Effects of amino acid ionic liquids with different cations ([N2Py], [N2222], [P2222], and [C2mim]) on wheat seedlings

Abstract

The ecotoxicity of four ionic liquids with different cations (N-ethyl-pyridine alanine [N₂Py][Ala], tetraethyl phosphine L-α-amino propionic acid salt [P₂₂₂₂][Ala], 1-ethyl-3-methyl-imidazolium alanine [C₂mim][Ala], and tetraethyl ammonium L-α-amino propionic acid salt [N₂₂₂₂][Ala]) was assessed in hydroponically-grown wheat seedlings at concentrations from 200–1200 mg L⁻¹. The results showed that type of cation has a significant influence on the growth, chlorophyll and nutrient uptake of wheat seedlings (P < 0.05). We observed decreased dry weight and shorter roots and shoots in the treated seedlings with increasing IL concentrations. The contents of Chl a and Chl b in wheat seedlings exposed to ILs showed the trend of firstly increasing followed by a decrease with increasing IL concentrations, but they peaked at different concentrations of ILs. In addition, the exposure of wheat seedling to ILs containing different cations (200–1200 mg L⁻¹) led to first an increase and then a decrease of nitrogen content, and reduced the content of phosphorus and potassium. Moreover, the cellular structures, including nuclei, mitochondria, chloroplasts, cell membranes, and the cell walls of wheat leaf and root were affected to varying degrees by 600 mg L⁻¹ ILs. The negative impacts of ILs on wheat seedlings ranked from high to low were: [N₂Py][Ala] > [N₂₂₂₂][Ala] > [P₂₂₂₂][Ala] > [C₂mim][Ala]. In this work, the relatively stronger toxicity of [N₂Py][Ala] was likely contributed by ethanol, which was used to dissolve [N₂Py][Ala]. Therefore, it is not recommended to use N-ethyl-pyridine alanine ([N₂Py][Ala]) widely in practical applications.