Effects Of Cadmium,Lead Stress On Morphological Development And Physiological Metabolism And Research On Their Accumulation In Wheat

Heavy metal pollution is an important factor that limiting productivity of global wheat and threatening the ecological environment,and humans are exposed to them through various pathyways.In order to explore the toxic mechanism of heavy metal cadmium and lead on wheat,we studied the effects of different concentrations(10,20,40 mg·L^-1)of cadmium?Cd?on Zhongyu 10,Zhoumai 18,Luomai 23,as well as different concentrations(50,100,200mg·L^-1)of Lead?Pb?on Xinong 99,Jing 411,Jimai 22 about wheat seed development and physiological mechanisms,respectively,including catalase activity,soluble sugar content,soluble protein content,malondialdehyde content,proline content,root activity,net photosynthetic rate,intercellular CO₂ concentration,stomatal conductance and transpiration rate.The mechanisms of the accumulation of Cd and Pb were studied in eight wheat materials,respectively.The main objectives of the study was to analyze the dynamic respose of the above indicators,in order to provide theoretic background for growing wheat in ground contaminated with Cd and Pb.The following conclusions:The results of the research showed that with the increasing concentration of Cd,the germination rate,root length and upper root length of Zhongyu 10,Zhoumai 18 and Luomai23 were significantly lower than the control?P<0.05?.The germination rates of Zhongyu 10,Zhoumai 18,and Luomai 23 decreased by 12%,20%,and 42%,respectively,under the treat with 20 mg·L^-1 Cd.The growth of wheat was inhibited as the improve of Cd solution concentration.The root length of Zhongyu 10 decreased by 69%,and the root length of Luomai 23 decreased by 80%under 40 mg·L^-1 Cd stress.Besides,POD activity,SOD activity,CAT activity,soluble protein content,soluble sugar content,MDA content,proline content and intercellular CO₂ concentration all increased in flag leaves at seeding stage.Zhongyu 10 increased more than Luomai 23,and exhibited some adaptability.While root activity,net photosynthetic rate,transpiration rate,and stomatal conductance all decreased,and Luomai 23 decreased more than Zhongyu 10.Through the transmission electron microscopy,we analyzed the cell ultrastructure of wheat root.It was found that under the treatment of 20 mg·L^-1 Cd,the number of mitochondria increased,the shape became smaller,mitochondrial membrane was observed destroyed,mitochondrial crista ruptuing and appeared vacuole.The volume of the vacuole became large gradually.The surface of the cell membrane became rough and protrudes inward,forming uneven structure,and the ability to maintain permeability was gradually lost,so the Cd resistance of Zhongyu 10 was stronger than that of Zhoumai 18,and the Cd resistance of Zhoumai 18 was stronger than that of Luomai 23.The results showed that under the treat with 50 mg·L^-11 Pb,there was no significant difference between the germination rate,root length and upper root length of Jing 411 and Xinong 99 and the control?P>0.05?.Besides,the germination rate,root length and upper root length of the screened three cultivars decreased significantly?P<0.05?by Pb treatments.Furthermore,POD activity,SOD activity,CAT activity,soluble protein content,soluble sugar content,MDA content,proline content and intercellular CO₂ concentration all increased in flag leaves at seeding stage.While root activity,net photosynthetic rate,transpiration rate,and stomatal conductance all decreased,and Jimai 22 decreased more than Jing 411,so the Pb resistance of Jing 411 was stronger than that of Xinong 99,and the Pb resistance of Xinong 99was stronger than that of Jimai 22.The Cd content in wheat stalk varied from 0.002 to 0.354 mg·kg^-1 and in grains varied from 0.004 to 0.197 mg·kg^-1.The Cd accumulation of three wheat cultivars in the grain was less than in the stalk.The Cd content in the grains exceeded the limits set by the National Food Safety Standard in the Cd 20 mg·kg^-1 contaminated soil,which indicated that there was strong cadmium enrichment capacity for wheat.The translocation factor?TF?of three cultivars in each treatment was less than 1,that showed that the concentration of stalk was stronger than that of grain,so that the Cd resistance of wheat was improved to some extent.The Pb content in wheat stalk varied from 0.008 to 1.407 mg·kg^-1 and in grains varied from 0.001 to 0.209 mg·kg^-1.The Cd accumulation of three wheat cultivars in the grain was less than in the stalk.While the content of Pb was below 500 mg·kg^-11 in soil,the Pb content in the grain of wheat was higher than the National Food Safety Standard(0.2 mg·kg^-1).At higer concentration(1000 mg·kg^-1)of Pb,only was Pb accumulation in Chinese Spring grain higher than the National Food Safety Standard,indicating that the amount of accumulators for Pb by wheat was relatively small.