylhydrazone, and energy metabolism inhibitors (sodium azide, nitrogen gas), demonstrating that this effect was dependent on ATP production and the functioning of the plasma membrane ATPase. It is hypothesized that cytoplasmic acidification in BMS cells due to ammonium assimilation stimulates the plasma membrane ATPase to pump protons across the plasma membrane which in turn acidifies the cell wall promoting cellular accumulation of imazethapyr by ion-trapping. Cell wall acidification due to ammonium assimilation may contribute to the ability of ammonium sulfate to enhance the efficacy of imazethapyr and other foliar-applied herbicides.

Plants as sources of cations antagonistic to glyphosate activity

“…Translocation could also be improved by increasing the uptake of glyphosate into the symplast. In cell culture, AMS increases the permeability of the cell membrane to ions30, 34 and can enhance cellular uptake of several herbicides, including glyphosate, imazethapyr and cycloxydim 35–37. It is important to point out, however, that other studies using isolated cells have found no effect of AMS on glyphosate uptake across the plasmalemma 38, 39.…”

Lower formulation pH does not enhance bentazone uptake into plant foliage

“…The mechanism of absorption of weak acid herbicides into plant cells has been extensively investigated (Van Ellis & Shaner 1988;Sterling et al 1990;Gronwald et al 1993). Generally, the absorption is pH-dependent with the greatest amount of herbicide penetration occurring at acidic external pH.…”

“…It is generally believed that for such chemicals, uptake into plant tissues is greater at lower carrier pH, due to a higher proportion of the molecules being present in an undissociated form. However, data supporting this statement were mostly obtained with plant tissues immersed (Van Ellis & Shaner 1988;Liu 1993) or cultured cells incubated (Sterling et al 1990;Liebl et al 1992;Gronwald et al 1993) in a solution of unformulated weak acid herbicides.…”

Influence of Water Hardness and Co-applied Herbicides on Saflufenacil Efficacy

“…However, saflufenacil treatments with DAS did not show any differences in control of common lambsquarters compared to saflufenacil in deionized water without DAS. Several studies have suggested that DAS increases the foliar absorption of herbicides, which consequently increases efficacy (6,7,9). Moreover, according to the label of saflufenacil, this product must be applied with DAS and methylated seed oil (2).…”