Abstract
Natural phytotoxic compounds could become an alternative to traditional herbicides in the framework of sustainable agriculture. Nonanoic acid, sarmentine and sorgoleone are such molecules extracted from plants and able to inhibit the growth of various plant species. However, their mode of action is not fully understood and despite clues indicating that they could affect the plant plasma membrane, molecular details of such phenomenon are lacking. In this paper, we investigate the interactions between those natural herbicides and artificial bilayers mimicking the plant plasma membrane. First, their ability to affect lipid order and fluidity is evaluated by means of fluorescence measurements. It appears that sorgoleone has a clear ordering effect on lipid bilayers, while nonanoic acid and sarmentine induce no or little change to these parameters. Then, a thermodynamic characterization of interactions of each compound with lipid vesicles is obtained with isothermal titration calorimetry, and their respective affinity for bilayers is found to be ranked as follows: sorgoleone > sarmentine > nonanoic acid. Finally, molecular dynamics simulations give molecular details about the location of each compound within a lipid bilayer and confirm the rigidifying effect of sorgoleone. Data also suggest that mismatch in alkyl chain length between nonanoic acid or sarmentine and lipid hydrophobic tails could be responsible for bilayer destabilization. Results are discussed regarding their implications for the phytotoxicity of these compounds.
Highlights
Weeds management is a key point for an efficient agriculture and nowadays it mainly relies on the use of herbicides
We can make the assumption that they could interact with lipid membranes and that their efficacy might be linked to this property
A small volume of DPPC dissolved into chloroform-methanol (2:1) was either put alone or mixed with small amounts of nonanoic acid, sarmentine or sorgoleone into a round bottom tube to reach a lipid:herbicide molar ratio of 5:1
Summary
Weeds management is a key point for an efficient agriculture and nowadays it mainly relies on the use of herbicides. It was proven that sarmentine induces destabilization of plasma membrane from cotyledon disks assays (Dayan et al, 2015) This effect was observed with nonanoic acid, again suggesting that both molecules share at least one mode of action. Sarmentine and sorgoleone have a broad spectrum toxicity (Einhellig and Souza, 1992; Dayan et al, 2012, 2015) and share structural similarities: their molecular weight is low (
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