| With the rapid development of heavy industry, the farmland has become cadmium (Cd) contaminated by irrigation of wastewater. application of sewage sludge and cadmium contained phosphate fertilizers. Rice is a main staple food consumed by around 65% population in China, and it readily absorbs and accumulates Cd in the edible part. Cadmium, thus, can enter human body through the food chain, and cause a variety of diseases, even to death. Therefore, the pollution of paddy field, has posed a big threat to both food and ecological safety, which greatly restricted sustainable development of agriculture, and, thus, has arisen increasing public concern. To reduce Cd accumulation and alleviate its toxicity in rice, we systematically studied the influence of zinc (Zn) on rice growth. Cd accumulation and other metal content in rice grains under different Cd levels through hydroponic, pot culture and field experiment. The main results were summarized as follows:1.A pot experiment was conducted to investigate the effects of foliar Zn application at full heading stage on rice growth. yields and metal contents such as Zn, Cd. iron (Fe), copper (Cu). manganese (Mn), magnesium (Mg) and calcium (Ca) in different rice parts under Cd contaimated condition. Correlations of these elements in rice grains were also analyzed. The results showed that elevated soil Cd inhibited rice growth as the fresh weight, dry weight and yield decreased when 2.5 or 5 mg·kg-1 Cd was added to the soil. In brown rice, the Cd content was 0.35 and 0.65 mg·kg-1. respectively, both of which exceeded the food safety standard (0.2 mg·kg-1 Cd). However, with Zn treatment, neither rice growth nor yield was affected. But. Zn content in all plant parts increased with foliar Zn application under all Cd levels. Cadmium content in brown rice also increased by 41.9% with foliar Zn application at 2.5 mg·kg-1 Cd level. However, it decreased by 15.4% at 5 mg·kg-1 Cd level. Further analysis revealed that Cd was significantly correlated with Cu. Mn and Mg, but not Zn in brown rice.2. Under field condition, the effects of foliar Zn application on Cd accumulation of different rice genotypes were studied with different Cd pollution levels, as well as the relationship between Cd and Zn accumulation in brown rice and possible influencing factors. The results showed that Cd and Zn content in rice had a significant genotypic variation. Cadmium content ranged from 0.009～0.078 mg.kg-1, while, Zn content ranged from 20 to 50 mg.kg-1 in all genotypes studied. Cadmium and Zn content was affected by the environmental conditions, genotypes, especially, their interactions effects. For the majority of rice genotypes. Zn content in brown rice increased with foliar Zn application under all the three field experimental locations, especially, the genotype Nipponbare and TN7085, of which Cd content were lower and represented a potential use in Cd polluted area to increase human body zinc content. Cadmium content in brown rice was also affected by foliar Zn application and showed a significant genotypic variation. With foliar Zn application, the Cd content in Xiehui7954 and Zhonahui8006 decreased, and was lower than other varieties. 3. Hydroponic experiments were further conducted to investigate the relationship between Zn/Cd uptake, translocation and root morphology in two rice seedlings. The treatments consisted of two Zn levels (2.0, and 8.0μM) and two Cd levels (0, and 1μM). The seedlings height, biomass, root morphology, and Zn/Cd content of rice were studied at different treat time. The results showed that the TN7085 and Nipponbare had similar characteristics. Compared to control (without Cd). the plant height and shoot biomass were decreased. Besides, root length, root surface area, root number and root volume also exhibited a significant decrease in 1μM Cd treatment. With addition of 8μM Zn into medium solution, plant dry weight. Zn and Cd content, root morphology increased than those in low (2μM) Zn treatment under 1μM Cd level. The root morphological index of 0.0<D≤1.8 mm was significantly affected by Zn/Cd after a treatment for 16 d. However, root morphology of 0.0<D≤0.6 mm was greatly affected by Zn/Cd level and their interactions after a treatment for 35 d. Further analysis revealed that root morphology was positively related with Cd content and accumulation in rice as well as shoot Zn content, but was negatively related with Zn accumulation. With high Zn (8μM) supply, Cd uptake in root and translocation to shoot was enhanced, root growth was improved, and. thus alleviate Cd toxicity on rice seedlings. Besides, it was also noticed that Cd/Zn uptake and accumulation in seedlings was significantly correlated with root morphology. |
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