Responses Of Maize Seedlings To Cadmium Stresses And Mitigation Effects Of Silicon On Cadmium Toxicity

With the development of economic life,heavy metal cadmium?Cd?pollution caused by metallurgical,chemical fertilizers and chemical industries has been a serious threat to food safety and human health.In recent years,phytoremediation technology matures,toxic effect of heavy metals in plants has become a hot problem in the study on ecology and environmental protection,but the most studies in the field of contaminated soil as the medium simulation environment,cannot be ruled out the interference of other factors on exploration the mechanisms of Cd stresses.In this paper,responses of maize?Zea mays L.?seedlings under different concentrations of UdCl2 stress cultured with hydroponic system,Cd²⁺ deposit location in the maize root,and mitigation effects of Si on Cd toxicity by adding Na2SiO3,were studied and the results were as below:1)The effects of different concentration of Cd²⁺?0,10,20,40 mg·L-1?on maize seedlings found that low concentration of cadmium treatment?10 mg·L-1?had no significant inhibition of maize seedlings.The biomass slightly decreased,and the resistance of seedling was stimulated.The deepening greencolor of leaves enhanced photosynthesis,and the coarsen root diameter 'improved root rot situation.Cd concentrations were higher in the ground parts and root,thus transfer factor?TF?and enrichment coefficient?BC?were also the highest?0.62 and 104.01?,which was advantageous to accumulate Cd to corn seedlings.With the increasing of cadmium concentration to 20 mg·L-1 and 40 mg·L-1,the growth of seedlings was significantly suppressed,which including significant decrease of biomass,yellow and dry leaf thick and short rootswith yellowish-brown color,and even death of some seedlings.At these stress levels,although Cd concentrations in roots and aboveground parts were very high,the transfer coefficient?TF?and enrichment coefficients?BC?were decreased to 0.51 and 43.93.The results indicated that the conduction and absorption of Cd from root to the ground had been inhibited under high Cd stresses.Furthermore,maize seedlings could not grow again for such serious pollution.2)The observation of cadimium depositon by cutting thin slices?cross-section?from the tip of maize root showed that Cd²⁺ were mainly moved through apoplastic pathway into the root.A large number of Cd²⁺ accumulations were observedin the epidermal layer and outer layer,and outer cortex casparian strip would block most Cd²⁺ and prevent them into the central cortex.Otherwise,parts of Cdua defected out cortex cells could be transferred into the cortex by symplast pathway.Most Cd²⁺transferred through central cortex had been adhered to the cell wall or compartmented into vacuoles.And other Cd²⁺ had been transferred through column in the xylem and phloem to the ground eventually by endodermis casparian strip.3)The mitigation effects through addition of Na2SiO3?130 mg·L-1?to hydroponic system treated with high CdCl2?20 mg·L-1?.The results showed that exogenous Si significantly increased biomass,leaf and lateral root number of maize seedlings.Compared to the control,the shoot length,fresh weight and dry weight under Si treatment were 68.8%,57.1%and 75.3%respectively.The leaf number increased from 2.13 to 3.00,and lateral root number increased from 3.13 to 6.33.The transfer coefficient?TF?decreased from 0.96 to 0.79,and enrichment coefficient?BC?decreased from 67.91 to 45.93.The results indicated that Si could hinder the uptake of Cd²⁺ in root and transport Cd²⁺ to the ground.Therefore,combined Si and Cdtreatment may effectively alleviate the damage of Cd of maize seedlings through enhancement the photosynthesis and improvement the condition of nutrients and moisture absorption.It is applicable to plant maize in the presence of Si in the field with high concentration of Cd.