| Cadmium(Cd)is one of the common pollutant heavy metals in some rice production areas of southern China.This study aimed to determine the characteristics of Cd uptake and transport in rice plants as well as the distribution of Cd in protein and starch of rice grains.Field experiments and hydroponic experiments were carried out by applying foliar silicon(Si)fertilizer and adding more silicon and zinc(Zn)in nutrient solution,respectively.The main results are as follows:1.The fixation of Cd in roots,synthesis of soluble protein in root cells and absorption of essential elements were promoted with the increase of Si and Zn in the rhizosphere environment.Meanwhile,the uptake of Cd by root protoplasts and transport of Cd from roots to shoots were significantly inhibited.When rice seedlings were exposed to solution with 2.7 μmol·L-1 Cd,adding0.05 and 0.1 mmol·L-1 sulfhydryl Si could reduce the Cd content by 5.4% and 34.7% in rice roots,3.5% and 51.8% in shoots,respectively.Coexistence of Si and Zn had more obvious inhibition on Cd uptake by roots.The treatments of 0.2 mmol·L-1 Zn and 0.05 or 0.1 mmol·L-1 sulfhydryl Si could reduce the Cd content by 27.4% and 68.9% in roots,78.0% and 88.0% in shoots,respectively.The distribution of Cd in cell wall components of roots and the cytosol components of shoots was decreased;the uptake of K,Ca,Fe,Zn by roots and the transportation of them from roots to shoots was promoted when Si and Zn were applied together.2.Applying foliar Si fertilizer with 5 and 10 mmol·L-1 had significant effects on the content of Cd and essential elements in organs of rice.Under Cd-contaminated paddy-rice field,Cd content in late rice culitivar “Huazhan” reached to 0.87 mg·kg-1 in grains and 3.1 mg·kg-1 in rachises;2.2 mg·kg-1,4.0 mg·kg-1 and 35.0 mg·kg-1 in flag leaves,the uppermost internodes and nodes;1.3 mg·kg-1,8.4 mg·kg-1 and 17.8 mg·kg-1 in the second leaves,second internodes and nodes;0.9 mg·kg-1,5.1 mg·kg-1 and12.7 mg·kg-1 in the basal leaves,stems and nodes,respectively.In addition,the content of Si was 172.7 mg·kg-1 in grains.Foliar application of organosilicon with the concentration of 5 and 10 mmol·L-1 could increase the content of Si by 6.2% and 20.7% in grains;reduce the content of Cd by 41.4% and 48.3% in grains,8.8% and 40.3% in rachises,9.1%-54.1% in other organs.Meanwhile,the accumulation of K in grains,rachises and other organs was significantly promoted,the accumulation of Ca,Mg,Fe,Zn and Mn in vegetative organs was also significantly affected.3.Applying 5 and 10 mmol·L-1 foliar organosilicon at flowering stage of early rice had significant influence on the content of Cd and essential elements as well as the distribution of Cdin protein and starch in grains at mature stage.Cd,K,Ca and Zn mainly distributed in protein of grains.Fe and Mn mainly distributed in starch.When the content of Cd was 0.87 mg kg–1 in grains of "Xiangzaoxian 24",the content of Cd in protein was as high as 2.79 mg·kg-1 but Cd content in starch was only 0.54 mg·kg-1.Applying 5 and 10 mmol·L-1 foliar organosilicon at flowering stage could reduce Cd content by 23.4% and 36.8% in grains,17.5% and 18.8% in starch at mature stage,respectively;the content of Fe decrease by 1.59% and increase 33.27% in grain protein;increase the content of Mn and Zn by 18.7% and 28.7%,5.1% and 14.1% in starch,respectively;reduce the content of Fe by 38.40% and 26.67% in starch.The results of XPS analysis showed that the percentage of N,O,P,S and Si in protein was increased,while the percentage of C was decreased. |
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