| Cadmium (Cd) is a non-essential element and one of the most toxic heavy metals that is present in the soil naturally and from anthropogenic sources, including atmospheric deposition, application of sewage sludge and manures, irrigation water, and in fertilizers and so on. This is a growing concern because Cd in soil can be transferred to plants, resulting in phytotoxicity and threats to animal and human health through the food chain. Cadmium concentrates in the liver, kidney, pancreas, thyroid and bones, and can generate some diseases such as hypertension, bone disease, kidney disorders, liver damage, pulmonary edema, anemia, and so on. Peanut (Arachis hypogaea L.) is a major oil-bearing crop in the world and an important resource of plant protein and a main raw material for food processing. With the increasing of its direct human consumption and food processing, the Cd concentration in peanut kernel has aroused great concern in recent years. China is a main country of the production and exportation of peanut, but the Cd enrichment in peanut kernel is the main obstacle for its peanut export trade and edible safety. Therefore, how to effectively prevent the peanut kernel from Cd contamination has become the hotspot. In this thesis, the combination of soil pot and nutrient solution culture are conducted to study effects of cadmium on peanut qualify and physiological mechanism of peanut and the correlation of between peanut seedlings type 2 metallothionein gene expression and cadmium levels, the majority of results as follows:(1)Pot experiment was conducted to study the effects of cadmium content and seed quality of fifteen genotypes peanut under 12mg Cd/kg treatment. The results indicated that the Cd content in kernel and quality showed significant difference within genotypes (P<0.05). The Cd content in kernel increased significantly (P<0.01) under Cd treatment, especially XA004 increased 86.9 times. The kernel protein content of KB054 decreased 12.3% under Cd treatment, while KC008 increased 13.9%. The Cd content of all peanut kernels in this research was higher than that in GB15201-94 under Cd treatment and can't be eaten directly. It was concluded that XD011 was the less Cd-accumulation genotype among the tested fifteen genotypes peanut, and XA004 was the opposite.(2) Pot experiment was conducted to evaluate the physiological and yield responses of peanut cultivars'HuaYu22 (1)','LuHua14 (2)','FengHua3 (3)','HuaYu20 (4)','HuaYu23 (5)', and'LuHua12 (6)'under 12mg Cd/kg treatment in different growth stages. The results indicated that the peanut treated with Cadmium level of 12mg/kg did not cause obvious visible toxic symptoms, while the antioxidant enzymes activities concluding SOD, CAT, POD showed significant decrease in tested growth stages between control and treatment (P< 0.05) and the content of total chlorophyll decreased significantly in the cadmium treatment samples compared to the control and gradually decreased in the growth stages (P<0.05). These rusults indicated that Cd destroyed the balance of free radical metabolisms, which resulted in increasing MDA content and the relative cell membrane permeability (RMP) which represented the level of lipid peroxidation. The pot yield and pods number per pot in the cadmium treatment generally showed no significant difference compared to the control, whereas the kernel yield and kernel rate per pot showed significant decrease under cadmium stress (P<0.05). And the plump pop stage may be the main stage of Cd effects on peanut yield and the degree of Cd-tolerance was different among varieties. The varieties 3,4 and 6 showed more sensitive than the other varieties. Our results indicated that the MDA, total chlorophyll content and RMP may be more sensitive or indicative than the others under Cadmium stress.(3) Pot experiment was conducted to study the distribution and accumulation of cadmium in five genotypes peanut under different Cd concentration stress. The distribution characteristics were concluded that stalk>root>stem>leaf>seed when the treatment concentration was 0, stem>root>leaf>seed>stalk when it was 3 mg/kg, root>leaf>stem>seed>stalk when the accumulation concentration increased to 12 mg/kg and the leaf>stem>root>stalk>seed when it was increased to 24 mg/kg. The characteristics indicated that with the increasing concentration, the cadmium mainly accumulated in leaves, and the root was not the main accumulated position.(4) Nutrient solution culture experiment was conducted to study the peanut seedling type 2 metallothionein gene expression under different Cd concentration stress. It was successful to establish a precise analysis test method of peanut AhMT2 mRNA expression level with SYBR Green I real time quantitative PCR. PMD18T-AhMT2 and PMD18T-actin recombination plamids were established, and the plasmid copy number and the Cp value have good linear relation. The melting curve peak which can effectively exclude the interference of non-specific signal was single. This method was used to observe and analyze peanut seedlings AhMT2 mRNA expression under different Cd concentration stress, which confirmed the good correlation between Cd concentration and AhMT2 mRNA expression, R2>0.9. |
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