Mechanism Of H₂S-modulating Selenium-mercury Interaction On Non-heading Chinese Cabbage Root Growth Inhition

Selenium(Se)is an indispensable trace element in plants and animals.It has many biological functions and plays an important role in the metabolism of plants and animals.Low concentration of selenium can play a favorable role in the process of plant growth and development,and high concentration of selenium can cause plant oxidative stress,and even inhibit plant growth.Mercury(Mercury,Hg)is one of the most important toxic metal elements in the world,it is a persistent,bioaccumulative and high toxic substance.The antagonism between selenium and mercury has been well known for long,but little is known about the synergistic effects of selenium and mercury interactions on plants.In order to study the mechanism of selenium-mercury interaction on non-heading Chinese cabbage,H2S-specific fluorescent probe WSP-1 was used to track the H2S and research regulation mechanism of H2S on root growth.The mechanism of non-heading Chinese cabbage responding to heavy metal stress was preliminarily revealed by exploring the MTF-MRE system.The results are as follows:Firstly,Selenium(4 ?M)and mercury(1 ?M)mixed treatment group significantly inhibited the growth of seedling roots,reduced the root fresh weight,increased the ROS,O2 ·-and the fluorescence density of dead cells,enhanced the degree of dyeing of H2O2,lipid peroxidation and plasma membrane integrity,increased activity of peroxidase(POD),glutathione peroxidase(GPx)and glutathione transferase(GST),The activity of superoxide dismutase(SOD)enzyme was decreased and the activity of catalase(CAT)had no change.In addition,the content of ascorbic acid(AsA)was reduced and the density of reduced glutathione(GSH)fluorescence was increased.These results suggest that the interaction between selenium and mercury enhances the physiological toxicity of non-heading Chinese cabbage,and also shows the synergistic relationship along the two at this concentration.Secondly,Selenium(4 ?M)and mercury(1 ?M)mixed treatment increased the content of H2S in the roots of Chinese cabbage.The inhibitory effect of root growth increased with the time gradient.The addition of 2 mM NaHS could significantly increase the content of H2S in the roots of non-heading Chinese cabbage,alleviate the inhibition of the growth induced by selenium and mercury,reduce the excessive accumulation of ROS,oxidative damage and cell death.The addition of H2S synthase inhibitor PAG(0.5 ?M)and H2S scavenger HT(16 ?M)could reverse the effect of NaHS.In conclusion,these results indicate that endogenous H2S is involved in the regulation of selenium-mercury treatment in inhibiting the growth of non-heading Chinese cabbage roots.Thirdly,amino acids of the MTF-1 for human and mouse were compared with BRAD in the genome of Brassica rapa L.Four MTF-1 genes were screened and cloned,and the expression of real-time fluorescent quantitative gene was analyzed.The results showed that the sequence of four MTF-1 genes was highly similar to that of the gene selected from the database.The expression of MTF-1 gene was significantly affected by selenium and mercury treatment,while the partial of Rbohs genes in the root area contains typical MREs components.SMART software analysis showed that four MTF-1 amino acids were found for a typical zinc chain structure,and the protein structure analysis showed that the MTF-1 protein in the non-heading Chinese cabbage were similar properties to that of humans and mouse.These results indicate that non-heading Chinese cabbage probably contains an MTF-MRE system that responds to heavy metal stress.