Summary 1. Adaptive responses to thermal stress typically involve a range of plastic acclimatory responses in ectothermic animals. The mechanisms underlying phenotypic plasticity in inducible cold tolerance are complex and not fully understood. 2. Here we investigated how thermoperiodic cold acclimation affected the cold tolerance and the metabolome of adult Drosophila melanogaster. We have used targeted GC/MS metabolomic profiling to address whether cold acclimation induced specific metabolic changes and affected the dynamics of the homeostatic response following different types of cold stress (acute and chronic). 3. Developmental combined with gradual adult acclimation strongly promoted cold tolerance. This phenotypic variation was associated with significant metabolic changes, among which some sugars, polyamines and metabolic intermediates are fingerprints of these changes. Cold acclimation allowed individuals to maintain metabolic homeostasis, whereas non‐acclimated counterparts suffered from deep and persistent homeostatic perturbations. 4. This study gives a fertile ground for future research in disentangling the role of several metabolites putatively involved in cold acclimation and cold stress response. It also provides insight into the mechanisms by which cold acclimation is achieved in D. melanogaster and gives a basis for elucidating the evolution of plastic responses to thermal variations.

Anthropic changes and chemical pollution confront wild plant communities with xenobiotic combinations of bioactive molecules, degradation products, and adjuvants that constitute chemical challenges potentially affecting plant growth and fitness. Such complex challenges involving residual contamination and mixtures of pollutants are difficult to assess. The model plant Arabidopsis thaliana was confronted by combinations consisting of the herbicide glyphosate, the fungicide tebuconazole, the glyphosate degradation product aminomethylphosphonic acid (AMPA), and the atrazine degradation product hydroxyatrazine, which had been detected and quantified in soils of field margins in an agriculturally intensive region. Integrative analysis of physiological, metabolic, and gene expression responses was carried out in dose-response experiments and in comparative experiments of varying pesticide combinations. Field margin contamination levels had significant effects on plant growth and metabolism despite low levels of individual components and the presence of pesticide degradation products. Biochemical and molecular analysis demonstrated that these less toxic degradation products, AMPA and hydroxyatrazine, by themselves elicited significant plant responses, thus indicating underlying mechanisms of perception and transduction into metabolic and gene expression changes. These mechanisms may explain observed interactions, whether positive or negative, between the effects of pesticide products (AMPA and hydroxyatrazine) and the effects of bioactive xenobiotics (glyphosate and tebuconazole). Finally, the metabolic and molecular perturbations induced by low levels of xenobiotics and associated degradation products were shown to affect processes (carbon balance, hormone balance, antioxidant defence, and detoxification) that are likely to determine environmental stress sensitivity.