Mercury toxicity causes iron and sulfur deficiencies along with oxidative injuries in alfalfa (Medicago sativa)

Abstract

Mercury (Hg) toxicity impairs plant growth and yield. Thus, a better understanding of Hg-induced impairment is needed. In alfalfa, Hg toxicity caused a significant decrease in morphological parameters, as well as increased electrolyte leakage and cell death. The Hg toxicity also adversely affected chlorophyll score and Fv/Fm (maximal quantum yield of PSII) in leaves. This was linked to lower MsIRT1 (Fe-regulated transporter) expression in roots, implying that Hg hinders Fe acquisition in alfalfa. Further, MsSULTR1;2 (sulfate transporter 1.2) and MsSULTR1;3 (sulfate transporter 1.3) were downregulated accompanied by the lower S status in root and shoot, indicating disturbance in S uptake in Hg-treated alfalfa. In silico analysis demonstrated that MsIRT1, MsSULTR1;2 and MsSULTR1;3 proteins are localized in the plasma membrane and showed close partnerships with several Arabidopsis genes, such as FRO2 (ferric reduction oxidase 2), FRU (FER-like regulator of Fe), bHLH39 (stress-responsive bHLH transcription factor) and protein domains (sulfate anion transporter, SLC26A/SuIP transporter) mainly linked to Fe and S uptake, respectively. Finally, photosynthetic disturbance induced by low Fe and S levels along with oxidative stress in cells is related to growth retardation in Hg-exposed alfalfa. These results could be used to develop Hg-tolerant alfalfa plants through breeding or transgenic programs. Supplemental data for this article is available online at https://doi.org/10.1080/11263504.2021.1985005 .