Some species of Diospyros form the black wood that is known as ebony. Infrequently, D. kaki forms wood with black patterning that is called “kurogaki” in Japan and is highly valued. To understand the mechanism of formation of the blackened xylem, we attempted to clarify the pathways of diffusion of colored substances from the site of their biosynthesis to their deposition in secondary xylem. We observed colored substances in pits and intercellular spaces and we recorded the deposition of colored substances in the cell walls of wood fibers. In gray and black regions, we found colored substances in the pits between xylem cells, in blind pits and in intercellular spaces. At the boundary between whitish and black regions, areas of coloration in the cell walls of wood fibers gradually increased in size from the whitish to the black regions. Heavy deposition of colored substances was observed in the inner region of the secondary walls of wood fibers. Furthermore, coloration of the outer region of the secondary walls and compound middle lamella (CML) of wood fibers gradually became stronger toward the black regions. Our observations suggest that pit-pairs and intercellular spaces might provide the pathways for inter- and extracellular diffusion of colored substances, respectively. In addition, colored substances might penetrate the cell walls of wood fibers, moving from the lumen into the cell wall.

中文翻译：

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柿木发黑木质部中有色物质在细胞外和细胞间扩散的途径

柿属的某些物种形成了被称为乌木的黑木。D. kaki很少会形成带有黑色图案的木材，在日本被称为“ kurogaki”，并且备受重视。为了理解发黑木质部形成的机理，我们试图阐明有色物质从其生物合成位点扩散到其在次生木质部中的沉积的途径。我们在坑和细胞间空间中观察到有色物质，并记录了有色物质在木纤维细胞壁中的沉积。在灰色和黑色区域，我们在木质部细胞之间的凹坑中，盲孔和细胞间空间中发现了有色物质。在发白和黑色区域之间的边界处，木纤维的细胞壁中的着色区域的尺寸从发白到黑色区域逐渐增大。在木纤维次壁的内部区域观察到有色物质的大量沉积。此外，次生壁的外部区域和木纤维的复合中间层（CML）的着色朝向黑色区域逐渐增强。我们的观察表明，凹坑对和细胞间空间可能分别为有色物质在细胞内和细胞外扩散提供了途径。此外，有色物质可能会渗透到木纤维的细胞壁，从内腔进入细胞壁。我们的观察结果表明，凹坑对和细胞间空间可能分别为有色物质在细胞内和细胞外扩散提供了途径。此外，有色物质可能会渗透到木纤维的细胞壁，从内腔进入细胞壁。我们的观察结果表明，凹坑对和细胞间空间可能分别为有色物质在细胞内和细胞外扩散提供了途径。此外，有色物质可能会渗透到木纤维的细胞壁，从内腔进入细胞壁。