Comparing analysis of elements sub-cellular distribution in Kandelia obovata between SEM-EDX and chemical extraction

•Image analysis allowed us to detect the distribution of metals in K. obovata tissue.•Cell wall binding was involved in metal tolerance of K. obovata.•The root epidermis provided a major barrier to the transport of metals in K. obovata.•Metal detoxification was influenced by the sub-cellular fractions.

The mangrove plant Kandelia obovata Sheue, Liu & Yong sp. nov. can sequestrer and inherently tolerate high metal concentrations in polluted estuary wetlands. Sequential extraction and scanning electron microscopy coupled with energy-dispersive X-ray microanalysis (SEM-EDX) were used to determine the cellular distribution and chemical forms of Cu, Zn, Pb and Cd in this mangrove. Metals were largely confined to roots compared to the aerial parts. All plant tissues of K. obovata followed a gradient with the sequence: cell wall > intercellular space. The root epidermis provided a major barrier to the transport of metals. In roots of 50 mg L−1 Cd(II) treatment, SEM-EDX confirmed that the highest Cd concentration was found in epidermal cells. Cd was distributed mainly along the walls of epidermis, cortex, endodermis and some xylem parenchyma. Other metals showed a similar distribution trend. The sub-cellular distribution pattern of metals is probably involved in tolerance mechanisms of K. obovata.

Graphical abstractElement dispersion in K. obovata root identified by SEM-EDS.Figure optionsDownload full-size imageDownload as PowerPoint slide