Differential effects of root-level exposure to triazine xenobiotics on root development plasticity in Arabidopsis thaliana

International audience; Herbicides and their degradation products contribute to soil pollution and to its impact on soil biodiversity and functioning. Soil herbicide pollution presents characteristics of global planetary threats, with harmful consequences for soil ecology, for ecosystem functions and services mediated by natural plant communities and for crop production sustainability. However, the range and the mechanisms of soil herbicide pollution effects on plants are not fully understood. Effects on roots, as a first line of pollutant exposure, and on root plasticity, as a driver of below-ground ecological processes, must be further characterized. Because of worldwide intensive use of atrazine, of persistence in the environment and of toxicological effects, atrazine and its derived metabolites are typical persistent organic pollutants of soils. The coherent chemical series consisting of atrazine, desethylatrazine and hydroxyatrazine was used to analyse potential effects of triazine xenobiotics on root plasticity processes. Responses to atrazine, desethylatrazine and hydroxyatrazine applied at root level were comparatively analyzed in the model plant Arabidopsis thaliana, which is highly responsive to triazine xenobiotics. We report that triazine xenobiotics, whether as herbicidally active compounds or as degradation products, affect root plasticity in terms of primary root growth, lateral root development and root hair development, and that these effects differentially interact with the light, carbon and cytokinin status of the plant. The adaptive significance of these effects and of their interactions is discussed in terms of toxicity of, or resistance to, residual soil contaminants and in terms of potential cascading impact on plant and ecosystem functioning.