Effects Of The Ionic Liquid1-Hexyl-3-Methylimidazolium Bromide On Root Gravitropismin Arabidopsis Seedlings

Ionic liquids?ILs?are a kind of molten salt,composed of large asymmetric organic cations and small organic or inorganic anions.The ILs with different structure or nature usually can be synthesized through different combinations of cations and anions Based on the physicochemical properties,such as negligible vapor pressure,non-volatility,high stability and powerful solvation potential,ILs have been regarded as“green” solvents.The characterization of ILs facilitates the wide application in various fields,including organic synthesis,electrochemistry,catalysis,and extraction and isolation processes.Therefore,ILs could make their way into the natural environment and the impact on living organisms must be taken into consideration thoughtfully.Due to the wide application of ionic liquid,the research papers and reports about ionic liquid also showed in an increasing trend year by year.At the same time,the synthesis of ionic liquid and the related patent application also presents incremental stages of development.The depth study of ionic liquid and its wide range of applications inevitably also brings a series of negative effects.Compared with other ILs,imidazolium-based ionic liquids are the most commonly investigated group and applied to academic research and industrial uses.Many evidences have indicated that ionic liquids present toxicity to organisms.The toxicity of ionic liquids has become a hot spot in the field of biological effects in recent years,including microorganisms,algae,terrestrial invertebrates,vertebrates,as well as human cell lines.However,the information about the toxic effect of ILs on higher plants and the molecular mechanism underlying the toxicity still remains limited.The previous reports about the toxic effects of ILs on plants mainly focus on prowth parameters,antioxidant system and photosynthetic activity.While,the knowledge about the effects of ILs on gravitropism in plants is still unclear.Given that root gravitropism is a necessary physiological event for plants to anchor themselves in to the oil and find resources needed for growth and development,the aim of the present study was to examine the responses of root gravitropism in Arabidopsis seedlings to [C₆mim]Br treatment comprehensively from the cell biological and molecular level for the first time.This work provides new information on the environmental safety evaluation of ILs.Our results showed that:?1?the root growth and gravity response were significantly inhibited with increasing IL concentration.At the concentration with 80 mg L-1,the root growth was inhibited to the mostserious extent and root almost stopped growing.The treatments at 40 and 60 mg L-1 showed a obvious delayed root gravity responses during 10-12 h gravity stimulus.?2?Given that starch-filled amyloplasts function as the statoliths involved in root gravity response,the dispersed distribution of amyloplasts was obviously observed by IL treatment at higher concentration.In addition,the amount of amyloplasts in IL-treated roots was significantly reduced in comparison with that in controls.?3?The auxin distribution labelled with DR5rev::VENUS was altered in IL-treated seedlings.The signal intensity and gene expression of auxin efflux carriers PIN2 and PIN3 were obviously decreased by IL exposure.Moreover,as consequences in response to gravity stimulus,the asymmetric DR5 signals in control root apex were impaired by IL treatment.?4?The predominant PIN2 signals along the lower flank of root and PIN3 polarization in columella cells were also significantly reduced in seedlings exposed to IL.?5?Our results suggest that the ionic liquid [C₆mim]Br affects the amount and distribution of starch granules,and disturbs the deployment of PIN2 and PIN3,thus impairing auxin flows in response to gravity stimulus and causing deficient root gravitropism in Arabidopsis seedlings.In summary,our results showed that the root growth and gravity response in Arabidopsis seedlings were significantly inhibited with increasing IL concentration.By treatment with [C₆mim]Br,the number of starch-filled amyloplasts is reduced,and distribution pattern of starch-filled amyloplasts is disrupted.Moreover,the ILs influenced the auxin distribution and deploymen of auxin transporters.Thus,the toxic effects of [C₆mim]Br by influencing the growth of root,ultimately affect the plant growth and development.