Cellular and subcellular distribution and factors influencing the accumulation of atmospheric Hg in Tillandsia usneoides leaves

Highlights: • Atmospheric Hg circulates dynamically in the surface and internal structures of T. usneoides leaves. • Hemicellulose is the primary Hg-binding component of the cell wall. • Functional groups -OH and COO- play a vital role in the Hg accumulation process. Atmospheric Hg is a highly toxic heavy metal with bioaccumulative properties. However, relatively few studies have focused on the distribution of Hg in cellular and subcellular structures of plants and factors influencing its accumulation. In this study, we selected Tillandsia usneoides, which is a widely used bioindicator for Hg, to analyze the concentration of Hg in different cells (foliar trichomes, epidermal cells, mesophyll cells, and vascular bundle cells), different subcellular structures (cell wall, cell membrane, vacuoles, and organelles) and different cell wall components (pectin, hemicellulose 1, and hemicellulose 2). It was determined that Hg was present in different types of cells, but there was no significant difference, suggesting that atmospheric Hg circulates dynamically in the surface and internal structural cells of T. usneoides leaves. Subcellular analysis showed that as Hg concentration increased, more Hg accumulated in the vacuoles and cell wall through the compartmentalization mechanism. Hemicellulose had the highest content of Hg, indicating that it is the primary Hg-binding component of the cell wall. The FTIR analysis results showed that after the Hg treatment, the cell wall -OH and COO- absorption peaks changed most significantly, indicating that these functional groups play a vital role in the Hg accumulation process.