The toxic effects of Cu (II) on the freshwater green algae Chlorella vulgaris and its chloroplast were investigated by detecting the responses of photosynthesis and oxidant stress. The results showed that Cu (II) arrested the growth of C. vulgaris and presented in a concentration- and time-dependent trend and the SRichards 2 model fitted the inhibition curve best. The chlorophyll fluorescence parameters, including qP, Y (II), ETR, Fv/Fm, and Fv/F0, were stimulated at low concentration of Cu (II) but declined at high concentration, indicating the photosystem II (PSII) of C. vulgaris was destroyed by Cu (II). The chloroplasts were extracted, and the Hill reaction activity (HRA) of chloroplast was significantly decreased with the increasing Cu (II) concentration under both illuminating and dark condition, and faster decline speed was observed under dark condition. Activities of superoxide dismutase (SOD) and catalase (CAT) and malondialdehyde (MDA) content were also significantly decreased at high concentration Cu (II), companied with a large number of reactive oxygen species (ROS) production. All these results indicated a severe oxidative stress on algal cells occurred as well as the effect on photosynthesis, thus inhibiting the growth of algae, which providing sights to evaluate the phytotoxicity of Cu (II).

The binding of three imidazolium chloride ionic liquids (ILs) with bovine serum albumin (BSA) were investigated by UV absorption spectra, fluorescence spectra and synchronous fluorescence spectra. The results showed that the UV absorption of the BSA was red-shift, and intensity of UV absorption declined with the increase in concentration of ILs. According to fluorescence spectra, fluorescence quenching of the BSA was happened with ILs added, and the main reason is static quenching. The study of synchronous fluorescence spectra indicated that ILs interacted with tryptophan (Trp) and tyrosine (Tyr) residues, changed the structure and the internal hydrophobic conformation of BSA. The binding constant K and the numbers of binding sites n were obtained by Stern–Volmer equation. For [Bmim]Cl, K = 16.12 L mol−1, n was 0.64; for [Hmim]Cl, K = 31.48 L mol−1, n was 0.70; for [Omim]Cl, K = 355.22 L mol−1, n was 0.99. The binding strength of ILs with BSA is expected to show the trend with the length of carbon chain, [Bmim]Cl < [Hmim]Cl < [Omim]Cl.Graphical abstractHighlights► The study reveal the mechanism of ionic liquids interaction with bovine serum albumin. ► The UV absorption intensity of BSA decreased and red shifted with ILs. ► The fluorescence intensity of BSA static quenched with ILs. ► ILs interaction with the protein close the area of Tyr residues. ► The binding strength with BSA show the trend with the length of carbon chain of ILs.

•The three ILs have phytotoxic on rice growth.•The antioxidant enzyme activities increased first and then declined with ILs concentration increased.•The Hill reaction activity decreased and the PS II of leaves was damaged by ILs.•The toxicity of ILs increased as the alkyl chain length increased as the order: [OMIM]Cl < [DMIM]Cl < [C12MIM]Cl.The effects of three imidazolium chloride ionic liquids (ILs) including 1-octyl-3-methylimidazolium chloride ionic liquid ([OMIM]Cl), 1-decyl-3-methylimidazolium chloride ionic liquid ([DMIM]Cl) and 1-dodecyl-3-methylimidazolium chloride ionic liquid ([C12MIM]Cl) were studied in hydroponically grown rice seedlings. The growth inhibition rate increased and the Hill reaction activity of isolated rice chloroplasts decreased with increasing ILs concentrations. The IC50,5d for stem length was 0.70 mg/L of [OMIM]Cl, 0.15 mg/L of [DMIM]Cl, and 0.055 mg/L of [C12MIM]Cl, respectively. The SOD, POD and CAT activities of chloroplast exhibited initial increases followed by decreases in activity with increasing ILs concentrations. Chlorophyll fluorescence parameters such as the maximum effective quantum yield of PSII(Fv/Fm), the potential activity of PSII(Fv/F0), the yield of photochemical quantum [Y(II)], the photochemical quenching coefficient (qP), the non-photochemical quenching coefficient (NPQ) and the relative electron transport ratio (rETR) were affected, showing that ILs will damage the PSII. The results demonstrated that imidazolium chloride ILs are phytotoxic to rice growth and their photosystem, the toxicity increased as the alkyl chain length increased with the following order: [OMIM]Cl < [DMIM]Cl < [C12MIM]Cl. The results will help to better understand the possible role of the defense mechanism in rice caused by ILs exposure.