Effects of Haloxyfop on Corn (Zea mays) and Soybean (Glycine max) Cell Suspension Cultures

Abstract

To investigate the mode of action of a grass-specific herbicide, haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} was added to corn and soybean cell suspension cultures containing metabolic intermediates such as sucrose [14C-U], sodium acetate [14C-1,2], or L-leucine [14C-U]. Death of the corn suspension cells occurred within 3 days after haloxyfop was added at a concentration of 1.0 μM to supplemented Murashige and Skoog's medium. At 0.1 μM haloxyfop, 14C-sucrose uptake and 14C loss due to respiration of the corn cells declined without a significant reduction in cell fresh weight, cell viability, cellular ATP level, free sugar content, cell wall materials, or level of glycolytic intermediates. The proportions of sucrose, glucose, and fructose in the free sugar fraction were not affected. However, the 14C-labeled free amino acid level was increased. During a 24-h incubation period, incorporation of leucine [14C] as a precursor revealed that haloxyfop did not inhibit protein synthesis. Incorporation of acetate [14C-1,2] showed that total lipid synthesis was inhibited by 42% at 0.1 μM haloxyfop (sublethal). Similar responses were observed in the soybean suspension cells; however, the calculated 50% lethal concentration (LC50) was 47 times higher than for corn cells. The results of this study suggest that the site of action of haloxyfop is located where metabolic intermediates enter the Kreb's cycle and lipid synthesis. Glycolysis is not inhibited.