Effect Of Ionic Liquids On The Growth, Physiology And Photosynthetic Indexes Of Wheat Seedlings

An ionic liquid is a salt with low melting point composed of organic cation and inorganic/organic anion, usually in liquid state at room or low temperature. Such salts are usually called room ionic liquids (RILs). By virtue of their outstanding physical and chemical properties, ionic liquids have been used in many fields. During the application, release of ionic liquids to the environment is inevitable. Therefore, it is necessary and important to study their toxic effect and potential risk, especially the effect on crops.In this paper, hydroponic and soil-cultured wheat were chosen as the experimental material. The toxic effects of different concentrations of ionic liquids (100,200,300,400,500 mg·L^-1), i.e. 1-methyl-3-ethyl-imidazolium bromide ([C₂mim][Br]), 1-methyl-3-ethyl-imidazolium valinate ([C₂mim][Val]), and 1-methyl-3-butyl-imidazolium bromide ([C₄mim][Br]), on the growth, physiological and photosynthetic indexes of wheat in seed germination and seedling development period were studied. The results showed that:(1) All of these three kinds of ionic liquids showed inhibitory effect on wheat seed germination which was also increased with their concentrations.(2) Based on the data of plant height and biomass of the aerial part, [C₂mim][Br] and [C₄mim][Br] both inhibited the leaf growth of wheat. Whereas, the leaf growth of wheat was enhanced by low concentrations of [C₂mim][Val] (100, 200 mg·L^-1), but inhibited by high concentrations (300⁵00 mg·L^-1). All the inhibitions were enhanced by increasing their concentrations.Based on the root length and biomass of the underground part, [C₂mim][Br] and [C₄mim][Br] both inhibited the root growth of wheat. For [C₂mim][Val], only when the concentration was 100 mg·L^-1, it showed enhancement on root growth; but at other concentrations, the root growths were all inhibited by [C₂mim][Val]. All the inhibitions were enhanced by increasing their concentrations.(3) With the time elapse of this experiment, the enzyme activity of wheat was also inhibited by ionic liquids. The inhibition was increased with ionic liquids'concentration. Due to the significant decreasing activities of superoxide dismutase (SOD) and peroxidase dismutase (POD), membrane-lipid peroxidation took place, thus leading to the increase of malondialdehyde (MDA) content.(4) Compared to the control groups, the chlorophyll contents of wheat leaves were lower in all ionic liquids treated groups, which suggests all of these three ionic liquids inhibited the accumulation of the chlorophyll content, and this inhibitory effect increased with the ionic liquid's concentration.(5) All of these three kinds of ionic liquids showed inhibitory effect on the photosynthesis which was also increased with their concentrations.Based on the above results, we could conclude that, the more concentrated the ionic liquids are, the greater the effect is on the wheat growth, Overall, According to the data, when the concentration was 400 and 500 mg·L^-1, ionic liquids had a great effect on wheat growth; By statistically comparing the data, ionic liquids had more effect on roots than that on leaves; By comparison, we found that, the longer the carbon side chain is, the greater the toxic effect is on plants. The ionic liquids with halogens as anions are more toxic than that with amino acids. Otherwise, compared with disposals of aquaculture and earth culture, we found that wheat growth was ifluented by the ionic liquids in aquaculture environment rather than that in earth culture environment.