| Polycyclic aromatic hydrocarbons(PAHs),a class of persistent organic pollutants with strong teratogenicity,carcinogenicity and mutagenicity,are widely distributed in water,soil and other environments,and can contaminate food chain and endanger human health through the soil-based plant system.Therefore,the pollution and control of PAHs in the food chain has attracted a strong concern.However,the distribution of PAHs in different organs of crops at different growth stages and the effects of its control on crops at different growth stages have not been clear.In this paper,the dynamic accumulation of PAHs in different parts of wheat at different growth stages was investigated to study the translocation of root to stem,leaf,seed and leaf to grain.The changes of proteins in castor xylem sap were analyzed and the concentrations of naphthalene,phenanthrene and pyrene in various parts of wheat were determined on the basis of the application of biochar to investigate the effect of biochar on the absorption and migration of PAHs in wheat.The purpose of this study is to reveal the accumulation of PAHs in crops at different stages and the control effect of biochar to provide scientific basis and technical strategies for the guarantee of agricultural product safety.The main results are as follows:(1)The ability of wheat roots to absorb PAHs decreased significantly with the growth of the plant,and PAHs accumulated by stems and leaves also decreased at the early stage.After the grain filling period,the difference of PAHs accumulation in stems and leaves decreased gradually due to the slow activities of wheat.The order of PAHs concentration in different parts of wheat at seedling and tillering stage was root>stem>leaf.After the jointing stage,the concentration of PAHs in roots was still significantly more than the overground part,but the difference in the overground parts gradually decreased,and sometimes the PAHs concentration of leaf might be higher than that of stem,which was related to the change of lipid content in each part of wheat.The concentration of three kinds of PAHs in wheat roots was shown as phenanthrene>naphthalene>pyrene,and the concentration of phenanthrene was significantly higher than naphthalene and pyrene,while the concentration order in stems was naphthalene>phenanthrene>pyrene,and the concentrations of naphthalene and phenanthrene in leaves were almost the same,but higher than pyrene.At the early stage,the transfer factor of root-stem was higher than that of root-leaf.At the later stage,the accumulation of PAHs in stems started to decrease,more PAHs absorbed by roots transfered to the leaves,thus the difference between the two transfer factors became small.The concentration of PAHs transfered from root to seed was higher than that from leaf to seed.3 PAHs concentrations in seeds were naphthalene>phenanthrene>pyrene.(2)Through the construction of 2-DE maps and the analysis of MALDI-TOF/TOF MS,it was found that there was a significant reduction in castor xylem sap proteins under the stress of phenanthrene.PDQuest was used for matching analysis.By comparing the maps of three groups,it was found that there were 20 different proteins in the 4 h group and 37 different proteins in the 24 h group.The MALDI-TOF/TOF MS analysis showed that 25 proteins were inhibited after phenanthrene treatment for 24 h,including ribosomal protein and aspartic proteinase nepenthesin,and there were 34 proteins were inhibited after 4 h and 24 h phenanthrene treatment,including sucrose synthase,and glyceraldehyde-3-phosphate dehydrogenase,etc.The reason may be that after absorption by castor root,phenanthrene will be transported upward through xylem vessel,and its toxicity inhibits the expression of various proteins in castor xylem sap.These proteins play a crucial role in physiological processes such as plant growth and development,stress tolerance,and gene expression regulation,thus they may affect plant growth and development and cause abnormal development.While many proteins were inhibited,six additional proteins were detected in the castor xylem sap in response to the stress of phenanthrene.(3)PAHs concentration in each part of wheat decreased with the increase of biochar concentration.The optimal dosage of biochar for the accumulation inhibition of naphthalene,phenanthrene and pyrene were 20 mg/L,40 mg/L and 40 mg/L,respectively.During the whole growth stage,the inhibition effect of biochar on the PAHs absorbed by wheat root was naphthalene>phenanthrene>pyrene.With the gradual growth of wheat,the inhibition effect of overground part for naphthalene gradually decreased,while the inhibition rate of phenanthrene and pyrene was relatively stable.The application of biochar also had an obvious inhibitory effect on PAHs concentrations in wheat grains.The concentrations of naphthalene,phenanthrene and pyrene decreased by 29.93%,28.41%and 23.76%at the grain filling stage and by 28.94%,18.11%and 37.64%at the mature stage.In summary,different parts of wheat have different degrees of accumulation of the three PAHs,and the concentration of the underground part is significantly higher than that of the overground part In the seedling stage,the concentration was the highest,and gradually decreased with the growth of the plants.The application of biochar can effectively inhibit PAHs accumulation,and the best inhibition effect is in the seedling stage.When the phenanthrenes absorbed by roots are transported upward through the xylem,it can significantly inhibit the expression of proteins in the xylem sap.Meanwhile,several new proteins were increased to cope with PAHs stress. |
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