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info:eu-repo/semantics/published

As a common pollutant, cadmium (Cd) is one of the most toxic heavy metals accumulating in agricultural soils through anthropogenic activities. The uptake of Cd by plants is the main entry route into the human food chain, whilst in plants it elicits oxidative stress by unbalancing the cellular redox status. Medicago sativa was subjected to chronic Cd stress for five months. Targeted and untargeted metabolic analyses were performed. Long-term Cd exposure altered the amino acid composition with levels of asparagine, histidine and proline decreasing in stems but increasing in leaves. This suggests tissue-specific metabolic stress responses, which are often not considered in environmental studies focused on leaves. In stem tissue, profiles of secondary metabolites were clearly separated between control and Cd-exposed plants. Fifty-one secondary metabolites were identified that changed significantly upon Cd exposure, of which the majority are (iso)flavonoid conjugates. Cadmium exposure stimulated the phenylpropanoid pathway that led to the accumulation of secondary metabolites in stems rather than cell wall lignification. Those metabolites are antioxidants mitigating oxidative stress and preventing cellular damage. By an adequate adjustment of its metabolic composition, M. sativa reaches a new steady state, which enables the plant to acclimate under chronic Cd stress.

Little is known about the relationship between nutrition and the circadian clock in plants. The first global transcriptomic study in plants of the response to magnesium deficiency (–Mg) revealed that the circadian clock was affected in the Arabidopsis thaliana model species. Interactions between the circadian clock and Mg status were here investigated in the light of recent knowledge. We highlight the wide disturbances caused by –Mg within the central oscillator and, reciprocally, the probable pervasive influence of the circadian clock on the response to –Mg. We provide evidence that light signalling pathways are likely to be involved in the input of Mg status to the circadian oscillator and that they interact with the circadian clock to coregulate an important part of the transcriptomic response. We further studied PIF3 LIKE 1 (PIL1) because it strongly and early responded, before the core genes of the circadian oscillator, and was a representative regulator of light signalling that interacts with the circadian oscillator. Furthermore, the far-red light-responsive genes, which are related to PIL1, were more enriched among the –Mg-deregulated genes than those responding to red, blue and intense lights. Finally, pil1 mutants had an altered response to –Mg notably by losing the upregulation of PSEUDO-RESPONSE REGULATOR 9, a core circadian oscillator. In short, we have further characterised the interactions between the Mg status and the circadian clock and identified the involvement of light signalling pathways in the response to Mg status. In particular, we have illustrated the role of a light-signalling component in the regulation of the circadian oscillator and physiological processes during Mg starvation., SCOPUS: ar.j, info:eu-repo/semantics/published

info:eu-repo/semantics/published