Studies On The Physiological Effects Of Zinc Under Cadmium Stress On Rice Growth And The Characteristics Of Translocation And Accumulation Of Cadmium In Rice

The farmland affected by cadmium(Cd)pollution is growing in our country,and this has presented a serious challenge to the safety of our agricultural products and the ecological environment.Rice is a staple cereal crop in China,it has a strong tolerance to Cd.Rice is also one of the bulk grains which are easy to absorb and accumulate Cd.Thus,the rice Cd pollution has become the focus of public concern.Zinc(Zn)and Cd belong to the same family,the two elements have similar chemical properties.Although they have some interaction in plants,the specific effects and mechanisms have not been determined.Therefore,‘wuyun 24' was chosen as the rice cultivar to study the physiological effects of Cd stress and Zn under certain Cd stress on rice growth and the characteristics of translocation and accumulation of Cd in rice cultivars through hydroponic and pot culture experiments,and then examine the potential mechanisms of Cd and Zn interactions on rice.The main results were summarized as follows:1.The inhibitory effect of Cd on rice growth was more significant as the germination rate,plant height and chlorophyll value of rice decreased with the increase of Cd concentration.2.The malondialdehyde(MDA)content increased at a concentration range of 0-5mg/L,indicating the enhancement of lipid peroxidation.By contrast,the MDA content slightly decreased at concentrations higher than 5 mg/L.Peroxidase(POD)activity exhibited active response to oxidative stress at concentrations lower than 5 mg/L but was inhibited at concentrations higher than 5 mg/L.The positive response to Cd stress of proteins,carbohydrates and other organic substances with the N-H,O-H and C-O functional groups in rice shoots was observed via Fourier transform infrared spectroscopy(FTIR).3.The distribution characteristics of Cd in rice were in the following order: roots(29)stems(29)grains.The bioconcentration factor(BCF)values of Cd increased at 1 mg Cd/kg and approximately decreased to a constant value at concentrations higher than 1 mg Cd/kg.Rice showed a higher Cd accumulation potential at low Cd concentrations than high.The Freundlich isotherm model described well the adsorption isotherms of Cd in rice roots.The biosorption mechanism of rice roots was determined to be cooperative adsorption.4.The effects of Zn under certain Cd stress on the germination rate and root length of rice wasn't significant.However,plant height and chlorophyll value of rice were increased under 2 mg/L Zn treatment with respect to the control,which implied the alleviation effectof Zn on Cd toxicity.With the increasing concentrations of Zn,plant height and chlorophyll value were reduced significantly,indicating the enhancement of Cd toxicity to rice seedlings.5.The MDA content was decreased under Zn and certain Cd treatments,suggesting the mitigation of oxidative injury induced by Cd.Whereas,MDA content was increased significantly at high Zn concentration(20 mg/L),indicated that the oxidative damage generated by Cd stress was enhanced.It is observed that POD activity made no response to oxidative stress under Zn and certain Cd treatments,so the detoxification effect of Zn on Cd was not achieved by increasing the activity of POD enzyme.It is speculated that the metabolism of amino acids,carbohydrates and other substances in rice seedlings could be in positive response to Cd stress combined with the results of FTIR analysis.6.The Cd content and BCF in roots and stems of rice and translocation factors(TF)were increased at concentrations lower than 8 mg Zn/kg under certain Cd stress,and the synergistic effect was presented between Zn and Cd.However,the antagonistic effect was presented at 8 mg Zn/kg as the Cd content,BCF and TF in rice plants were decreased.Correlation analysis showed that there was no significant correlation between the contents of Zn and Cd in different parts of rice.The Cd content in rice grain was decreased and Zn content increased under Zn and certain Cd stress.The results of health risk assessment showed that the rice grain produced at 2 mg Zn/kg have no significant impact on human health.