Study On The Mechanisms Of Polycyclic Aromatic Hydrocarbons Absorption And Stress Response For Chinese Flowering Cabbage

Polycyclic aromatic hydrocarbons(PAHs)are toxic organic pollutants that it exists widely in the environment for a long time.It can be absorbed and accumulated in plants by means of atmospheric sedimentation and sewage irrigation etcetera,which poses a great threat to agricultural products quality and human health.In this paper,PAHs and Chinese flowering cabbage were test materials,the regularities of different types PAHs absorption and accumulation,the effects on volatile and bioavailable content of different types PAHs by using microbial fertilizer and biomass carbon,the effects of PAHs absorption and accumulation for Chinese flowering cabbage,and the.mechanism of physiological response and molecular response of PAHs stress for Chinese flowering cabbage were studied.The main research results were as follows:1.The Chinese flowering cabbage was potted by using the contaminated soil of different PAHs concentrations,which studied on the regularities of different types PAHs absorption and accumulation for Chinese flowering cabbage.The results showed that the content of PAHs in roots,stems and leaves of Chinese flowering cabbage increased with the increasing of PAHs concentrations.The order of PAHs concentrations in different parts of Chinese flowering cabbage was roots>leaves>stems.The content of PAHs in leaves increased rapidly in 17 days after planting,17 days to 24 days,the rising speed slowed down.Low ring PAHs in Chinese flowering cabbage accounted for 77.61 to 90.3%of the total PAHs content,high ring PAHs accounted for 9.70%to 22.39%.The enrichment capacity of five kinds PAHs in soil for Chinese flowering cabbage was Phe>Nap>Flt>BaP>InP,the enrichment capacity of BaP and InP in roots was much greater than stems and leaves.After planting,the total contents of extractable PAHs in soils of each treatment were decreased in different degree,and the content of PAHs in the non-rhizosphere decreased from 22.92%to 27.98%than which before planting,the content of PAHs in rhizosphere soil was significantly lower than which in non-rhizosphere soil.2.The total content of extractable PAHs in soils was decreased significantly when microbial fertilizer and biomass carbon were added to soil,and the PAHs absorption from soil of Chinese flowering cabbage could be inhibited effectively.With the increasing of incubation time,the total content of extractable PAHs in soils showed a decreasing trend.The volatilization of Nap and Phe was inhibited significantly by using biomass carbon,in the same concentration,the effects of decreasing volatilization of Nap,Phe and Flt in soil by using biomass carbon were better than microbial fertilizer.The effects of decreasing volatilization of Flt in soil were not obvious by using biomass carbon and microbial fertilizer.Volatile quantities of Nap,Phe and Flt in soil gradually decreased with the increasing of incubation time.The bioavailability of PAHs in soil decreased by using biomass carbon in a short time,and the time of microbial fertilizer was longer than biomass carbon.With the increasing of incubation time,the effects of decreasing bioavailability of Nap and Phe were gradually increased by using microbial fertilizer,the bioavailability of Flt did not decrease significantly with the increasing of biomass carbon and microbial fertilizer in soil.The content of PAHs in aboveground parts and underground parts for Chinese flowering cabbage decreased with the increasing of biomass carbon and microbial fertilizer.3.The Chinese flowering cabbage was stressed by using the mixed solution of Nap,Phe,Flt,BaP and InP in soil,the effects of PAHs physiological toxicity were discussed.The results showed that the low concentration of PAHs stress could promote the growth of Chinese flowering cabbage,and the high concentration of PAHs stress could inhibit the normal growth of Chinese flowering cabbage.It showed that the stem diameter decreased,plant fresh weight and roots fresh weight decreased and bloom earlier.The content of MDA,H2O2 and pro line of Chinese flowering cabbage leaves increased with the time and concentration increased of PAHs stress.The content of soluble protein in leaves increased by low concentration PAHs stress,and it decreased by high concentration PAHs stress.The antioxidant protective enzymes activity of SOD,POD,CAT and APX was different by PAHs stress.The activity of SOD increased with the increasing of stress concentration.The activity of POD,CAT and APX increased firstly and then decreased with the increasing of stress concentration.With the increasing of stress time,the activity of SOD and POD increased gradually,and the activity of CAT and APX increased firstly and then decreased.4.The differentially expressed genes in leaves of Chinese flowering cabbage responsed to PAHs were analyzed by RNA-Seq.The number of raw reads obtained from 6 libraries was 29.46M,32.15M,40.78M,56.53M,46.42M and 39.53M.The percentage of clean reads from each library was more than 98%,and 73.8Gb data were obtained,the proportion of Q20 was more than 97.38%,and the proportion of Q30 was more than 93.63%,the GC content between 47.28%?48.63%,it remained stable between samples.The total number of known genes in all the samples was 32917,of which 1814 genes were new.The 1450 genes with significantly different expression were screened,689 genes of which were significantly up-regulated,and 761 genes were significantly downregulated.Through related bioinformatics analysis,117 transcription factors were identified from differentially expressed genes.In which,the genes expression of transcription factors family such as WRKY,MYB AP2/ERF and NAC were significantly changed in response to PAHs,the ethylene metabolic pathway genes expressed largely.In addition,40 genes involved in the synthesis of hormone and signal transduction were obtained.