Departamento de Botânica, Setor de Ciências Biológicas, Universidade Federal do Paraná, Curitiba, PR, Brazil.
Micron. 2013 Jan;44:312-6. doi: 10.1016/j.micron.2012.08.003. Epub 2012 Aug 18.
Melanins are dark, insoluble pigments that are resistant to concentrated acids and bleaching by oxidising agents. Phytomelanin (or phytomelan) is present in the seed coat of some Asparagales and in the fruits of some Compositae. In Compositae fruits, melanin is deposited in the schizogenous spaces between the hypodermis and underlying fibrous layer. Phytomelanin in Compositae is poorly understood, and there are only speculations regarding the cells that produce the pigment and the cellular processes involved in the secretion and polymerisation of phytomelanin. This report describes the cellular processes involved in the secretion of phytomelanin in the pericarp of Praxelis diffusa, a species with a structure typical of the family. The ovaries and fruits at different stages were fixed and processed according to the standard methods of studies of light microscopy and transmission electron microscopy. Hypodermal cells have abundant rough endoplasmic reticulum and mitochondria, and the nuclei have chromatin that is less dense than other cells. These characteristics are typical of cells that synthesise protein/amino acids and suggest no carbohydrate secretion. The fibres, however, have a dense cytoplasm rich in the Golgi bodies that are associated with vesicles and smooth endoplasmic reticulum, common characteristics of carbohydrate secretory cells. Our results indicate that the hypodermal cells are not responsible for the secretion of phytomelanin, as previously described in the literature; in contrast, this function is assigned to the adjacent fibres, which have an organisation typical of cells that secrete carbohydrates.
黑色素是深色、不溶的色素，能抵抗浓酸和氧化剂的漂白作用。植物黑色素（或植物黑素）存在于一些天门冬目植物的种皮中，以及一些菊科植物的果实中。在菊科植物的果实中，黑色素沉积在真皮和下面的纤维层之间的裂生性空间中。对菊科植物中的植物黑色素了解甚少，关于产生色素的细胞以及黑色素分泌和聚合涉及的细胞过程只有一些推测。本报告描述了 Praxelis diffusa 果皮中植物黑色素分泌涉及的细胞过程，该物种的结构具有该科的典型特征。根据光镜和透射电镜研究的标准方法，对不同发育阶段的子房和果实进行固定和处理。真皮细胞含有丰富的粗面内质网和线粒体，核染色质比其他细胞稀疏。这些特征是合成蛋白质/氨基酸的细胞的典型特征，表明没有碳水化合物分泌。然而，纤维具有富含高尔基体的密集细胞质，与小泡和光滑内质网有关，这是碳水化合物分泌细胞的共同特征。我们的结果表明，真皮细胞不负责分泌植物黑色素，这与文献中以前的描述不同；相反，这个功能被分配给相邻的纤维，其组织类似于分泌碳水化合物的细胞。
