Effects Of Zinc And Manganese On Cadmium Absorption And Transport In Rice

In recent years,increasing attention has been paid to the problem of cadmium?Cd?pollution in rice produced in Cd-contaminated fields in China.It has become one of research focuses to use comprehensive agronomic measures,such as fertilization technology and leaf regulation,to inhibit the cadmium transport from farmland to aerial and grains in rice plant.Zinc and manganese are essential trace elements for rice growth.In this study,effects and mechanism of inhibiting Cd absorption and transportation in rice plants by increasing the concentration of zinc and manganese in rice rhizosphere or by foliar application with zinc and manganese have been analyzed.The main results are as follows:1.Zinc and manganese can alleviate the toxic effect of Cd on the growth of rice seedlings and maintain the balance of cell metabolism.Compared with control treatment,our results showed that the growth of rice seedlings was significantly inhibited by the addition of 2.7?mol·L^-1CdCl₂ in the culture solution,the content of soluble protein in roots and shoots of rice seedlings decreased,the activity of P-ATPase and V-ATPase also decreased,but the content of free amino acids increased significantly in roots.Adding zinc and manganese in the medium with Cd significantly alleviated the toxic effects of Cd on the rice seedlings,Compared with single cadmium treatment,The content of soluble protein in roots and shoots were increased in the treatment of?Cd+Mn+Zn?,respectively.Meanwhile,the activity of V-ATPase and free amino acid content in roots were restored to the same levels as the control groups.2.Zinc and manganese have significant effects on the uptake and accumulation of Cd and other essential elements in the rice seedlings.It was found that adding 0.8 mmol·L^-1manganese or0.2 mmol·L^-1zinc in nutrient solution significantly inhibited Cd accumulation in rice seedlings.Compared with single cadmium treatment,the coexistence of Mn and Zn reduced cadmium content in roots by 71.9%and in shoots by 49.2%,and eliminated the inhibition of Cd on the absorption and transport of trace elements such as Fe,Mn and Zn.3.Gadolinium?Gd?,an ion channel inhibitor,can significantly inhibite the uptake and transport of cadmium in rice.We found that adding 0.1 mmol·L^-1Gd to the medium with Cd reduced the Cd content in roots and shoots.Adding Gd,Mn and Zn?Cd+Mn+Zn+Gd?at the same time reduced the Cd content in roots by 89.5%and in shoots by 69.9%.Addition of Gd also inhibited the absorption and accumulation of trace elements such as Fe,Mn and Zn in roots,and promoted the synthesis of thiol compounds in roots and shoots.4.Spraying zinc sulfate on leaves can effectively inhibit Cd transport from vegetative organs to rice grains.We found that the cadmium content in the organs of late rice was significantly higher than that of early rice when plant grew in the same Cd-contaminated farmland.The content of Cd in the uppermost nodes of late and early rice was about 10 times higher than that in the rachises and flag leaves.Spraying 5 and 10 mmol·L^-1zinc sulfate on the leaf reduced the Cd content in late rice grains and t in early rice grains.The Cd content in rachises and uppermost node of late rice and early rice was also significantly decreased,and the Cd content in grains was positively correlated with that in uppermost nodes and second nodes.5.Spraying zinc sulfate on leaves have significant effects on the absorption and accumulation of K,Ca,Mg,Mn and Zn for plants.Our result showed that spraying 5 and 10 mmol·L^-1zinc sulfate increased the zinc content in late rice grains by 13.8%and 44.6%,in early rice grains by39.0%and 47.9%,respectively,but had no significant effect on the Mg content in grains.The content of K,Ca and Mn in early and late rice grains was also significantly reduced by spraying zinc sulfate with 10 mmol·L^-1.