| Lentinus edodes(L.edodes)is one of the most popular varieties of edible mushrooms because of its rich nutritional value and important edible and medicinal value.Cadmium is a heavy metal that exists in the environment,which can endanger human health through the food chain.Excessive cadmium entering the human body will do great harm to human immunity,liver and kidney,and serious will cause cancer.L.edodes has the characteristic of enriching cadmium,so there will be a high content of cadmium in L.edodes,which will affect the safety of food.Therefore,it is of great significance to study the control of cadmium by L.edodes and its mechanism.In this paper,a series of competitive adsorbents and microorganisms were added to the mycelium of L.edodes to observe the growth of mycelium,determine its oxidative stress,observe the microstructure of mycelium by scanning electron microscope,determine the content of cadmium and calcium in mycelium and culture medium by ICP-MS,and explore the control mechanism of cadmium in L.edodes mycelium under low cadmium stress at physiological and molecular level by transcriptome sequencing.To provide theoretical reference for controlling the content of cadmium in L.edodes.The main results are as follows:(1)Ca was used as a typical competitive adsorbent to study the effect of different concentrations of exogenous Ca on cadmium uptake by L.edodes mycelium.The results showed that the addition of different concentrations of exogenous Ca significantly promoted the absorption of Cd and Ca by mycelium under low cadmium stress,and the effect was the best when 20 mg/L Ca was added,which was contrary to the expected result of inhibiting Cd absorption,which may be due to the effect of Ca on oxidative stress in mycelium.(2)In the case of adding exogenous Ca,continue to add EGTA to explore the effect of Ca+EGTA treatment on cadmium uptake by L.edodes mycelium.The results showed that the co-treatment of different concentrations of exogenous Ca+EGTA significantly inhibited the absorption of Cd by hyphae and greatly promoted the absorption of Ca by hyphae under low cadmium stress.This inhibitory effect may be related to oxidative stress system.(3)By studying the expression of some genes related to Ca2+ transport(Ca M and Ca MK),)to explore the mechanism of Ca and Ca+EGTA treatment on the absorption of cadmium in L.edodes mycelium.The results showed that Ca and Ca+EGTA treatments of L.edodes mycelia under low cadmium stress could regulate the activities of Ca M and Ca MK.These two treatments decreased the expression of Ca M-related genes containing EF-hand domain,but both up-regulated and down-regulated expression of Ca MK-related genes.(4)The representative CK group,Cd treatment group,20 mg/L Ca treatment group and70 mg/L Ca+EGTA treatment group were selected to further explore the mechanism of the effect of other genes except Ca2+ transport on cadmium uptake in L.edodes mycelium by transcriptome sequencing.The results of transcriptome showed that there were 2392 differential genes in Cd treatment group,including 1346 up-regulated genes and 1046down-regulated genes,3214 differential genes in 20 mg/L Ca treatment group,including1661 up-regulated genes and 1553 down-regulated genes,and 775 differential genes in 70mg/L Ca+EGTA treatment group,including 354 up-regulated genes and 421down-regulated genes.The differential genes were annotated to the GO database for gene functional classification.The mycelia of L.edodes under different treatments responded to cadmium stress mainly through the difference of gene expression in transmembrane transport in the biological process.(5)To explore the effects of different microorganisms(Saccharomyces,Lactic acid bacteria,Bacillus subtilis,Bacillus stearothermophilus)on the control of cadmium in the mycelium of L.edodes.The results showed that in terms of growth,Saccharomyces could significantly promote the growth of mycelium of L.edodes,and the promoting effect was the best when the concentration was 2%.In terms of cadmium content,Bacillus stearothermophilus could significantly inhibit the absorption of cadmium by hyphae.The inhibitory effect was the best when the concentration was 5%. |
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