Combined forms of Pb and its detoxification and absorption in Cladophora rupestris subcells

This study aims to analyze the combined form, detoxification, and adsorption mechanism of Pb in Cladophora rupestris subcells. The chemical form analysis at different concentrations (0, 0.5, 1.0, 2.5, 5.0, 7.5, and 10 mg/L) indicated that most of the Pb (37%-76%) were integrated with oxalate and undissolved phosphate, which were important to the detoxification of C. rupestris. The characterization of Pb (0, 0.5, and 5.0 mg/L) at the subcellular was conducted via Fourier-transform infrared spectroscopy (FTIR), Three-dimensional excitation-emission matrix spectroscopy (3D-EEM), and protein secondary structure fitting. Results revealed that Pb-polysaccharides ((C6H5)-OO-Pb-OH, C-O-Pb, and symmetric Pb-O-Pb), Pb-functional-groups ((C6H5)-COO-Pb and (C6H5)-P = O-Pb), and Pb-protein complexes (OH-C7H6-CN-Pb-COOH, C9H10-NH-CN-C = O-Pb, Pb-S-C, and Pb-S) were formed. The cell wall produced transport proteins, such as metallothionein and glutathione, which bound and helped Pb2+ enter the cell. After entering the soluble fraction, the Pb-organic acid ((C6H5)-COO-Pb, (C6H5)-O-Pb, and (C6H5)-P = O-Pb) and Pb-sulfhydryl compound (Pb-S-C/Pb-S) assumed the most important role in resisting the toxicity of Pb2+. Pb2+ was absorbed in the organelle and formed (C6H5)-C-O-Pb and (C6H5)-P = O-Pb, and complexed with protein (Pb-C-N) when treated with 5.0 mg/L Pb. Results could help understand the role of subcellular fraction in the algal adaptation to stressful heavy metal conditions. (C) 2020 Elsevier B.V. All rights reserved.