| Cadmium (Cd) is a kind of heavy metals trace elements and widespread in nature. It is the main pollutants of heavy metals in soil, being classified as the first of five pollutants of heavy metals (Cd, Hg, As, Cr and Pb). It is also the first of12global dangerous chemicals from the United Nations Environment Program. According to statistics, up to30000t per year Cd are released into the environment from the industrial waste, fertilizer and automobile exhaust etc.82%to94%of them are going to soil. In China, up to680t per year of Cd are discharged to the environment from industrial waste. The garden soil with Cd content exceeding national environmental quality standards Ⅱ accounts for24.1%. Cadmium has become one of the main types of heavy metal contamination of soil and vegetables. Engineering method, phytoremediation and agronomic regulation are common used to control Cd pollution. In recent years, Agronomic control methods which use antagonistic effect of competitive cation and Cd2+to control Cd uptake and transport to the edible parts of the crop has become the focus of cadmium pollution studies. Lanthanum (La) belongs to the lanthanides, is one of the most active rare earth metals. Selenium (Se) is an essential trace element. Both Se deficiency and excess will lead to varies symptoms, while appropriate Se has anticancer effects on the human body. Lanthanum and Se have antagonism effect to cadmium, lead, mercury and other heavy metals. Suitable concentrations of La and Se can alleviate toxicity of heavy metal to plants, and then improve plant resistance to stress. At present, there are many studies on the interaction of lanthanum and selenium with cadmium, but the result remained open.Tomato (Lycopersicon esculintum Mill.) and cucumber (Cucumis sativus L.) are two common vegetables people liked and rich in nutrients. However, they are while also with high Cd enrichment thought the pre-trial. Cadmium content of fruit in tomato and cucumber is much higher than the national standard limit for cadmium in vegetables (0.05mg·kg-1). Excess Cd in tomato and cucumber will not only affect the taste and nutritional quality, but also affect human health through the food chain. Base on the pre-trial, the author compares two varieties of tomato (4641and Yufen109) and two varieties of cucumber (Yanbai and Jinyou1). In the same cadmium contaminated soil (20mg·kg-1), by spraying LaCl3(0,10and20mg·L-1) and Na2SeO3(0,0.5and1.0mg·L-1) on leaves, the author observes its influence to the plants growing, yield and quality, Cd chemical form in fruit and Cd accumulation in plant, aiming to providing a theoretical basis of rational distribution of vegetable culture in Cd contaminated soil. The main results are as follows:1. The dry weight of plants, fruits, roots, stems and leaves increased in both varieties of tomato. With the increasing La concentrations, the CAT activity in roots in both varieties and the SOD activity, the POD activity in4641’s roots and leaves decreased till the lowest value at10mg·L-1La. The CAT activity in4641leaves decreased with the increasing of La concentration, while the CAT and SOD activity in leaves of Yufen109increased. The chemical form of Cd in the fruits was in order of FNacl>FHAC>FHCl>FR>Fw.Appropriate amount of La reduced Cd concentration in the tomato fruits. The Cd accumulation in plants was in order of leaves> stems> fruits> roots. By spraying La, Cd concentration of leaves, stems, roots and fruits in both varieties reduced by13.7%-31.9%,9.5%-30.6%,10.8%-44.5%and19.4%-37.0%, respectively. The Cd accumulation in fruits of4641was higher than that in Yufen109and the total Cd accumulation in plants of4641was lower than that in Yufen109no matter with spraying La or not. Except the content of vitamin C and amino acids in Yufen109, nitrates content in two varieties of tomato were lower than the control when concentration of La at20mg·kg-1, the other indicators of quality in La treatments were higher than in the control.2. Exogenous La increased the CAT, SOD and POD activity in both varieties of cucumber. The dry weight of leaves, stems, root, fruits and the plants also increased in the presence of La. The influence of La to the plants dry biomass in Jinyoul was higher than that in Yanbai. Exogenous La increased the antioxidant enzyme activity in leaves and roots of cucumber, which may be one of physiological mechanisms to enhance resistance of Cd and increased dry weight of crops. The total Cd and different forms of Cd in fruit of both varieties of Cucumber were decreased with the increase of La. However, with the increasing of La concentration, the total Cd and FR decreased first and then increased in both fruits. Exogenous La reduced Cd concentration in leaves, stems, roots and fruits in both varieties of cucumber by6.0%-10.2%,8.9%-23.5%,4.0%-29.2%and32.0%-49.8%, respectively. After spraying La, Cadmium concentration in fruits, Cd accumulation and the total Cd in Jinyou1were higher than that in Yanbai. With the increasing of La concentration, the content of vitamin C and amino acid in the two varieties of cucumber increased. The Nitrate content in Yanbai and the amino acids content in Jinyou1increased first and then decreased. But the sugar percentage in two varieties of cucumber and nitrate in Jinyoul decreased first and then increased.3. After spraying Se, the dry weight of roots, stems, leaves, fruits and plants in the two varieties of tomato increased first and then decreased and reach the peak at10mg·L-1Se. The CAT, SOD and POD activities in the two varieties of tomato showed different trend with the increase of Se. The concentration of Cd in fruits was in order of FNaCl> FE> FR> FHAC>FHCl>Fw-The total Cd and concentrations of different Cd chemical forms of fruits in both varieties of tomato decreased after spraying Se. With the increase of Se concentration, the total Cd of fruits in both varieties of tomato decreased first and then increased, and the lowest value was found at10mg·kg-1Se. Whether La was sprayed or not, the total Cd in fruits of Yufen109is higher than that in4641. Spraying Se reduced Cd concentrations in leaves, stems, roots and fruits in both varieties of tomato by7.3%-41.9%,9.8%-30.9%,24.5%-48.5%and14.4%-37.1%, respectively. Whether La was sprayed or not, Cd concentration and Cd accumulation in4641is higher than that in Yufen109. The content of vitamin C and amino acid in the two varieties of tomato increased first and then decreased with the increase concentrations of Se. Selenium promoted content of reducing sugar in both varieties of in tomato. The low concentration of Se reduced the nitrate content in both varieties of in tomato.4. After spraying Se, the dry weight of leaves, stems, roots and fruits, and Cd concentration and Cd accumulation showed significant differences between the two varieties of cucumber. With the increase of Se concentration, the content of MDA of leaves is increased in Yanbai, while decreased in Jinyoul. The content of MDA in roots of Yanbai increased first and then decreased with the increase of Se concentration but it was vice versa for Jinyoul. Selenium reduced the concentrations of different Cd chemical forms. Spraying Se reduced Cd concentrations in leaves, stems, roots and fruits in both varieties of cucumber by3.2%-17.9%,14.6%-28.2%,5.1%-18.5%and60.6%-75.8%, respectively. Whether La was sprayed or not, The total Cd of plant in Yanbai is lower than that in Jinyou1. Spraying Se produce different effects on the content of vitamin C, amino acid, reducing sugar and nitrate in the two varieties of cucumber. |
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