Effects of cadmium, inorganic mercury and methyl-mercury on the physiology and metabolomic profiles of shoots of the macrophyte Elodea nuttallii

Abstract

Macrophytes are known to bioaccumulate metals, but a thorough understanding of tolerance strategies and molecular impact of metals in aquatic plants is still lacking. The present study aimed to compare Hg and Cd effects in a representative macrophyte, Elodea nuttallii using physiological endpoints and metabolite profiles in shoots and cytosol. Exposure 24h to methyl-Hg (23 ng•L-1), inorganic Hg (70 ng•L-1) and Cd (281 µg•L-1) did not affect photosynthesis, or antioxidant enzymes despite the significant accumulation of metals, confirming a sublethal stress level. In shoots, Cd resulted in a higher level of regulation of metabolites than MeHg, while MeHg resulted in the largest number of regulated metabolites and IHg treatment regulated no metabolites significantly. In cytosol, Cd regulated more metabolites than IHg and only arginine, histidine and mannose were reduced by MeHg exposure. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis of data suggested that exposure to MeHg resulted in biochemical changes including aminoacyl-tRNA biosynthesis, glycine, serine and threonine metabolism, nitrogen metabolism, arginine and proline metabolism, cyanoamino acid metabolism, while the treatment of Cd stress caused significant variations in aminoacyl-tRNA biosynthesis and branched-chain amino acids pathways. Data supports an impact of MeHg on N homeostasis, while Cd resulted in an osmotic stress-like pattern and IHg had a low impact. Marked differences in the responses to MeHg and IHg exposure were evidenced, supporting different molecular toxicity pathways and main impact of MeHg on non-soluble compartment, while main impact of IHg was on soluble compartment. Metabolomics was used for the first time in this species and proved to be very useful to confirm and complement recent knowledge gained by transcriptomics and proteomics, highlighting the high interest of multi-omics approaches to identify early impact of environmental pollution.

Metabolic Profiles of Brassica juncea Roots in Response to Cadmium Stress

“…In the present experiment, beta-tyrosine content of B. juncea roots was increased under 48 h Cd stress, in contrast, decreased under 7 d stress. Similar results were reported by Cosio and Renault [36] that tyrosine content of Elodea nuttallii was significantly increased after 24 h of Cd treatment. This suggests that tyrosine may be involved in response to 48 h Cd stress and reduce antioxidant damage in B. juncea through its accumulation.…”

“…Branched amino acids (i.e., leucine, isoleucine, and valine) are considered as precursors for some secondary metabolites, such as alkaloids and glycosides, and participate in both biotic and abiotic stress responses [36]. Previous studies reported that levels of isoleucine and valine were accumulated in Solanum nigrum roots [37] and E. nutalli shoots [36] under Cd stress. In this paper, L-isoleucine was significantly upregulated at T2/T1, but not significantly changed at T3/T1.…”

Metabolomic Responses of Green Alga Chlamydomonas reinhardtii Exposed to Sublethal Concentrations of Inorganic and Methylmercury

“…Similarly, the aminoacyl-tRNA biosynthesis in the aquatic plant Elodea nuttallii was affected by exposure to Cd and MeHg. 40 Aspartate, generated by transamination of oxaloacetate, a tricarboxylic acid (TCA) cycle intermediate, accumulated in cells exposed to IHg and MeHg. Aspartate serves as a precursor for the biosynthesis of other amino acids: asparagine, homoserine, threonine, lysine, and isoleucine, 39 which were also accumulated ( Figure 4).…”

Inorganic Mercury and Methyl-Mercury Uptake and Effects in the Aquatic Plant Elodea nuttallii: A Review of Multi-Omic Data in the Field and in Controlled Conditions

“…In whole shoots, MMHg resulted in the significant regulation of 15 metabolites, while no metabolite was significantly regulated by IHg treatment. In the cytosol, IHg and MMHg exposure regulated three metabolites and four metabolites respectively [43]. Pathway analysis by the Kyoto Encyclopedia of Genes and Genomes (KEGG) of deregulated metabolites revealed that MMHg exposure resulted in biochemical changes in aminoacyl-tRNA biosynthesis, glycine, serine and threonine metabolism, nitrogen metabolism, arginine and proline metabolism, cyanoamino acid metabolism, while IHg treatment caused no significant variations at the pathway level.…”

“…This discrepancy might come from a lower uptake (0.19 µg•g −1 ) of MMHg in those conditions than for IHg (0.67 µg•g −1 ). Nonetheless, a few years later, the effects of the same concentrations (4•10 −10 M IHg, 1•10 −10 M MMHg 24 h resulting in 0.98 and 0.81 µg•g −1 THg respectively) were analyzed by GC-MS-and LC-MS-targeting metabolites in a way that is complementary to other molecular approaches to confirm the Hg cellular toxicity pathway in E. nuttallii (Table 1) [43]. In whole shoots, MMHg resulted in the significant regulation of 15 metabolites, while no metabolite was significantly regulated by IHg treatment.…”