Investigation of Aluminum in Symplocaceae: Total Content, Histological Structure, and Enzyme Activities from Different Leaf Ages

Since Symplocaceae is known to be a hyperaccumulator of Aluminum (Al), studies on its accumulation capacity and physiological responses have not been widely investigated. The objectives of this research are to investigate the Al content of different leaf ages of Symplocos fasciculata and Symplocos cochinchinensis using Inductively Coupled Plasma Optical Emission Spectrometry (ICP OES). Moreover, the Al localization within tissues was determined using hematoxylin staining, followed by Scanning Electron Microscopy coupled with Energy-Dispersive X-ray spectroscopy (SEM-EDX) mapping to address the ultrastructural form and determine elemental distribution in the cross-section of the leaf. Additionally, confirmation of the mechanism of Al toxicity in relation to stress-induced oxidative enzymes, including Catalase (CAT), Superoxide Dismutase (SOD), and Peroxidase (POD), as well as the lipid peroxidation product Malondialdehyde (MDA) and Hydrogen peroxide (H₂O₂), serves as stress markers. ICP OES assay reveals a significant influence of leaf age on Al content. S. fasciculata old leaves had the highest Al concentration (39,001 ± 343.48 mg kg¹), while S. cochinchinensis young leaves had the lowest (16,788 ± 187.98 mg kg¹). The histological and SEM-EDX mapping evidence shows Al accumulation in S. fasciculata and S. cochinchinensis increases significantly with leaf age. Al³⁺ accumulation is found in cell walls, epidermal tissue, and the palisade layer, with the highest Al distribution in the old leaf lamina. The leaf ages of both Symplocos species exhibit a significant influence on CAT, POD, MDA, and H₂O₂, whereas SOD activity shows no significant variation. A positive correlation is observed between SOD, POD, MDA, and H₂O₂ in S. fasciculata (r > 0.7), similar to S. cochinchinensis, except for MDA (r = 0.6). This research presents a valuable investigation into the Al accumulation strategies and physiological responses of 2 Symplocos species. © 2026, Walailak University. All rights reserved.