Mechanical properties of Callitriche cophocarpa leaves under Cr(VI)/Cr(III) influence

Submersed Callitriche cophocarpa is an outstanding Cr phytoremediator in water systems. The mineral elements in waters can penetrate the submersed plant surface. This has led us to the hypothesis that the absorbed Cr can alter the mechanical properties of leaves. These properties were measured by applying atomic force microscopy. C. cophocarpa shoots were immersed in 100 A mu M (5.2 mg/l) Cr solution for 7 days. Cr was applied independently at two distinct oxidation states as Cr(VI) and Cr(III), known from different physicochemical properties and toxic effects. The contents of elements which were proportional to the fluorescence signal in individual leaves were evaluated using micro-X-ray fluorescence spectroscopy. The results obtained showed that the leaf epidermis significantly changes its elastic properties upon incubation with Cr-supplemented solution. When compared to the control, a drop in the leaf's stiffness observed for Cr(III) was ca. 42 %. In the case of Cr(VI)-treated leaves, the stiffness raised to ca. 17 %. The changes in elasticity were significantly correlated with the contents of Ca (Pearson's coefficient r = 0.87, p < 0.017). The results led us to ascertain that it is Cr(III) but not Cr(VI) that significantly influences Ca removal from leaves thus decreasing the stiffness of the leaf's epidermis.