Metabolomic Responses Of Rice Seedlings To Elevated CO₂ Concentration And/or Pb Stress

Heavy metal pollution of soils,as one of the major environmental problems facing the world,can lead to severe reduction of grain output and great direct economic loss,threatening the ecological system and human health.With the industrial development and human activities,the concentration of CO₂ is gradually increasing in the air.Therefore,the research on whether the high concentration of CO₂ can alleviate the toxic effect of heavy metals on crops can provide academic basis for the production practice of crop cultivation under the future change of air environment.In this research,rice were cultured with the CO₂concentration in the air?400±20?mol/mol?and the high concentration of CO₂?800±20?mol/mol?,and their physiological and metabolism responses to the low/high-concentration Pb stress?50?M,100?M?were researched.The experiment was divided into six treatment groups:control group?AC?,high-concentration CO₂ treatment group?EC?,different-concentration Pb stress group?L,H?,high-concentration CO₂ and Pb combined treatment group?EC+L,EC+H?.By determining the relative electric conductivity,MDA and antioxidant enzyme activities?SOD,POD,CAT?of rice seedlings,using the gas phase chromatography--mass spectrometry,combined with principal component analysis and partial least squares analysis,the change of metabolites in leaves of rice seedling were tested and analyzed,the effects of high concentration CO₂ and Pb stress and their combined effects on physiological metabolism of rice seedlings were discussed.The main research results include:1.Compared with AC.The relative electric conductivity of rice seedlings and the content of MDA increased significantly,SOD and CAT activities increased significantly,POD activity increased significantly in L treatment,but decreased significantly in H treatment through all the group of Pb stress treatment.A total of 18 metabolites were isolated from rice seedlings in L,including 8 amino acids,4 organic acids,4 sugars,2 other metabolites.A total of 21 metabolites were isolated from rice seeding in H,including 8amino acids,5 organic acids,5 sugars and organic alcohols,1 fatty acid,2 other metabolites.Pb stress promotes the accumulation of amino acids,sugars and organic acids in rice seedlings.The rice seedings cope with the damage caused by heavy metal Pb through enhanced glycolysis metabolism and TCA cycle.Meanwhile,it also can improve the activity of antioxidant enzymes and eliminate the active oxygen caused by Pb stress.2.The treatment under the high concentration of CO₂,compared with AC,the relative electric conductivity of rice seedlings decreased significantly,no significant change in the content of MDA,and SOD,POD,CAT activity increased significantly.A total of 18metabolites were isolated from rice seedlings under the high concentration of CO₂ treatment,including 5 amino acids,7 organic acids,3 sugars,1 fatty acid,2 other metabolites.High concentration of CO₂ can promote amino acid metabolism,carbohydrate accumulation and TCA cycle in rice seedlings.3.In the comparison of the Pb stress group?L,H?with the high concentration of CO₂and Pb compound treatment,the high concentration of CO₂ could alleviate the damage of cell membrane caused by Pb stress.The relative electric conductivity and the content of MDA decreased significantly in the rice seedlings.Scavenging reactive oxygen by increasing the activities of SOD,POD and CAT?Except for the change of SOD activity under EC+L treatment?.Through the perspective of metabonomics,the high concentration of CO₂ can not only provide nutrients for rice by the conversion of amino acids to sugars,but also form a complex and stable body combined with heavy metal ions through increasing the content of organic acids in plants.The enhancement of glycolysis and organic acid metabolism may relate to the resistance of Pb stress.