Long‐term cadmium exposure influences the abundance of proteins that impact the cell wall structure in Medicago sativa stems

Abstract

Cadmium (Cd) is a non‐essential, toxic heavy metal that poses serious threats to both ecosystems and human health. Plants employ various cellular and molecular mechanisms to minimise the impact of Cd toxicity and cell walls function as a defensive barrier during Cd exposure.In this study, we adopted a quantitative gel‐based proteomic approach (two‐dimensional difference gel electrophoresis) to investigate changes in the abundance of cell wall and soluble proteins in stems of Medicago sativa L. upon long‐term exposure to Cd (10 mg·Cd·kg−1 soil as CdSO 4). Obtained protein data were complemented with targeted gene expression analyses.Plants were affected by Cd exposure at an early growth stage but seemed to recover at a more mature stage as no difference in biomass was observed. The accumulation of Cd was highest in roots followed by stems and leaves. Quantitative proteomics revealed a changed abundance for 179 cell wall proteins and 30 proteins in the soluble fraction upon long‐term Cd exposure. These proteins are involved in cell wall remodelling, defence response, carbohydrate metabolism and promotion of the lignification process.The data indicate that Cd exposure alters the cell wall proteome and underline the role of cell wall proteins in defence against Cd stress. The identified proteins are linked to alterations in cell wall structure and lignification process in stems of M. sativa, underpinning the function of the cell wall as an effective barrier against Cd stress.

Changes in the Proteome of Medicago sativa Leaves in Response to Long-Term Cadmium Exposure Using a Cell-Wall Targeted Approach

“…Our MS data do not confirm that the inhibitor domain is cut from the PME domain. However, the position on the 2D gel matches with what is predicted for the active protein and are at the same position as those found in M. sativa stems [ 30 ]. In the latter study, cleavage between the inhibitor and the active domain was confirmed based on MS data, indicating that in leaves the inhibitor domain was also cleaved and thus the protein activated.…”

“…Identified proteins were clustered according to their biological function using Blast2Go ( Figure 2 ) and those assignments as well as the number of proteins showing an increased or decreased abundance upon Cd exposure are comparable with results from a similar study on M. sativa stems [ 30 ]. In both studies, results confirm that the enrichment obtained with the used protocol is better than that obtained with comparable protocols, but not 100% and several non-apoplastic proteins, mainly chloroplast targeted, were identified most prominent in the CaCl 2 fraction ( Figure 2 ) [ 30 ]. Those proteins will also be discussed as they are highly abundant in leaves and coherent, significant changes in abundance were observed between replicates and fractions in response to Cd exposure.…”

“…Furthermore to attain the amount of leaf material needed, four to five grams for each replicate, all leaves from young to old were sampled. The visual observation of limited impact of long-term Cd exposure is supported by the fact that the average plant biomass taken from five replicates at the end of the experiment was not significantly different between Cd-exposed (120.32 ± 4.67 g) and control plants (110.65 ± 3.78 g) [ 30 ]. Although long-term experiments as presented here are rather scarce, the high sensitivity of initial growth stages followed by a low impact of the applied stress in adult plants was observed before for other plant species [ 15 , 31 , 32 ].…”

“…Among others, RuBisCO small chain was less abundant in Cd-exposed plants as well as subunits of photosystem I and II. The Cd-induced decreased abundance of photosynthetic proteins was recently reported in M. sativa stems after long-term Cd exposure when analysing cell wall protein-enriched fractions using 2D DIGE [ 30 ]. Likewise as in leaves, RuBisCO small chain, as well as a subunit of photosystem I, were less abundant in M. sativa stems when exposed to Cd.…”

Transcriptome analysis reveals insight into molecular hydrogen-induced cadmium tolerance in alfalfa: the prominent role of sulfur and (homo)glutathione metabolism

“…Cadmium pollution has expanded rapidly in the last hundred years through human activities, such as mining, waste emissions, and fertilizer abuse. Cadmium stress not only affects herbage yield, cell wall structure, and lignification but also poses serious health risks to animals and humans by enrichment through food chains [39]. Previous research has shown the important role of redox status in H 2 -enhanced Cd tolerance and decreased Cd uptake in alfalfa, but little is known about the relative mechanisms involved [27].…”