Mechanisms Of Organic Selenium Accumulating In Peanut Seedlings And The Bioactivities Of Organic Selenium

Selenium is one of the essential trace elements in human body,it has many bioactive functions.The diseases caused by insufficiency of selenium pose a major threat to human health.It had been proved that adequate supplementation of selenium can improve immunity and prevent many diseases.However,because of the cytotoxicity of inorganic selenium,the organic selenium obtained through biological enrichment is an important source for people and animals to supplement selenium.In order to obtain the selenium-rich peanut sprouts,peanut seedlings were growing in an inorganic selenium（sodium selenite）medium.The formation of organic selenium through the process of seedlings growing was studied.Also,the effects of selenite on the antioxidant defense system and the mechanisms of selenite for the regulation of the phenylpropanoid pathway in peanut seedlings were investigated.Moreover,the bioactivities of organic selenium and inorganic selenium were investigated using human erythrocytes and mice macrophages RAW 264.7 cells.The results were as follows:Selenite treatments up-regulated the Cu Zn-SOD gene expression and increased its activity.Concurrently,selenite treatments resulted in a rapid accumulation of hydrogen peroxide in the early stage of seedling growth,which may be a signal molecule involved in the regulation of antioxidant enzyme gene expressions.Selenite treatments increased the GSH-Px,GST,and APX enzyme activities and enhanced the concentration of nonenzymatic antioxidants such as GSH and AsA,probably by mediating the ascorbate-glutathione cycle,thus decrease in H₂O₂accumulation and MDA formation in peanut seedlings and subsequently increasing the free radical scavenging activity.The enhance of anti-oxidant capacity of peanut seedlings may be one of the mechanisms which to the benefit of selenium accumulated in peanut seedlings.Selenite up-regulated the relative genes expression and enzyme activities,and at last enhanced the phenylpropanoids,including bound phenolic acids,lignin,and total flavonoids,during peanut seedling development.The increased generation of these phenylpropanoid compounds enhanced the antioxidant capacity and stabilized and strengthened the cell structure,thus contributing to the alleviation of selenite-induced toxicity.Furthermore,selenite enhanced the formation of endodermis in roots,which may be attributed to the up-regulation of lignin biosynthesis mediated by H₂O₂ and NO,which probably regulated the selenite uptake from an external medium.Peanut seedlings were growing by using quartz sand as the culture medium and irrigated with different concentrations of sodium selenite water solution（0,3,6,and 10 mg/L）.The results showed that organic selenium was accumulated in the different parts of the peanut seedlings.Because of the different ability of accumulation of selenium,the concentration of organic selenium in root and hypocotyl were higher than that in cotyledon of peanut seedlings.On the 6^th day after grew with selenite,the most effective conversion rate of inorganic selenium to organic selenium in peanut seedlings was found with the treatment of 6 mg/L selenite.Seleno amino acids were the main form of organic selenium in selenium-rich plant,and it was speculated that selenite treatment increases the synthesis of seleno amino acids in peanut seedlings.There was similar structure between selenocystine and cystine,L-Se-methylselenocysteine and cysteine,selenomethionine and methionine.The only difference between these three group of amino acids was the containing of selenium or not.The bioactivity results showed that seleno amino acids had strong protective effects on human erythrocytes when under the AAPH oxidant stress.Whereas the non-seleno amino acids had no protective effect or lower protective effect on human erythrocytes.Further research on the enzymic and nonenzymic resistance system found that,seleno amino acids treatment significantly enhanced GSH concentration and GSH-Px and SOD activities.Seleno amino acids also normalized morphological features and reduced the MDA production.Nevertheless,the inorganic selenium and non-seleno amino acids couldn’t enhance the anti-oxidant capacity of human erythrocytes.These results demonstrated that seleno amino acids could be absorbed and utilized by human erythrocytes to enhance the anti-oxidant ability,while inorganic selenium could not be used to enhanced the anti-oxidant capacity on human erythrocytes.L-Se-methylselenocysteine had strong immune regulation activity in the mouse macrophage,RAW264.7 cells.L-Se-methylselenocysteine treatment promoted the immune response in RAW264.7 cells.Contradictorily,in the LPS-induce inflammation macrophage RAW 264.7 model,L-Se-methylselenocysteine showed a strong immunosuppressive effect.L-Se-methylselenocysteine inhibited the activation of the macrophage RAW 264.7 which induced by LPS.It also reduced the allergic reaction of RAW 264.7 cells,and keeped the morphology of macrophages normal.In addition,L-Se-methylselenocysteine treatment significantly reduced the secretion of the inflammation factors such as NO,TNF-alpha,IL-6 and IL-12.Eventually,L-Se-methylselenocysteine reduced the inflammation medium such as the expression of cox-2 and PGE2,thereby reducing the body’s inflammatory response.This study shown that organic selenium had a strong bioactive function in human and animal cells.It was very effective for increase the anti-oxidative activity and adjusted the immune response in human and animal cells.Peanut seedlings treatment with selenite was an effective method to enrich organic selenium.The mechanism of selenium accumulation was closely related to the antioxidant system of peanut seedlings and the secondary metabolism induced by selenite.This study provides a theoretical basis for the selenium enrichment and the development of organic selenium with bioactive function.Selenium enrichment in peanut seedlings has a broad application prospect in the development of selenium enrichment and functional foods.