Physiological and Antioxidant Responses of Germinating Mung Bean Seedlings to Phthalate Esters in Soil

Abstract

Single phytotoxicity of two representative phthalate esters (PAEs), di-n-butyl phthalate (DnBP) and bis(2-ethylhexyl) phthalate (DEHP), was tested in mung bean (Vigna radiata) seedlings germinated for 72 h in soils spiked with varying concentrations (0-500 mg kg⁻¹ soil) of DnBP or DEHP. PAEs added at up to 500 mg kg⁻¹ soil exerted no significant effect on germination but both pollutants significantly inhibited root elongation (P < 0.01), DEHP inhibited shoot elongation (P < 0.01) and DnBP depressed biomass on a fresh weight basis (P < 0.05). Seedling shoot and root malondialdehyde (MDA) contents tended to be stimulated by DnBP but inhibited by DEHP. However, increases in superoxide dismutase, peroxidase, ascorbate peroxidase and polyphenol oxidase activities, as well as glutathione (GSH) content, were induced at higher concentrations (e.g., 20 mg kg⁻¹) of both compounds. Accumulation of proline in both roots and shoots and the storage compounds, such as free amino acids and total soluble sugars, in whole plant was induced under the stress exerted by both PAEs. The general responses of mung bean seedlings indicated higher toxicity of DnBP than DEHP on primary growth, during which root elongation was a more responsive index. MDA and GSH were more sensitive parameters in the roots than in the shoots and they might be recommended as physiologically sensitive parameters to assess the toxicity of PAE compounds in soils in future long-term studies.