Electron Microscopy Observation of Biomineralization within Wood Tissues of Kurogaki

Abstract

Interactions between minerals and microorganisms play a crucial role in living wood tissues. However, living wood tissues have never been studied in the field. Fortunately, we found several kurogaki (black persimmon; Diospyros kaki) trees at Tawara in Kanazawa, Ishikawa, Japan. Here, we report the characterization of kurogaki based on scanning electron microscopy equipped with energy-dispersive spectroscopy (SEM-EDS) and transmission electron microscopy (TEM), associated with inductively coupled plasma-mass spectrometry (ICP-MS) analyses, X-ray fluorescence analyses (XRF) and X-ray powder diffraction (XRD) analyses. This study aims to illustrate the ability of various microorganisms associated with biominerals within wood tissues of kurogaki, as shown by SEM-EDS elemental content maps and TEM images. Kurogaki grows very slowly and has extremely hard wood, known for its striking black and beige coloration, referred to as a “peacock pattern”. However, the scientific data for kurogaki are very limited. The black “peacock pattern” of the wood mainly comprises cellulose and high levels of crystal cristobalite. As per the XRD results, the black taproot contains mineralized 7 Å clays (kaolinite), cellulose, apatite and cristobalite associated with many microorganisms. The chemical compositions of the black and beige portions of the black persimmon tree were obtained by ICP-MS analyses. Particular elements such as abundant Ca, Mg, K, P, Mn, Ba, S, Cl, Fe, Na, and Al were concentrated in the black region, associated with Pb and Sr elements. SEM-EDS semi-qualitative analyses of kurogaki indicated an abundance of P and Ca in microorganisms in the black region, associated with Pb, Sr, S, Mn, and Mg elements. On the other hand, XRF and XRD mineralogical data showed that fresh andesite, weathered andesite, and the soils around the roots of kurogaki correlate with biomineralization of the black region in kurogaki roots, showing clay minerals (kaolinite) and cristobalite formation. In conclusion, we describe how the biominerals in the black region in the cellulose within wood tissues grow chemically and biologically in the sap under the conditions associated with the beige portions of the taproot. This can explain why the crystals produce the “peacock pattern” in the kurogaki formed during the year. We conclude that kurogaki microbiota are from bacteria in the andesitic weathered soil environment, which produce silicification. In other words, the patterned portions of kurogaki consist of silicified wood.