Physiological Response And Transcriptome Analysis Of Cichorium Endivia L Seedlings Under Cadmium Stress

Cichorium endivia L is a biennial herb of Asteraceae,also known as Ruccola salad.As the actual situation of soil heavy metal pollution in China is getting more and more serious,combined with the current development trend of hydroponic vegetables.In this experiment,under the artificial light supplement environment of the plant factory,cadmium chloride was added by hydroponic method to control the concentration of heavy metal ions in the nutrient solution to explore the mechanism of cadmium stress in the seedlings of Momordica charantia.The following conclusions were drawn through the experiment:1.With the increase of cadmium ion concentration,the changes of plant height and fresh weight of above-ground parts of Cichorium endivia L seedlings showed a trend of inhibition,and the average plant height and fresh weight of above-ground parts gradually decreased.The seedlings of Cichorium endivia L showed weak resistance under cadmium stress.In the treatment of adding 10 mg / L of cadmium chloride solution in the hydroponic nutrient solution,the total cadmium accumulation in 3d exceeded national food safety standards It shows that bitter chicory has a strong ability to accumulate cadmium;however,as the accumulation of cadmium increases,the mortality rate of the plant also increases,and the ability to remove toxic heavy metals is weak.2.The ultramicroscopic structure of the leaves of Cichorium endivia L seedlings showed that the seedlings grown in the blank treatment CK had narrow,long and flat morphology,the inner and outer membrane structures were intact,evenly distributed along the cell membrane,and the structural function was normal.After adding the nutrient solution containing cadmium chloride,affected by cadmium ions,the distribution of chloroplasts no longer evenly follows the cell membrane,and a partial aggregation phenomenon occurs in the cytoplasm,and the chloroplast morphology undergoes different degrees of swelling.The base sheet breaks,and the arrangement and distribution become chaotic.Starch granules appear inside the chloroplast,the number gradually increases and the volume gradually increases.There was swelling or twisting between the thylakoid bodies,and some of the thylakoid bodies were blurred.Normal chloroplast function is obviously affected.3.The osmotic adjustment of Cichorium endivia L seedlings shows sensitivity to cadmium ions.With the increase of cadmium ion concentration,the contents of malondialdehyde and free proline both showed a trend of increasing first and then decreasing.When the concentration of cadmium ion reaches 0.5mg / L,the contents of malondialdehyde and free proline reach the maximum.When the concentration of cadmium ions added in the nutrient solution reached 1mg / L,the degree of stress began to exceed the limit of the plant’s own regulation effect,both osmotic adjustment substances were affected,the content began to decline,and the change trend was similar,but the malondialdehyde and free The content of proline is still higher than that of the blank control.The effect of plant osmotic adjustment to reduce the toxicity of heavy metal ions always exists.4.The experimental results show that SOD,POD and other antioxidant enzymes play no significant role in removing reactive oxygen radicals produced in the Cichorium endivia L seedlings under cadmium stress.The activity of SOD enzyme gradually decreased with the increase of the total cadmium content in the Cichorium endivia L seedlings,and the regulation and control of the generation and scavenging of active oxygen and free radicals also gradually decreased,and the ability to alleviate the damage of the plants to heavy metal stress was reduced.The POD enzyme decreased first and then increased.When the nutrient solution added cadmium ion concentration reached 1mg / L,the POD enzyme activity was the lowest;when the nutrient solution added cadmium ion concentration reached 10 mg / L,the POD enzyme activity was the highest.In the enzyme protection system,some enzyme activities are inhibited by heavy metal ions.Plants self-regulate and strengthen other enzyme activities,which generally leads to increased peroxidation of the membrane,which has a serious impact on the normal growth of the plant.5.With the increase of the concentration of cadmium ions added in the nutrient solution,the chlorophyll content of the Cichorium endivia L seedlings increased first and then decreased.When the concentration of cadmium ions added in the nutrient solution reached 5 mg / L,the chlorophyll content in the Cichorium endivia L seedlings reached the maximum value.With the increase of the total cadmium content in the plant,the degree of stress gradually exceeded the speed limit of chlorophyll synthesis,the chloroplast was affected and deformed,the photosynthesis of chlorophyll was inhibited,and the carotenoid gradually increased with the increase of cadmium accumulation in the body Co-factors,when chlorophyll is gradually inhibited,play a role in scavenging free radicals in plants and preventing membrane lipid peroxidation,ensuring the photosynthesis of plants.6.With reference to the full-length transcriptome sequence of the leaves of Cichorium endivia L seedlings,analysis of the leaf transcriptome expression profile yielded an average of 43.94 million reads,and the low-quality sequences were filtered and removed,and the number of remaining clean reads averaged about 40.38 million.The total number of sequencing nucleotides of all analyzed samples was above 6.0G.Under the stress of 10mg/L cadmium chloride treatment,a total of 2192 genes were differentially expressed,with the most active physiological metabolism,which was the most differentially expressed gene in each treatment group.GO entries of fructosyltransferase activity,sucrose 1F-fructosyltransferase activity,membrane-related cell components,oxidoreductase activity,etc.are significantly enriched.7.According to the experimental results,through the analysis of KEGG metabolic pathways,it was found that cadmium stress mainly affected the metabolic pathways of Cichorium endivia L seedlings: plant hormone signal transduction,starch and sucrose metabolism,galactose metabolism,sesquiterpene and triterpene biosynthesis,phenylpropane bio Five categories of synthesis.Mainly focus on the regulation of auxin,cytokinin and other plant hormones,maintain the plant physiological activities through the regulation of sugar metabolism,plant disease resistance and cell wall components and functional regulation,through the relevant metabolism of these pathways to affect or alleviate heavy metal ion bands Coming damage.