Predicting herbicide movement across semi-permeable membranes using three phase partitioning

Area of Science:

• Agricultural Chemistry
• Plant Biology
• Biochemistry

Background:

• Herbicide efficacy is determined by their ability to penetrate plant cell and organelle membranes.
• Understanding herbicide membrane transport is crucial for predicting their behavior, efficacy, and potential resistance mechanisms in plants.

Purpose of the Study:

• To evaluate an artificial membrane system for predicting herbicide behavior across biological membranes.
• To understand the influence of pH and lipophilicity (log K_ow) on herbicide membrane permeability.

Main Methods:

• An artificial membrane apparatus with varying pH buffers (2.7, 5, 7.4) and a diethyl ether bath was used.
• Five herbicides (glyphosate, 2,4-D, clopyralid, sulfentrazone, glufosinate) with diverse physicochemical properties were tested.
• Herbicide movement and concentration changes were quantified using radioactivity and liquid chromatography-mass spectrometry.

Main Results:

• Herbicide behavior generally aligned with predictions based on their pK_a and log K_ow values.
• Herbicides exhibited greater mobility from acidic to basic conditions, except when their pK_a was below the starting pH.
• Acid trapping was observed for clopyralid, 2,4-D, and sulfentrazone; sulfentrazone and 2,4-D showed high affinity for the nonpolar diethyl ether phase at low pH.

Conclusions:

• The artificial membrane system effectively predicts herbicide behavior at the subcellular level.
• Findings support the role of physicochemical properties (pK_a, log K_ow) in herbicide membrane transport.
• This system can aid in predicting herbicide efficacy, mode of action, and potential resistance evolution.