Exogenous cysteine alleviates mercury stress by promoting antioxidant defence in maize (Zea mays L.) seedlings


Abstract: Mercury (Hg) is one of the most important environmental pollutants that negatively affects plant growth and development. Cysteine (Cys) plays an important role in plant response to various environmental stress factors. In the present study, the alleviation of Hg stress through exogenous Cys treatment to maize seedlings was evaluated. For this purpose, a hydroponic experiment was set up to investigate the effect of HgCI2 (100 μM) and in combination with Cys (200 μM) on plant growth, total chlorophyll content, reactive oxygen species, antioxidant enzyme activities, and mRNA expression levels of some antioxidant genes in maize seedlings. The results showed that HgCI2 treatment significantly decreased both root and shoot growth and total chlorophyll content, also increased the malondialdehyde (MDA), hydrogen peroxide (H2O2), and superoxide levels (O2 .-) in maize seedlings. After treatment with 200 μM exogenous Cys combined with 100 μM HgCl2, root and shoot growth and total chlorophyll content increased and the concentration of MDA, H2O2, O2 .- in seedlings notably decreased and catalase (CAT), glutathione reductase (GR), superoxide dismutase (SOD), and peroxidase (POD) activities in seedlings increased significantly. In addition, HgCI2 treatment alone or combination with Cys markedly increased the root and leaf Hg content. The higher amounts of Hg accumulated in the roots of the seedlings. Furthermore, qRT-PCR results showed that the mRNA levels of CAT, GR, and SOD genes were up-regulated at HgCI2 + Cys treatment groups compared to the HgCI2 treatment alone. The results of the study indicated that exogenous Cys improved resistance to Hg-stress in maize seedlings by activating antioxidant defence system.

Keywords: Antioxidant, cysteine, gene expression, glutathione, mercury

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