Hyperaccumulation of metal in the apoplast contributes to the tolerance of the phytoremediator <i>Pistia stratiotes</i> L. to manganese-contaminated water

Phytoremediation of manganese (Mn)-contaminated water requires the selection of Mn-tolerant species. This study reports on physiological changes and Mn bioaccumulation in the aquatic macrophyte <i>Pistia stratiotes</i> cultivated under various MnCl₂ concentrations: control, 80, 340, 600, 1000, 2000, and 4000 µM. Few visual symptoms of Mn toxicity, such as chlorosis, were observed after 10 days, especially in plants treated with 2000 and 4000 µM MnCl₂. High Mn accumulation was recorded, with maximum values of 23,700 and 24,600 µg g^-1 DW in the shoots and roots, respectively, at 4000 µM Mn, contrasting with 825.01 and 1587.53 µg g^-1 DW in control plants. Cellular fractioning showed that Mn in shoots and roots was mainly associated with the cell wall, with approximately 90% of the Mn in roots detected in the apoplast. There were no significant changes in net CO₂ assimilation or respiratory rates after 5 and 10 days of Mn exposure. These results demonstrate that <i>P. stratiotes</i> is a Mn hyperaccumulator species with excellent phytoremediation potential, as shown by its high bioaccumulation capacity and its ability to maintain photosynthetic efficiency under Mn stress.