| PAHs pollution is a pressing environmental problem for human beings and also a huge threat for human health. At present, the study about PAHs stress on plants is lacking and the correlative reports are limited. What's more, the study about PAHs physiological stress on Arabidopsis hasn't been reported. Therefore, choosing Arabidopsis as the material and ubiquitous four-ring aromatic hydrocarbons Fluoranthene and three-ring aromatic hydrocarbons Phenanthrene as the object, the research studied growth,cell ultrastructure and physiological response of Arabidopsis to PAHs stress under the solid MS medium culturing condition with different PAHs concentration and time. The main study results were as follows:1,The growth of Arabidopsis was inhibited by Fluoranthene stress. The stress symptoms appeared as: seedling diminished, leaves diminished and lessened with etiolation, root system was dumpy and lessened, injury sysptoms aggravated with Fluoranthene concentration rising. Also, Phenanthrene stress inhibited the growth of Arabidopsis. But injury symptoms to Phenanthrene stress were more serious than Fluoranthene, appearing .that seedlings were dead under 1．00mmol·L-1 and 1．25mmol·L-1 Phenanthrene stress. Comparing with control, the rate of germination clearly descended, germination time postponed, some seedlings were dead, the root length clearly shortened, the time of root-emergence postponed, chloroplast distorted and expanded, lamellae weren't clear and arranged irregularly, mitochondrion was blurry, and several cells disorganized under the treatments of 1．00mmol·L-1 Phenanthrene stress.2,Fluoranthene stress with different concentration induced the change of physiological characteristic in Arabidopsis, especially the change about active oxygen metabolism. It showed as follows. With Fluoranthene stress concentration rising, chlorophyll content reduced, SOD activity enhanced, CAT activity firstly descended then ascended and finally descended, POD activity and APX activity firstly ascended then descended, the content of GSH,H2O2 and MDA increased to different extent in Arabidopsis leaves. Comparing with control, chlorophyll content extremely remarkably reduced and MDA content extremely remarkably increased in the treatments of stress concentration higer than 0．25mmol·L-1 , SOD activity,POD activity,GSH content and H2O2 content were all extremely remarkably enhanced in all the Fluoranthene stress treatments. At the same time, when stress concentration ascended from 1．00mmol·L-1 to l.25mmol·L-1 , SOD activity remarkably enhanced; POD activity was the highest under 1．00mmol·L-1 Fluoranthene stress, then started to descend extremely remarkably; APX activity was the highest under 0．75mmol·L-1 Fluoranthene stress, then also started to descend extremely remarkably. It indicated that active oxygen producing on and on in Arabidopsis induced the change of antioxidase activity and GSH content; that SOD activity enhanced to reduce cumulation of O2 ; that CAT activity was more hypersensitive to Fluoranthene stress and was clearly inhibited; that POD activity APX activity firstly enhanced, showing adaptability to some extent and enhancing the ability of eliminating H2O2, then separately came to the highest values at 1．00mmol·L-1 and 0．75mmol·L-1 Fluoranthene stress concentration, after it, POD activity and APX activity extremely remarkably descended and the ablity of eliminating H2O2 abased; that GSH content increased to enhance the ability of eliminating H2O2; that under the synergetic effect of antioxidase and GSH, H2O2 wasn't eliminated in time so that it resulted in the cumulation of H2O2, accordingly conduced that chlorophyll decomposed and lipid peroxidation aggravated, appearing as the increasement of MDA content, thereby hurt membrane system, accordingly hurt Arabidopsis cells, finally resulted in aggravation of Arabidopsis injury sysptoms; that 0．75mmol·L-1～1．00mmol·L-1 might be a limit to maintain the balance of producing and eliminating active oxygen free radical to Fluoranthene stress and a start to lose renovating ability in Arabidopsis, the further studies should be done.3,As the same as Fluoranthene stress with different concentration, Phenanthrene stress with different concentration also induced the change of physiological characteristic in Arabidopsis, especially the change about active oxygen metabolism.The study results were similar to related results in 2, but comparing with Fluoranthene stress, the originating concentration that SOD activity,POD activity,APX activity and GSH content were hypersensitive to Phenanthrene and the concentration that POD activity and APX activity came to the highest value correspondingly moved up. It showed as follows. When stress concentration ascended from 0．75mmol·L-1 to 1．25mmol·L-1 , SOD activity remarkably enhanced; POD activity was the highest under 0．25mmol·L-1 Phenanthrene stress, and it extremely remarkably descended when stress concention ascended from 0．50mmol·L-1 to 0．75mmol·L-1 ; APX activity was the highest under 0．25mmol·L-1 Phenanthrene stress and extremely remarkably descended after it; When stress concentration ascended from 1．00mmol·L-1 to 1．25mmol·L-1 , GSH concent remarkably enhanced. It was considered that injury mechamism of Arabidopsis was the same as what was related in 2, but hypersensitive extent to Phenanthrene was higher than hypersensitive extent to Fluoranthene in Arabidopsis. And 0．25mmol·L-1 might be a limit to maintain the balance of producing and eliminating active oxygen free radical to Phenanthrene stress and a start to lose renovating ability in Arabidopsis, but it needed further study.4,Phenanthrene stress with different time also induced the change of physiological characteristic in Arabidopsis, especially the change about active oxygen metabolism.lt appeared as follows. With the time extending, chlorophyll content,POD activity,APX activity,GSH content,H2O2 content and MDA content all enhanced and CAT activity descended in both control and 1．00mmol·L-1 Phenanthrene stress treatment; SOD activity in control enhanced, while SOD activity in 1．00mmol·L-1 Phenanthrene stress treatment firstly ascended then descened and it came to the highest value at 48h. Comparing with control, chlorophyll content in 1．00mmol·L-1 Phenanthrene stress treatment reduced, the diffenence of two treatments was not remarkable in short time, with the time extending, it was extremely remarkable; SOD activity and POD activity extremely remarkably enhanced, while CAT activity and APX activity extremely remarkably descended; GSH content reduced at 12h, but it extremely remarkably enhanced with the time extending; H2O2 content and MDA content both enhanced, to H2O2 content, the difference of two treatments was not remarkable at 12h but remarkable with the time extending. It was considered that the rising of stress concentration or the extending of stress time meaned the aggrandizement of stress extent. With the stress extent aggrandizing, active oxygen produced on and on in Arabidopsis, and antioxidase and antioxidant GSH could act active synergetic effect to maitain dynamic balance of producing and eliminating active oxygen free radical in Arabidopsis, accordingly made metabolization in Arabidopsis normally function. However, when the synergetic effect couldn't eliminate active oxygen free radical in time, such as H2O2, it would result in the cumulation of H2O2, accordingly conduced that chlorophyll decomposed and lipid peroxidation aggravated, appearing as the increasement of MDA content, thereby hurt membrane system. |
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