| Peanut is an important export-oriented agricultural product in China,with a planting area of about 5 million hectares and a total output of 18 million tons,accounting for about 40% of the world,ranking first in the world.Due to the rapid development of modern industry,continuous cropping and excessive use of chemical fertilizers,the problem of soil pollution in farmland in China is becoming more and more serious,especially the heavy metal cadmium.Cadmium has the characteristics of long decomposition period,high mobility,high toxicity and difficult degradation.It is easily absorbed and enriched by crops in production activities,which not only seriously affects the yield and quality of crops,but also harms human health through the accumulation of food chain.About 1%-6% of cadmium remaining in grain and its products is absorbed after ingesting into human body.Cadmium poisoning is caused by accumulation after long-term low-dose intake,and its incubation period can reach 2-8 years,which mainly damages the kidneys,bones and digestive system.Therefore,reducing the intake of cadmium by human body requires reducing the accumulation of cadmium by crops.Different peanut varieties have different abilities of absorbing and enriching cadmium.By screening low-cadmiumaccumulating varieties for popularization and planting in polluted land,the purpose of reducing cadmium content in peanuts and safe production can be achieved.The discovery of low cadmium-enriched germplasm and related genes is the key to cultivate low cadmium-enriched varieties.Through the expression analysis of related genes that cause the difference of Cd accumulation mechanism among peanut varieties,the differences of cadmium accumulation characteristics among peanut varieties are further verified.In this study,six peanut germplasm with different cadmium enrichment characteristics were used to measure physiological indexes at seedling stage,flowering stage and maturity stage with different cadmium treatment concentrations in pot culture,and the expression of related genes under cadmium stress was analyzed.The results are as follows:Effects of Cadmium Stress on Chlorophyll Content and Agronomic Traits of High and Low Enriched Peanuts: Chlorophyll content of six varieties showed a decreasing trend under Cadmium Stress.Chlorophyll content of each variety decreased by 17.2%,14.8%,17.9%,8.8%,10% and 10.5% respectively when the concentration of cadmium was 0.5mg/kg,and the decrease of low enriched varieties was lower than that of high enriched varieties.The height of main stem and the length of lateral branches were also affected by cadmium stress.Compared with the control group,the height of main stem in 0.5mg/kg treatment group and 1.0mg/kg treatment group decreased the most,which was Tang 274(a high cadmium-enriched variety).Effects of cadmium stress on malondialdehyde(MDA)content and antioxidant enzyme system of high and low enriched peanuts: The malondialdehyde(MDA)content of high and low enriched peanuts increased with the increase of cadmium stress,and the malondialdehyde content of high enriched peanuts was always significantly higher than that of low enriched peanuts,indicating that the membrane damage of high enriched peanuts was more serious.The activities of peroxidase(POD)and superoxide dismutase(SOD)in leaves of low-cadmiumenriched varieties were significantly higher than those of high-cadmium-enriched varieties under various stress levels,which indicated that low-cadmium-enriched varieties had active antioxidant systems,making them less susceptible to cadmium poisoning.The content of Pro(proline)increased with the increase of cadmium stress concentration,but the content of Pro first decreased and then increased in different periods.Effect of cadmium stress on cadmium accumulation in high and low enriched peanuts: With the increase of cadmium concentration,the cadmium content in peanut kernel,peanut shell and peanut leaves at different stages increased.Under the stress of 0.5mg/kg cadmium,the cadmium content in seeds of peanut varieties was 0.23mg/kg,0.27mg/kg,0.22mg/kg,0.12mg/kg,0.18mg/kg and 0.15mg/kg,respectively,and the cadmium content of peanut varieties with high cadmium enrichment was higher than that of peanut varieties with low cadmium enrichment.In peanut leaves,the cadmium content increases with the growth of peanuts,and the cadmium adsorbed by peanuts is mainly concentrated in the leaves.Comparison of relative expression of cadmium-related genes between high and low accumulation peanut varieties under cadmium stress: With the increase of cadmium stress time,peanut varieties with different cadmium accumulation ability have great differences in gene expression due to different mechanisms of tolerance to cadmium stress.Ahm TⅡ was expressed in all six peanut varieties.The expression level of Ahm TⅡ in high cadmium enriched varieties was higher than that in low cadmium enriched varieties,and the expression level was the highest in Fuhua 40.To sum up,peanut varieties enriched with low cadmium have less cadmium adsorption,less impact on agronomic traits and less cell membrane damage under cadmium stress,which can more effectively remove free radicals brought by cadmium stress and are more suitable for cultivation in cadmium-contaminated soil. |
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