Effect of the pharmaceuticals diclofenac and lamotrigine on stress responses and stress gene expression in lettuce (Lactuca sativa) at environmentally relevant concentrations

[Display omitted] •Translocation of lamotrigine, but not of diclofenac to lettuce leaves.•No direct triggering of oxidative stress but significant changes of gene expression.•Altered gene expression localized in root tissue where diclofenac was present.•Translocated lamotrigine to leaves triggered putative systemic response to roots.•Pharmaceuticals possibly act as zeitgebers affecting the expression of stress genes. Vegetable crops irrigated with treated wastewater can take up the environmentally persistent pharmaceuticals diclofenac and lamotrigine. This study aimed at quantifying the uptake and translocation of the two pharmaceuticals in lettuce (Lactuca sativa) as well as on the elucidation of the molecular and physiological changes triggered by them. Therefore, plants were cultivated in a phytochamber in hydroponic systems under controlled conditions and treated independently with diclofenac (20 μg L−1) and lamotrigine (60 μg L−1) for 48 h. A low translocation of lamotrigine but not of diclofenac or its metabolite 4’-hydroxydiclofenac to leaves was observed, which corresponded with the expression of stress related genes only in roots of diclofenac treated plants. We observed an oxidative burst in roots and leaves occurring around the same time point when lamotrigine was detected in leaves. This could be responsible for the significantly changed gene expression pattern in both tissues. Our results showed for the first time that pharmaceuticals like lamotrigine or diclofenac might act as signals or zeitgebers, affecting the circadian expression of stress related genes in lettuce possibly causing a repressed physiological status of the plant.