Tolerance And Mechanism Of Daucus Carota To Manganese Stress

Daucus carota is a biennial herbaceous plant in the genus Daucus of the Umbelliferae family.It has the characteristics of large biomass,beautiful plant type,wide adaptability and strong stress resistance.Field investigations show that the plant has a large area distribution in the wasteland of manganese mines,and can bloom and produce normally,indicating that the plant has strong manganese tolerance and is a valuable material for phytoremediation of manganese pollution.Phenotypic adaptation,enrichment capacity,subcellular components,chemical morphology,physiological and biochemical adaptability and molecular mechanism of D.carota under manganese stress were studied by pot experiment.The results will clarify the physiological response mechanism of D.carota to manganese stress,explain the internal detoxification mechanism of D.carota tolerance to manganese stress and high manganese enrichment,and identify the key genes and regulatory pathways of manganese accumulation and detoxification in D.carota leaves.The results are as follows:(1)The germination experiment results showed that with the increase of manganese concentration,the germination energy,germination rate,germination index and vigor index of D.carota seeds all increased firstly and then decreased.(2)The results of pot experiment demonstrated that the biomass of both seedlings and adult plants of D.carota showed a trend of low promotion and high inhibition.On the 7,15 and 30 days of manganese stress,the root surface area,root volume,average root diameter,number of fibrous roots and leaf area of D.carota all increased first and then decreased with the increase of manganese concentration.With the extension of manganese treatment time,the specific leaf area of D.carotas decreased.On the 7th day of stress,the specific leaf area of D.carotas decreased with the increase of manganese concentration;on the 15th day of stress,the specific leaf area of D.carotas increased first and then decreased with the increase of manganese concentration;on the 30th day of stress,the specific leaf area of D.carotas increase with the increase of manganese concentration.(3)The results of pot experiment demonstrated that 1000?5000?M manganese treatment increased the chlorophyll a,chlorophyll b,carotenoid content and chlorophyll a+b content of D.carota seedling leaves;when the concentration continued to increase and the treatment time prolonged,each value decreased.With the increase of manganese concentration,on the 7th day of stress,the activities of SOD and CAT in carrot seedling leaves increased firstly and then decreased,and the activity of POD increased.On the 30th day of stress,SOD,POD and CAT increased first and then decreased.With the increase of manganese concentration,the content of proline and soluble protein in D.carota seedling leaves showed a trend of first increasing and then decreasing on the 7,15,and 30 days.The soluble sugar content increased with the increase of manganese concentration on the 7th day,and then increased first and then decreased with the increase of manganese concentration on the 15th and 30th day.The content of malondialdehyde(MDA)increases with the increase of manganese concentration and the extension of stress time.(4)The results of leaf anatomical structure showed that the thickness of main vein,upper epidermis and lower epidermis of D.carota leaves increased first and then decreased with the increase of Mn concentration,while leaf thickness showed a downward trend.The thickness of D.carota fence tissue,the thickness of sponge tissue and the tightness of tissue structure all showed a trend of first increasing and then decreasing with the increase of manganese stress concentration.(5)With the increase of manganese concentration,the manganese content in both aboveground and underground parts of D.carota increased.Under the treatment of 20000 ?M manganese solution,the manganese content in the aboveground and underground parts of D.carota reached 16948.37 mg·kg-1 and 13210.33 mg·kg-1,respectively.BCF and TF of D.carota were more than 1.Manganese content in cell wall component and soluble component of D.carota was the highest.Manganese in D.carota mainly exists in ethanol extract,deionized water extract and sodium chloride extract.(6)RNA-Seq transcriptome sequencing was tested on D.carota plants with or without manganese stress,and 15,938,788,680 bp gene data of the transcriptome were obtained.Compared with the control group,there are 4047 genes differentially expressed in D.carota with manganese stress,among which 2128 genes were up-regulated.This study filtered and identified 26 antioxidant defense differential genes,12 encoding metal transporters genes,and initially constructed a gene network for manganese defense and detoxification of D.carota,which provided a foundation for further revealing the molecular mechanism of plant manganese accumulation and detoxification.This study showed that D.carota can reduce the damage caused by high manganese stress by increasing the concentration of osmotic regulating substances and enhancing the activity of antioxidant enzymes,and store most of manganese in cell walls and vacuoles to improve manganese tolerance.