The Effect Of Arsenic Species On The Safety And Quality Of Lettuce

Arsenic(As)is a toxic metal commonly found in various environmental media and is a non-essential element in plants.Arsenic inhibits crop growth by affecting plant respiration,photosynthesis,nutrient metabolism,etc.Different forms of arsenic have different toxicity.Arsenic can be passed through the food chain and eventually affect human health.For a long time,domestic and international studies have focused on the accumulation of arsenic in seafood,while there have been fewer studies on the toxicity of arsenic in vegetables,most of which have focused on the comparison of enrichment coefficients and sensitivities between different species,while the effects of different forms of arsenic on plants are scarce,and there is a lack of systematic studies on the safe quality and metabolic mechanisms of arsenic stress on plants.In this study,we selected lettuce as research material,which is one of the most commonly consumed vegetables and has a high arsenic concentration.Hydroponics was used as a research method to explore the effects of different concentrations of different forms of arsenic on lettuce.The contents include the accumulation patterns of arsenic in different tissues of lettuce under different forms of arsenic stress;the effects of different forms of arsenic on the growth,nutrients and quality of lettuce;the effects of different forms of arsenic stress on the amino acid metabolites of lettuce.The specific findings are as follows:In the present study,arsenic stress studies were set up with different concentrations and different forms of arsenic,and the dynamic monitoring of arsenic forms in the culture solution was carried out.The results showed that the pH of the culture solution decreased with the increase of the added arsenic concentration,i.e.,the higher the concentration of As(?),As(?),the more severe the stress on lettuce and the more organic acids produced by the roots.Lettuce plants promoted the oxidation of As(?)in culture broth;As(?),As(?)stresses led to the presence of As(?)in lettuce roots,stems and leaves.When the initial As(?)concentration is less than 5 mg·L-~1 and the As(?)concentration is less than 2mg·L-~1 in the culture solution,the arsenic content in lettuce leaves will not exceed the arsenic limit for fresh vegetables in the"National Standard for Food Safety"(GB 2762-2017).We investigated the effects of different concentrations and morphologies of arsenic on the growth performance(fresh weight,plant height,root length,chlorophyll)and antioxidant enzyme system of lettuce.Studies have shown that low concentration of As(?)(?-0.5)can promote the growth of lettuce,and the fresh weight,plant height,root length and relative contents of chlorophyll of lettuce are all higher than those of CK treatment group.High concentration arsenic treatment group(?-10,?-2)significantly inhibited the growth of lettuce,stunted plants,and blocked root growth.Under the stress of As(?)and As(?),MDA and GSH contents in lettuce leaves were significantly increased.As(?)stress,SOD activity in lettuce leaves first increased and then decreased with As(?)concentration,CAT activity increased;As(?)stress,SOD activity in lettuce leaves increased,and CAT and POD activity decreased.The effects of different concentrations and forms of arsenic on nutrient elements(Ca,Mg,Mn,Fe,Cu,Zn)and quality indexes(vitamin C,total phenol,soluble sugar,nitrate)in lettuce were investigated.Low concentration of As(?)at 0.5 mg/L and low concentration of As(?)at 0.5 mg/L can promote the growth of lettuce,and significantly improve the quality of lettuce,significantly increase the content of vitamin C and soluble sugar,and reduce the content of nitrate.High concentration of As(?)at 10 mg/L and As(?)at 10 mg/L significantly inhibited the growth of lettuce,resulting in stunted lettuce plants and blocked root growth.Under As(?)stress,the total phenol content in lettuce leaves showed no significant change,while under As(?)stress,the total phenol content in lettuce leaves decreased significantly.Under the stress of As(?)and As(?),the content of Ca,Mg and Fe in lettuce leaves was significantly affected.Under the stress of high concentration of As(?)at 10 mg/L,the content of Mn,Cu and Zn in lettuce leaves in the middle growth and harvest period was significantly reduced,while As(?)had no significant influence on the content of Cu and Zn.The content of free amino acids in lettuce in different treatment groups was analyzed.The results showed that As(?)stress resulted in the down-regulation of most free amino acids in lettuce leaves,among which GLU(glutamic acid),ARG(arginine)and LEU(leucine)related to antioxidant system were the amino acids with greater influence under As(?)stress.The different amino acids under As(?)stress were histidine(HIS),arginine(ARG),glutamate(GLU),glycine(GLY)and leucine(LEU),which enhanced the chelating ability of lettuce to heavy metals.