Napropamide affects auxin levels and modulates gene expression of auxin transporters in Solanum lycopersicum (tomato)

Background: Napropamide is used to control annual grasses and broadleaf weeds. It affects root and shoot development. However, its mechanism of action is inconclusive andhence is classified ingroup 0 herbicides by the Herbicide Resistance Action Committee (HRAC). Objective: This study focused on exploring specific endpoints which could decode some fundamental aspects leading to the inhibitory effect of napropamide on plants. Methods: For rapid in vitro evaluation of morphological parameters, root and shoot length in tomato plant was measured using the International Organization for Standardization (ISO) compliant phytotox system. Indole acids were measured by Salkowski's method and LC-MS/MS and the role of key genes involved in auxin transport was studied with qPCR. Results: In this study, napropamide treatment inhibited root length by 67.6% at 50 mu M, on day 8. Total indole acids content using colorimetric analysis was 13.2 +/- 0.9 mu g mL-1 in treated plants with respect to 10.2 +/- 0.9 mu g mL-1 in control. Detailed LC-MS/MS analysis revealed IAA levels to be 88.8 +/- 16.2 ng mL-1 and 31.3 +/- 6.1 ng mL-1 and indole butyric acid (IBA) levels to be 55.2 +/- 3.4 ng mL-1 and 27.7 +/- 2.5 ng mL-1 in treated and untreated plants respectively. In line with these observations, major auxin transporters AUX1/LAX, PINs showed upregulation of 1.9 to 3.6 folds upon napropamide treatment. Conclusion: This study highlights the effect of napropamide on auxin levels and gene expression and presents a rapid, simple, and user-friendly model for studying inhibitory effect of herbicides in plants.