Effects Of Arsenic Compounds On Physiology,Biochemistry And Bioaccumulation Of Lettuce

With the continuous development of society,environmental problems have become more and more prominent,and environmental pollution has attracted widespread attention,such as heavy metal pollution.Heavy metal arsenic has become one of the main research objects due to its wide variety and great potential harm.In this paper,six arsenic compounds,heptahydrate and disodium hydrogen arsenate（As（Ⅴ））,sodium arsenite（As（Ⅲ））,asanic acid（p-ASA）,roxarsone（ROX）,sodium metharsate（MMA）and sodium dimethyl arsenate trihydrate（DMA）,were used for the hydroponic experiment of lettuce.The effects on biomass,photosynthesis（chlorophyll and nitrogen）,protein,malondialdehyde（MDA）,antioxidant enzymes（superoxide dismutase（SOD）and peroxidase（POD））,free radicals（superoxide anion radical（O₂^-）and hydrogen peroxide（H₂O₂））of lettuce were studied.The accumulation and morphology distribution of different arsenic compounds in lettuce were studied and the correlation analysis was made based on this.The main research results are as follows:（1）The physiological and biochemical effects of six arsenic compounds on lettuce were studied.The results showed that 5mM arsenic compounds could promote the yield of lettuce,and with the increase of As（Ⅲ）concentrations of the pollutant of opposite leaves yield the most significant effect,25m M As（Ⅲ）stress significantly inhibited the protein synthesis in lettuce on the 20th day,High concentrations of As（Ⅲ）,As（Ⅴ）,MMA,DMA,and ROX stress significantly inhibited the synthesis of chlorophyll and nitrogen in lettuce on the 20th day,and affected the normal photosynthesis of lettuce.The effects of six arsenic compounds on antioxidant enzymes in lettuce were not obvious.（2）The effects of six arsenic compounds on the accumulation and morphology distribution of arsenic in lettuce were studied.The results showed that with the increase of As（Ⅴ）,MMA,DMA,p-ASA and ROX concentrations,total arsenic in lettuce leaves gradually accumulated.The total arsenic accumulation in As（Ⅲ）,As（Ⅴ）,MMA,DMA,p-ASA and ROX leaves were0.52～1.85mg/g,0.15～3.57mg/g,1.50～10.11mg/g,0.43～1.09mg/g,0.37～5.24mg/g,and0.49～3.07mg/g respectively.When As（Ⅲ）and MMA concentrations exceeded 5mM,As（Ⅴ）,p-ASA and ROX concentrations exceeded 50mM,and DMA concentrations exceeded 10mM,arsenic content in lettuce leaves exceeded the national safety limit（0.5 mg/kg）.Studies showed that As（Ⅲ）,As（Ⅴ）,MMA,DMA,p-ASA and ROX could be absorbed by lettuce and migrated in vivo.（3）Pearson correlation analysis,principal component analysis and redundancy analysis were used in this paper to explore the influencing factors and mechanism of arsenic on lettuce physiology and biochemistry.According to the correlation analysis,different arsenic compounds have different effects on various physiological and biochemical indexes.According to the principal component analysis,the effects of arsenic compounds on the physiological and biochemical indexes of lettuce are mainly the fresh leaf weight,photosynthesis,protein,free radical and cell membrane plasmic structure of lettuce.Through the redundancy analysis,it is found that the effects of i-As,total arsenic and arsenic concentration on the physiological and biochemical indexes of lettuce are not significantly different.However,the comprehensive effects of arsenic compounds on physiological and biochemical characteristics of lettuce were significantly different.Its size is similar to that of MMA and As（Ⅲ）,followed by DMA,ROX,As（Ⅴ）and p-ASA.