The intracellular water volume modulates the accumulation of cadmium in Euglena gracilis

• Published in: Algal research (Amsterdam) Vol. 46; p. 101774
• Main Authors: Sánchez-Thomas, Rosina, García-García, Jorge D., Marín-Hernández, Álvaro, Pardo, Juan P., Rodríguez-Enríquez, Sara, Vera-Estrella, Rosario, López-Macay, Ambar, Moreno-Sánchez, Rafael
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.03.2020
• Subjects: Aquaporin; Cadmium; Cellular volume; Euglena; Osmolytes; Osmotic pressure; MTG; 50Cd; Spd; t-BHP; Euglena; Gly; γ-EC; Cys; GSH; PolyPs; AQP; GSSG; Cadmium; 200Cd; Cad; APx; GR; GPx; Put; Osmolytes; PCA; AAS; β-Ala; His; TCA; PolyGSH; Ala; ROS; Osmotic pressure; Cellular volume; Aquaporin
• ISSN: 2211-9264; 2211-9264
• DOI: 10.1016/j.algal.2019.101774

In order to describe a relatively novel mechanism associated to heavy metal resistance in Euglena gracilis, the osmotic responses during cadmium accumulation were analyzed. Several physiological/biochemical parameters were assessed in E. gracilis exposed to 50 and 200 μM Cd2+, concentrations well within the range found in polluted soils and aquatic environments. The Cd2+ accumulation attained after only 24 h exposure induced marked increases in both the intracellular water volume and cellular size, which were maintained for several days; these changes correlated with (i) an increased intracellular osmolarity (i.e. osmotic pressure) driven by a generalized increase in the osmo-metabolites (trehalose, phosphate-molecules, amino acids, thiol-molecules, betaines and polyamines) content; and (ii) the triggering of antioxidant defenses (increased GSH/GSSG ratios and GPx, GR and APx activities). In contrast, no changes in intracellular volume, cellular size and antioxidant status were observed under hyperaccumulation of Zn2+. Furthermore, E. gracilis cultured in a hypoosmotic medium promoted greater Cd2+ accumulation and water volume, compared to a hyperosmotic medium. These changes were significantly decreased by the aquaporin inhibitors Hg2+ and pentamidine. The results suggested that the cell responses to Cd2+ and osmotic stress share biochemical mechanisms in this algae-like protist, in which Cd2+ accumulation closely correlates with the intracellular water volume changes in an oxidative stress-mediated process. [Display omitted] •Cd2+ accumulation increases intracellular water volume in E. gracilis.•Zn2+ accumulation does not induce osmotic changes.•Higher intracellular water content allows a greater Cd2+ accumulation.•Water uptake is mediated by Hg2+ and pentamidine-sensitive aquaporins.•Cd2+ induces osmotic changes through an antioxidative stress-dependent process.