| Vegetables are the necessities of human life.With the rapid development of agricultural economy,China has become the largest country in vegetable production and consumption in the world.In recent years,the heavy metal content exceeding the standard in soil has severely affected the safety of vegetable production and people's health,which due to the acceleration of urbanization and industrialization.Therefore,the study on the heavy metal pollution of the vegetable,and the key technologies of the prevention and remediation have become increasingly important.Nowadays,the vegetable field pollution caused by heavy metals mainly includes cadmium(Cd),lead(Pb),copper(Cu),arsenic(As)and other elements.The Cd,which belongs to the category ? carcinogen,is the primary resource in the heavy metal pollution in the vegetable field,and the national exceeding standard rate of points reached 7.0%.Compared with other heavy metals,it is easier absorptive.The Cd excessive accumulation in plants will seriously damage the chloroplast in the cells,reduce the chlorophyll content,interrupt the growth and development of vegetables,and eventually lead to a substantial declination in the vegetable eating quality.Like other heavy metals,there are many characteristics of the Cd,such as hidden,long-term and irreversible,which effects on the vegetables and the human body.The excessive Cd in vegetables can enter the human body through the food chain,and seriously harm the human body's health.Therefore,the research on the crucial technologies of the prevention and remediation of the vegetable heavy metal pollution should focus on the heavy metal Cd primarily.At present,there are many kinds of vegetables for producing and consuming.It is necessary to choose one vegetable to focus on the research.Previous studies have shown that leafy vegetables were easier contaminated by Cd than other vegetables,and thus the leafy vegetables are the first choice for the research.Chinese cabbage originated from China,is the most widely distributed vegetable crop with the largest field in China.The safety of the crop plays a vital role in people's lives.It is of considerable significance to study the theory and technology of the prevention and the remediation of heavy metal pollution by taking Chinese cabbage as a starting point.By the above background,our experiments selected the Chinese cabbage as the object and carried out the study on the molecular mechanism of Chinese cabbage's response to Cd stress.It will fully reveal the main regulation mechanism of leaf vegetables in response to heavy metal cadmium(Cd)stress and its application in vegetable field restoration.In this experiment,GDZ,a precocious cultivar with durable disease resistance,was first selected and cultured at concentrations of 0,25,50 and 100 ?M Cd Cl2 for 16 d to determine the differential association between transcriptome,from which the metabolic pathways and response genes were analyzed.For exploring the cultivars with low(high)-Cd accumulation and absorption,Atomic absorption spectrophotometry and the Noninvasive Microtest Technology(NMT)were carried out using 26 cultivars to analyze characteristics of the accumulation and the absorption.The main results are as follows:1.GDZ was analyzed after treatment,and it was observed that the growth statuses of the seedlings were different significantly.With the increase of the Cd concentration,the growth inhibition phenomenon became more and more apparent(the leaves became smaller,the color became yellow,and the root length become short),and the accumulation of Cd increased linearly in the body.2.Transcriptome sequence(RNA-Seq)was used to sequence each Chinese cabbage with each treatment,and the results showed that 889,1613,and 3863 differentially expressed genes were identified under 25,50,and 100 Cd Cl2 conditions,respectively,which compared with the leaves of Chinese cabbage seedlings in the control group.Comparing with the GO database,the results showed that 4,14 and 22 subcategories were significantly annotated.Through EGG pathway analysis,it was found that there were 92,95 and 115 pathways enriched respectively,indicating that Cd stress could seriously affect the growth and development of plants.3.KEGG(Kyoto Encyclopedia of Genes and Genomes)showed that Bra05g004360.3c,as one of the members of the glycosylase family,plays a crucial role in the whole biological process.The concentration of Cd may associate with the expression level of the gene,which encodes glycolytic hydrolase.Specifically,as the concentration of Cd increased,the expression level of Bra05g004360.3c decreased,which inhibits the synthesis of lignin in the cell wall,resulting in the reduction of lignin content and eventually leads to the poisoning of Chinese cabbage.4.Bra A04g026280.3c as a similar gene for coding RBR(Retinoblastoma-Related)protein,may combine with E2 F factors to play a role of repression,inhibition of the cell differentiation and the gene expression,reduce the cell cycle,and eventually lead to the growth restriction of the Chinese cabbage.5.For finding the Chinese cabbages in the leaves with higher and lower Cd content,we measured Cd content using 26 cultivars and measured the ability to absorb Cd in the roots,using selected "ZBX" with high-Cd accumulation(absorption)and "JL-75" with low accumulation(absorption).The study showed that during the absorption process,the rate did not always increase with the time creasing,and the flow rate would not change when it reached a specific time point.Different cultivars had different stable time points;In addition,the gene expression trends of Bra A05g004360.3C and Bra A04g026280.3C in "ZBX" and "JL-75" were the same as "GDZ".Therefore,Bra A05g004360.3C and Bra A04g026280.3C are the key genes of Cd tolerance mechanism,and their expression levels can affect the permeability of the cell wall to absorb Cd and the ability of cell division.Secondly,there are also differences in the efflux mechanism of plants,resulting in ccumulation differences among different cultivars.In conclusion,Cd concentration could be associated with the expression level of genes encoding glycosylase and RBR protein,which affected the metabolic process of Chinese cabbage and ultimately inhibited the growth and development of plants for responding to Cadmium Stress.At the same time,the absorption and accumulation characteristics of the different cultivars were significantly different under the same Cd concentration.According to the above mechanism,Chinese cabbages in the leaves with higher and lower Cd content(absorption)were selected for soil remediation and food safety respectively,which is of great significance to further explore the molecular mechanism of the response of Chinese cabbage to Cd stress. |
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