| With the rapid development of industry and agriculture, the harm of heavy metal pollution has become increasingly obvious. The pollution of cadmium is the most severe. Cadmium is easy to be absorbed by main food crops, which will ultimately affect the food safety. There are significant differences in absorption and transfer of cadmium from soil between different rice varieties. Therefore, to plant rice that is low-accumulation of cadmium and passivation have become one of key measurements to make full use of heavy metal contaminated soil so as to guarantee the safety of rice. A large number of studies show that the content of NPT in plant under cadmium stress and cadmium subcellular distribution characteristics are key factors to influence the accumulation and transfer of cadmium and have close relationship to the accumulation of cadmium in rice grains. Sulfur and silicon applied into soil can influence the bio-availability of cadmium and the accumulation of cadmium in crops. However, there is few studies on influence of sulfur and silicon on the transfer of cadmium in crops. Therefore, in this paper, a pot experiment is carried out to research the influence of sulfur and silicon applied in the cadmium contaminated soil on the bio-availability, as well as the influence on NPT content and cadmium subcellular distribution of two different genotypes rice to explore the relationship between the sulfur, silicon and accumulation of cadmium in rice, so as to provide theoretical basis for use low-accumulation of cadmium crops on cadmium contaminated soil. The results are shown as following: 1. Influence of sulfur and silicon on available cadmium content in soilIt is found out from testing the soil availability that, under the condition of this experiment, the influence of sulfur and silicon applied in soil on available cadmium content is mainly reflected by the effect of silicon, while sulfur has little influence on the available cadmium content. The more amount of the silicon the larger the drop of available cadmium. The drops are different for different varieties of crops. In this experiment, Liaoxing 1 has the best effect under S1Si2 condition with a drop of 44.4% and Shenong 315 is 54.8% under S2Si2.2. Influence of sulfur and silicon on form change of heavy metal in soilSilicon is the primary factor influencing form change of cadmium in soil. Sulfur has little influence on the form change of cadmium. With existence of sulfur, the reducing effect of influence of silicon on exchangeable cadmium content. There are differences in different varieties. Liaoxing 1 has the best effect under S1Si2 condition with a drop of 53.9% of exchangeable cadmium content. Shennong 315 has the best effect under S2Si2 condition with a drop of 68.2%. Sulfur and silicon have little influence on carbonate bound cadmium. Other three stable cadmium has relationship with amount of application silicon. The total amount of three kinds of stable cadmium in soil of Liaoxing 1 increases with the application of silicon, while in soil of Shennong 315 under S2 condition, influence of Si2 on stable cadmium content is significantly lower than that of Sil.That shows the effects of silicon on forms of cadmium are different between varieties. The effects of sulfur is not obvious.3. Influence of sulfur and silicon on non-protein thiols (NPT) in stems and leaves of two varieties of riceBased on comparative experimental data, NPT content in leaves of two varieties of rice increased with the increase of application of sulfur, which shows that sulfur can promote the synthesis of NPT. The influence of silicon on NPT first increases and then reduces, but is higher than that of control group under most of conditions, which shows that silicon can also promote the synthesis of NPT. NPT content in Shennong 315 is higher than that in Liaoxing 1 rice under all treatment conditions, which shows that the cadmium-resisting ability of Shennong 315 is higher than that of Liaoxing 1.4. Influence of sulfur and silicon on cadmium subcellular distribution in two varieties of riceSilicon increase the cadmium percentage composition in cell wall of roots, stems and leaves, which shows that silicon can promote the cadmium distribution on cell wall. Sulfur can increase the cadmium content in soluble fraction of cells, which shows that sulfur can promote cadmium to transfer to soluble fraction of cells containing vacuoles. The heavy metal detoxification mechanism in plants with silicon it that strengthening the block of the cell wall to heavy metal. In addition to increasing NPT content, sulfur promotes cadmium to transfer to soluble fraction of cells, which shows that sulfur can increase the effect of vacuolar compartmentalization. The cadmium percentage composition at root cell wall of Shennong 315 is higher than that of Liaoxing 1.5. Influence of sulfur and silicon on transfer and distribution of cadmium in riceUnder the occasion of S0, with the increase of the input quantity of silicon, the content of cadmium in root of two varieties shows a decreasing trend. The cadmium content of Shennong 315 for each treatment is lower than Liaoxing 1. Sulfur would increase the cadmium content and the increasing level of Shengnong 315 is higher than Liaoxing 1. In stems and leaves, the content of cadmium in Liaoxing 1 is higher than Shennong 315 and it is reduced by the increase of silicon. Sulfur makes the content of cadmium in stems show a decreasing trend and the cadmium content in the leaves show a increasing trend. Such effect is more obvious in Liaoxing 1. This indicates that under the treatment of sulfur and silicon, the cadmium capacity transferring to the overground is relatively strong in Liaoxing 1. The lowest treatment of cadmium content in the seed of Liaoxing 1 is S2Si2 and in the Shennong 315 is SOSi2. Both sulfur and silicon could reduce the content of cadmium in the seed of Liaoxing 1 rice. Sulfur could weaken the improvement effect of silicon on the cadmium content in Shennong 315.It turns out from the calculation of transfer coefficient that with the increase of application of sulfur and silicon, the transfer coefficient of both varieties of rice will decrease to reduce the transfer of heavy metal to the overground part. The transfer coefficient of Liaoxing 1 rice is higher than that of Shennong 315, which shows that under the cadmium stress set in this experiment, the concentration of root of Liaoxing 1 is weaker than that of Shennong 315 and more heavy metal is transferred to the overground part. The transfer coefficient of Liaoxing 1 is sensitive to the change of silicon concentration, while the transfer coefficient of Shennong 315 is more sensitive to the change of sulfur concentration.6. Correlation analysis of accumulation in grainsThe result of correlation analysis to shows that a significant positive correlation exists between cadmium accumulation in grains and exchangeable cadmium in soil. The significant positive correlation also exists between cadmium accumulation in grains and the available cadmium content in soluble fraction of stem and soluble fraction of leaf. A negative correlation exists between cadmium accumulation in grains and the total amount of fe-mn oxide bound cadmium, organic-bound cadmium and residual cadmium. A negative correlation not very significant exists between cadmium accumulation in root cell wall, NPT content in leaf and cadmium content in grains, which shows that sulfur and silicon can reduce the accumulation of cadmium in rice grains. However, due to different amount of application of sulfur and silicon, it does not realize the significant level. It is found out from the analysis of cadmium content in grains and application of sulfur and silicon that a negative correlation exists between the cadmium content in grains and application of sulfur and silicon. Influence of silicon on different varieties. There is difference in influence of sulfur on different varieties. Improvement influence of sulfur on Shennong 315 is better than that on Liaoxing 1. |
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