Effects Of Malic Acid On The Uptake And Translocation Of Cadmium In Rice

Pollution caused by heavy metal cadmium in rice and farmland of China is becoming a serious problem.Malic acid is a kind of organic acid with small molecule which is involved in a variety of metabolic processes in plant organelles.It plays an important role in plant growth regulation and toxic metal tolerance.In this paper,several rice genotypes were used as experiment materials.Based on the results from hydroponic culture,detached leaf test and foliar application with malic acid,effects of malic acid on the accumulation of cadmium in rice were analyzed.Results from this study may provide a reference for developing the foliar conditioner.The main conclusions are as follows:?1?Genotypes and malic acid have significant effects on the content of Cd,K,Ca,Fe,Mn and Zn in roots and shoots of rice seedlings.X24 is a low cadmium accumulation genotype.No.20,No.58 and No.65 are high cadmium accumulation genotypes.Experimental results showed that 0.5¹.5 mmol·L^-1malic acid significantly reduced the Cd concentration in roots and shoots of rice seedlings.The maximum reduction of cadmium content was achieved when the concentration of malic acid was raised to 1.5 mmol·L^-1.In the absence of cadmium,accumulation of the essential elements in roots and shoots of rice seedlings from different genotypes were obviously different.The effect of cadmium on the accumulation of essential elements in rice seedlings of different genotypes was also different.Cadmium inhibited the absorption of essential nutrients in rice seedlings.Adding 0.5 mmol·L^-1 and 1.5 mmol·L^-1malic acid can reduce the accumulation of K,Fe and Zn in roots of rice seedlings,and promote the accumulation of Ca in roots.Malic acid has smaller influence on the accumulation of essential elements in shoots than that in roots of rice seedling.?2?Malic acid can significantly alleviate the toxicity of cadmium to root development.0.3mg·L^-1cadmium reduced the root length,root surface area,root volume,root tip number of seedlings from high-Cd-accumulating genotype?No.58?by 45.8%,19.8%,6.2%and 26.4%,respectively.Adding 1.5mmol·L^-1 malic acid in hydroponic liquid can alleviate the toxicity of 0.3 mg·L^-11 cadmium in rice.1.5mmol·L^-1 malic acid can significantly increase the root length and root tip of seedlings from No.58genotype by 42.8%and 57.8%,respectively.The peroper concentration of malic acid has a positive effect on the growth and development of rice seedlings.?3?Genotype and malic acid have significant effects on the Cd accumulation and total chlorophyll of detached leaves.Under 1.0 mg·L^-1 cadmium stress,the accumulation of cadmium in detached leaves was significantly different among genotypes.No.43 is a low cadmium accumulation genotype and No.58 is a high cadmium accumulation genotype.0.1¹.5 mmol·L^-11 malic acid can significantly inhibite the accumulation of cadmium in detached leaves,and inhibition effect depends on genotypes.No.9genotype is more sensitive to malic acid than others.Cadmium can promote the chlorosis rate of chlorophyll in detached leaves.Adding malic acid can alleviate the damage of cadmium to chlorophyll.?4?Spraying malic acid and manganese and zinc can effectively inhibit the transfer of Cd between rice organs,significantly reduce the Cd content in rice.Experimental results show that 10 mmol·L^-1MnCl₂,10 mmol·L^-11 ZnCl₂,5 mmol·L^-11 malic acid can significantly reduce the Cd concentration in grains,rachises,uppermost internodes and flag leaves of rice plants.Cd concentration in grains decreased from 0.63 mg·kg^-1 to 0.47,0.28 and 0.26 mg·kg^-1,and thecorresponding Cd falling percentage was 23.84%,55.44%and 58.86%,respectively.Malic acid can also significantly reduce Mn content in each organ.Malic acid and Mn²⁺and Zn²⁺promote the transfer of Mg,K,Mn and Fe from flag leaves to uppermost internodes.