Selection And Physiological Characteristics Of High/low Mercury Rice Varieties

In recent years,with the acceleration of China's industrialization process,the problem of mercury pollution in farmland in China has become increasingly serious.Mercury pollution will not only poison the growth of crops,but also enter the human body through the food chain or food web,posing a threat to human health.Therefore,it is of great significance and urgent need to ensure the agricultural safe production of mercury-contaminated soil and to repair the mercury-contaminated soil by using the heavy metal hyperaccumulator.As a big rice producing country and big edible country,China has a long history of rice cultivation and rice planting area,and rice plays an important role in China's social and economic development.This study intends to select rice germplasm resources with large biomass and use its own genetic characteristics to screen for high and low mercury accumulation rice varieties,and then analyze some physiological characteristics of high and low mercury accumulation rice varieties under mercury stress conditions.Physiological characteristics include:Chlorophyll content,Proline content,MDA content,POD activity,SOD activity,CAT activity,GSH and AsA content.The main conclusions are briefly described as follows:1.Screening and identification of high and low mercury accumulation rice varietiesIn this study,48 rice varieties were used as test materials,and hydroponic treatment was performed under the conditions of 0.1mg/L and 10mg/L HgCl₂ for 16days.After the rice reaches the seedling stage,the shoot is harvested,and the shoot biomass and mercury content of each variety of rice are measured,and the tolerance and enrichment coefficient of each variety of rice are evaluated.Exposed to 0.1mg/L mercury,the shoot biomass is between 0.0035-0.0330 g plant^-1 DW,with an average single plant biomass of 0.0122 g plant^-1 DW,the shoot mercury concentration is between 0.0004-0.0038 mg/g,with an average concentration of 0.0019 mg/g.Exposed to 0.1mg/L mercury,the shoot biomass is between 0.0077-0.0182 g plant^-1 DW,the average dry weight per plant is 0.0118 g plant^-1 DW,the shoot mercury concentration is between 0.0133-0.2294 mg/g,and the average concentration is 0.0667 mg/g.Using improved membership function analysis,the tolerance coefficient of 48 rice varieties is between 0.016 and 0.841,and the average mercury tolerance coefficient is 0.3318.The enrichment coefficient of 48 rice varieties is between 0.003 and 0.025,and the average enrichment coefficient is 0.0128.Based on the cluster analysis,using the shoot biomass,mercury content,tolerance coefficient,and enrichment coefficient of the rice as a comprehensive screening index,high-accumulation rice varieties H540 and H535were initially selected.Exposed to 0.1 mg/L mercury,the shoot mercury content was0.0027 mg/g and 0.0030 mg/g,and exposed to 10 mg/L mercury,the shoot mercury content was 0.1748 mg/g and 0.0832 mg/g,and the enrichment index were 0.022 and0.020.Low-mercury accumulation rice varieties H526 and H512.Exposed to 0.1 mg/L mercury,the shoot mercury content was 0.0016 mg/g and 0.0009 mg/g,and exposed to10 mg/L mercury,the shoot mercury content was 0.0433 mg/g and 0.0236 mg/g,and the enrichment index were 0.010 and 0.006.However,the biomass of the four rice varieties was not significantly different,indicating that there were differences in the tolerance of high and low mercury accumulation rice varieties in response to mercury stress.2.Physiological characteristics of high and low mercury accumulation rice varieties in response to mercury stressThe analysis of chlorophyll content in high and low mercury accumulation rice under different concentrations of mercury stress revealed that the chlorophyll content of four varieties of rice decreased under mercury stress,indicating that mercury stress would have an effect on photosynthesis in rice.In addition,the decline of high-mercury-accumulated varieties was more serious than that of low-mercury-accumulated varieties,indicating that the photosynthetic capacity of rice varieties with high-mercury accumulation was more affected by mercury stress than that of low-mercury-accumulated rice.The measurement of MDA content found that there was no significant difference in the content of malondialdehyde,which may be caused by prolonged heavy metal stress,and the ability of antioxidative enzymes and repairing oxidative damage was improved.However,comparing MDA content among different varieties,it was found that low-mercury-accumulating rice varieties suffered more severe oxidative damage than high-mercury-accumulating rice varieties.Compared with the proline content,it was found that the trend of first rise and then decline in the four varieties may be that 5mg/L mercury stress caused damage to plant cells and metabolic functions,leading to a higher proline degradation rate in plants than the synthesis rate.By measuring the activity and sum of antioxidant enzymes and antioxidant substances in rice,it was found that the activities of SOD dismutase in all four varieties of rice decreased,which is similar to that of rice under salt stress,while other antioxidant enzymes and antioxidant Both increased to varying degrees with increasing mercury stress concentrations.In the four varieties of rice,H540 had more significant changes in antioxidant enzymes and antioxidants than the other three varieties of rice under mercury stress,indicating that H540 is a more sensitive genotype,which may mean that H540 is higher tolerance than other varieties.In summary,under the condition of mercury stress,the tolerance and enrichment ability of mercury of the 48 rice varieties tested were significantly different,and high-accumulation rice varieties H540 and H535 and low-mercury accumulation rice varieties H526 and H512 were preliminarily selected.Under different concentrations of mercury stress,rice varieties with high and low mercury accumulation are all poisoned to different degrees,but the effects of mercury stress on rice varieties with high mercury accumulation are greater than those with low mercury accumulation,and in terms of oxidative damage,rice varieties with low mercury accumulation.H540 in four varieties of rice under mercury stress changed more significantly than other three varieties of rice,indicating that is a more sensitive genotype.