Mechanism Of Cadmium Accumulation In Different Genotype Tobacco

In this paper,two genotypes of tobacco K326 which cadmium accumulation in leaves and N.rustica which cadmium accumulation in roots were used as experimental material.Through the hydroponic system,to conduct a comparative study on Cd accumulation,Cd subcellular distribution,Cd speciation,root construction,submicroscopic structure of root and leaf,Photosynthesis and Carbon and nitrogen metabolism under cadmium Stress.The main findings are as follows:(1)Cadmium stress had no significant effect on the biomass of K326 and N.rustica,but it affected the distribution of biomass.Under cadmium Stress,The K326 allocates more biomass to the aerial part,while N.rustica distributes more biomass to the subsurface.There were significant differences in cadmium accumulation,The K326 accumulated more cadmium in leaves,while N.rustica accumulated more cadmium in roots.There were also differences in the root construction of the two,the root surface area and root tip number of K326 showed a decreasing trend,while the root surface area,average root diameter,root volume and root tip number of N.rustica showed an upward trend.From the point of view of transport factort of cadmium,the TF subsurface to aerial part of K326 is 17.34 times that of N.rustica,so there was a significant difference between the two groups in the transport ability of cadmium from the underground part to the aboveground part.(2)The Cd make the net photosynthetic rate of K326 and N.rustica significantly reduce,and the decline range of K326 is less than N.rustica,but the net photosynthetic rate of N.rustica is higher than that of K326.The decrease of net photosynthetic rate of N.rustica might be due to the decrease of stomatal conductance and the decrease of chlorophyll content,while the main reason for the decrease of net photosynthetic rate 76 of K326 was the decrease of stomatal conductance.(3)The sucrose synthase(SS)and sucrose phosphate synthase(SPS)activities in roots and leaves of K326 and N.rustica had no significant changes after cadmium treatment,howere,there were significant differences in distribution of sucrose and soluble sugar.The sugar in K326 was more assigned to leaves,while the sugar in N.rustica was more assigned to roots.The allocation model of sugar in K326 and N.rustica showed the same trend with their biomass allocation patterns(the biomass in K326 was more assigned to leaves,while the biomass in N.rustica was more assigned to roots).(4)After cadmium treatment,the nitrate reductase activity in roots and leaves of K326 and N.rustica both decreased.Under Cd stress,there was some difference between K326 and N.rustica in the detoxification of ammonium nitrogen.The Cd stress made the content of ammonium nitrogen in leaves of K326 and N.rustica significantly increased(increased by 96.14% and 41.59%,respectively).The content of ammonium nitrogen in roots also showed an upward trend,howener,the changes of ammonium nitrogen in K326 to a significant level,while that in N.rustica is not significantly different.It showed that the nitrogen metabolism activities in roots of N.rustica could be to meet its ammonium cycle detoxification,while the K326 was subject to a certain degree poisoning of ammonium.(5)After cadmium treatment,There was no difference in the Cd subcellular distribution in roots and leaves of K326 and N.rustica,they were both expressed as: soluble components of ribosomes> cell wall components> nuclear and chloroplast> mitochondrion.However,the ratio of cadmium subcellular distribution in leaves and roots of K326 and N.rustica was different: the roots accumulate more cadmiumin in the soluble fraction of the ribosome,which is called the vacuole,and the leaves were mainly accumulated in vacuoles and cell walls.These results were consistent with the i Intuitive positioning of the Cd subcellular distribution by TEM.(6)After cadmium treatment,there were differences in Cd speciation in roots and leaves of K326 and N.rustica.The presence of cadmium in leaves of K326 and N.rustica was mainly extracted by sodium chloride,deionized water and acetic acid,and that in leaves was mainly extracted by sodium chloride and ethanol.But in the K326 roots,the strong toxicity cadmium extracted by ethanol was the first;while in the N.rustica roots,the low toxicity cadmium extracted by sodium chloride was the first.It was showed that N.rustica roots can be better combine cadmium with pectate and protein,which reduced the toxicity of cadmium and weaken the mobility of cadmium,thus the toxic effect of cadmium on the ground was reduced.