Effects Of Cadmium Stress On Metabolism Of Low Molecule Weight Organic Compounds In Root Exudates And Organs Of Eichhornia Crassipes

Water resources are vital to the survival of human beings,with the development of industry and human activities,heavy metal pollution in water is becoming increasingly serious.Researches have shown that the aquatic plant Eichhornia crassipes can effectively remove a large number of heavy metals in water which indicated that it has enormous potential in the remediation of heavy metal pollution.In this papper,Eichhornia crassipes seedlings were cultivated in a hydroponic system with 0,0.5,1,2,3 mg/L Cd treatment respectively.Sampling analysis was conducted at different exposure time(1 week,4 weeks,7 weeks)to investigate the changes of related physiological index(biomass,photosynthesis,Cd accumulation),low molecule weight organic compoubds(organic acids,amino acids,soluble sugars)in root exudation and different organs of Eichhornia crassipes.Finally,the effect of exogenous oxalic acid and glycine on Cd accumulation in Eichhornia crassipes was identified.The main conclusions were summarized as follows:1.Under Cd stress,the growth and development of Eichhornia crassipes was significantly inhibited reflected in reducing the biomass(mainly shoots)and weakening the photosynthesis.For the distribution of Cd in Eichhornia crassipes,the accumulation of Cd in roots was higher than that in shoots,but with the increase of Cd exposure concentration and the prolongation of exposure time,Eichhornia crassipes have the ability to transfer more Cd from the roots to the shoots.2.The addition of Cd significantly reduced the pH of the root exudates of Eichhornia crassipes,and the TOC and TN contents changed respectively.The results showed that oxalic acid and tartaric acid were dominated in the root exudates of Eichhornia crassipes.The addition of Cd promoted the secretion of these two acids during Cd exposure for 1 week,and reflected in the promotion at low Cd concentration and inhibition at high Cd concentration on the secretion of these two acids during Cd exposure for 4 weeks,while inhibited the secretion of these two acids during Cd exposure for 7 weeks.Oxalic acid,citric acid and malic acid were the main organic acids in the tissues of Eichhornia crassipes,and the content in shoots is higher than roots.During Cd stress for 1 week,Cd promoted the accumulation of citric acid and malic acid,inhibited the accumulation of oxalic acid in roots,while promoted the accumulation of oxalic acid and inhibited the accumulation of citric acid and malic acid in shoots.During Cd stress for 4 weeks,Cd inhibited the accumulation of oxalic acid and citric acid in roots,while promoted the accumulation of oxalic acid and inhibited the accumulation of citric acid in shoots.During Cd stress for 7 weeks,Cd affected the organic acids in the roots mainly in the accumulation of oxalic acid and malic acid,manifested as low concentration promotion,high concentration inhibition,while Cd promoted the accumulation of oxalic acid and inhibited the accumulation of citric acid and malic acid in shoots.Correlation analysis showed that there was a significant correlation between Cd contents and organic acids metabolism in Eichhornia crassipes.3.A total of 13 amino acids components were detected in the root exudates of Eichhornia crassipes.Glycine,alanine and serine were the three amino acids with high contents.The effect of Cd on the total amino acids exudation showed that Cd addtion promoted the secretion of root amino acids during Cd stress for 1 week,and had no significant effect on the secretion of amino acids during Cd stress for 4 weeks,while inhibited the secretion of root amino acids during Cd stress for 7 weeks.At Cd stress for 1 week and 4 weeks,14 amino acids were detected in Eichhornia crassipes,and Cd addtion had a greater effect on total amino acids in shoots than roots,the difference was that Cd promoted the accumulation of amino acids in shoots in 1 week,while inhibited the accumulation of amino acids in 4 weeks.At Cd stress for 7 weeks,only 12 amino acids were detected in Eichhornia crassipes,cysteine and phenylalanine were not detected,the effect of Cd on the total amount of amino acids mainly reflected in inhibiting the accumulation of amino acids in roots.Correlation analysis showed that there was a significant correlation between Cd contents and amino acids metabolism in Eichhornia crassipes.4.During Cd stress for 1 week,the contents of soluble sugars in root exudation of Eichhornia crassipes exhibited a trend of increasing first and then decreasing,while it showed a different tendency of decreasing first,then increasing and decreasing at last during Cd stress for 4 and 7 weeks.The addition of Cd promoted the accumulation of soluble sugars in the roots of Eichhornia crassipes,and had little effect on soluble sugars contents in shoots under Cd cultivation for 1 week.The addition of Cd resulted the decrease of soluble sugars contents in roots,and increased the contents of soluble sugars in shoots only at high Cd concentration(3 mg/L)under Cd cultivation for 4 weeks.The addition of Cd simultaneously promoted the accumulation of soluble sugars in roots and shoots.Correlation analysis showed that there was a significant correlation between Cd contents and soluble sugars metabolism in Eichhornia crassipes.5.The effect of exogenous oxalic acid and glycine on the accumulation of Cd in Eichhornia crassipes was mainly manifested in promoting the accumulation of Cd in roots,but the promotion of glycine is stronger than that of oxalic acid.