Effect Of Zinc On Cadmium Accumulation In Rice And Its Mechanism

Due to human activities and other environmental factors,the current cadmium?Cd?pollution problem is becoming more and more serious,which has already caused serious threats to the food safety production in our country and has become a potential agricultural and global environmental problem.Since zinc?Zn?and Cd belong to the same group of elements and have similar chemical properties,many studies have been made to reduce the Cd content in plants by the application of Zn to alleviate Cd pollution in soil.Although Zn and Cd are known to have antagonistic and synergistic effects in plants,the interaction mechanism between them is still unclear.Therefore,this study analyzed the action mechanism of Zn and Cd in rice from physiological indexes of rice,Zn,Cd content and proteome.The conclusions are as follows:1.Zn fertilizer was applied to mild Cd contaminated soil by soil fertilization and foliar fertilization.The effects of two different fertilization methods on the contents of Zn and Cd in different parts of 9311rice variety were investigated,and the enrichment and transport characterstics were studied.The results showed that the application of Zn fertilizer in the soil was 100 mg·kg^-1,it had no significant effect on the accumulation of Zn and Cd in rice?P>0.05?.When the amount of Zn added was 200 mg·kg^-1 and400 mg·kg^-1,it promoted the accumulation of Zn and Cd in stems and leaves of rice,and the synergistic effect of Zn and Cd accumulation in stems and leaves.When the amount of Zn fertilizer was 400mg·kg^-1,it promoted the absorption and accumulation of Zn,but had no significant effect on the accumulation of Cd.Foliar spraying was applied to the tillering and booting stages of rice,respectively.The sprayed Zn fertilizer promoted the absorption and accumulation of Cd in stems and leaves,and the spraying of Zn fertilizer at the booting stage reduced the Cd content in the treated grain,but the tillering Foliar fertilization had no significant effect on reducing the Cd content in brown rice and polished rice.The enrichment factor of Cd further proved that there was a synergistic effect of Zn and Cd accumulation in stems and leaves;the ability of rice grain to accumulate Cd was weak.From the change of Cd transport coefficient,the ability of leaves to transfer Cd to brown rice is higher than that of stems to transfer Cd to brown rice.The application of Zn fertilizer reduces the transport of Cd from stems and leaves to brown rice,thus reducing the accumulation of Cd in brown rice.2.Using rice varietie 9311 as test material,different concentrations of Zn were applied to rice seedlings treated with low Cd concentration by hydroponic method,and the growth status,Zn and Cd accumulation,and antioxidant system trends of rice seedlings were studied.The results showed that low concentration of Zn inhibited the increase of biomass of Cd-treated rice seedlings and promoted the absorption and accumulation of Zn and Cd by seedlings.100?mol·L^-1 Zn significantly promoted the biomass of Cd-treated rice?P<0.05?,and can significantly inhibit the absorption of Cd by rice;but when the concentration of Zn reaches 3.06×10³?mol·L^-1,Zn has obvious toxic effect on Cd-treated rice.Under different concentrations of Zn,the SOD activity,POD activity and APX activity of rice seedlings increased first and then decreased,while CAT activity was inhibited,and MDA content increased.The low concentration of Zn and Cd synergistically promoted the absorption of Zn and Cd in rice and inhibited the growth of rice;the moderate concentration of Zn and Cd antagonized,inhibited the absorption of Zn and Cd by rice,increased the activity of SOD and POD,and promoted the growth of rice.However,when the concentration of Zn reached a certain value,although Zn and Cd also antagonized,it still had a significant inhibitory effect on rice growth,and damaged the antioxidant system of seedlings.3.The differentially expressed proteins in the roots of normally grown rice and Zn and Cd treated were identified by iTRAQ labeling technique.A total of 4008 proteins were identified,and 332differentially expressed proteins were screened,of which 192 were up-regulated and 140 were down-regulated.GO functional analysis and KEGG pathway analysis showed that the differentially expressed proteins were mainly catalytic active proteins and binding proteins,and were mainly involved in glutathione metabolism,phenylpropanoid biosynthesis,carbon fixation in photosynthetic organisms,cysteine and methionine metabolism,glycolysis/gluconeogenesis,pyruvate metabolism,oxidative phosphorylation.In order to find proteins involved in the transport of Zn and Cd in rice roots,the differential proteins related to ion transport were studied.It was found that there were 7 proteins with different expressions involved in ion transport,which belonged to V-type ATPase and heavy metal P_1B-ATP enzyme?HMA?and plasma membrane ATPase.Among them,A0A1B1ELU7?Gene Name HMA4?may be a protein that has the function of transporting Zn²⁺and Cd²⁺in rice roots.