Effect And Molecular Reponse Mechanism Of Imidazolium-based Ionic Liquids On Arabidopsis Thaliana

Because of the good physical and chemical properties,ionic liquids(ILs)are considered as "green solvents" to replace the conventional or-ganic solvent.Though the low volatility of IL significantly reduce its pollution to the atmoshphere,the high water solubility may release it to the aquatic environment,the accumulation of IL could cause potential threats to aquatic and soil ecosystems.The effects of three imidazoli-um-based ILs with different alkyl chain lengths,including 1-octyl-3-methylimidazolium chloride([C8mim]Cl),1-decyl-3-methylimidazolium chloride([C10mim]Cl),and 1-dodecyl-3-methylimidazolium chloride([C12mim]Cl)on growth,cell structure,photosystem,oxidative stress and molecular mechanism of Ar-abidopsis thaliana were investigated.The results showed that the fresh weight of leaves and root lengths decreased with the alkyl chain length and concentrations of ILs increased.As IL concentration and alkyl chain length increasing,the vein clearing,leaf chlorosis,and browning on the A.thaliana leaf abaxial surface oc-curred,and cell membrane permeability were significantly affected by ILs,with a dose-response relationship.Plasmolysis and the chloroplast swelling occurred,the number and size of starch granules and osmiophi-lic globules increased in[C8mim]Cl,[C10mim]Cl treatments and on aged leaves in[C12mim]Cl treatment.The toxicity of ILs increased with in-creasing alkyl chain length.But no significant damages occurred on new leaves of[C12mim]Cl treatment,perhaps due to plant self-protection of newly-growing leaves.The chlorophyll contents of the whole plants,older leaves decreased with the increasing ILs contentrations and alkyl chain lengths.The inhibi-tion of[C12mim]Cl treatment was the greatest,followed by[C8mim]Cl and[C10mim]Cl treatment,but the chlorophyll contents of newly-growing leaves were higher than that of the control group,which may due to the self-protective mechanisms of plants.Chlorophyll fluorescence parame-ters of photosynthetic system ?(PSII),including minimal fluorescence yield(FO),maximal fluorescence yield(Fm),potential efficiency of PSII(Fv/F0),maximum quantum efficiency of PSII photochemistry(Fv/Fm),photochemical quantum yield[Y(?)],yield of other non-photochemical losses(NO),non-photochemical quenching coefficient without measuring F0'(NPQ),and relative electron transport rate(ETR)of newly-growing leaves,were all affected in[C8mim]Cl and[C10mim]Cl treatments.As for[C12mim]Cl treatments,the chlorophyll fluorescence of older leaves were seriously affected,while there were no significant changes in new-ly-growing leaves,the result may due to the plant self-protection of new-ly-growing leaves.The contents of reactive oxide species(ROS)and malonaldehyde(MDA)increased with the increasing ILs concentrations and alkyl chain lengths.The contens of ROS and MDA in[C12mim]Cl treatments were higher than[C10mim]Cl and[C8mim]Cl treatments.At different concen-trations,low IL contentration treatment could promote the production of soluble protein to maintain normal plant metabolism,while high IL con-tentration treatment could inhibited the soluble protein,it suggested that the external stress exceeds the tolerance of plants,caused cell damage.As the IL concentration increasing,the antioxidant enzyme of A.thaliana in-cluding superoxide dismutase(SOD),catalase(CAT)and glutathione(GSH)first increased then decreased,the activity of antioxidant enzyme would be inhibited while the toxic stress exceeds the tolerance of plants.However,the activity of peroxidase(POD)increased with increasing IL contentration and alkyl chain length,it may due that plant eliminate the hydrogen peroxide(H2O2)steadily to maintain its dynamic balance after plant was induced by ROS.The gene expression of[C8mim]Cl treatments was most similar to the control group,followed by[C10mim]Cl and[C12mim]Cl treatments.The first principle component of[C8mim]Cl and[C10mim]Cl treatments was close to the control group,while obvious differences existed between[C12mim]Cl treatments and control group.The concentration level of[C8mim]Cl and[C10mim]Cl treatments in various metabolic pathways was low,it showed that the photosynthesis was inhibited in all IL treat-ment,and the protein synthesis was blocked in[C12mim]Cl treatments.The protein profiling of[C8mim]Cl treatments was most similar to the control group,while the protein profiling of[C10mim]Cl treatments was similar to the[C12mim]Cl treatments.The first and second principle component of three ILs treatments was different with the control group.The synthesis of secondary metabolite in[C8mim]Cl treatments was up-regulated,suggesting the adversity stress.The expression level of down-regulated protein in[C10mim]Cl and[C12mim]Cl treatments was higher than[C8mim]Cl treatments,the down-regulated protein could cause the loss of normal physiological function in A.thaliana,which showed as metabolic disturbance,and the mechanism of response to stress would be arised.