Abstract Annatto (Bixa orellana L.) is the only species that produces bixin, a red pigment extracted from its seeds and used as a natural dye. Little is known about the distribution and the anatomical and ultrastructural aspects of the glands that secrete and accumulate these carotenoid pigments, considered as an idioblast. We used light and transmission as well as scanning electron microscopy to examine the ontogeny and secretory process of pigment glands in vegetative and reproductive organs of annatto. The pigment glands are distributed throughout the plant body and their development and ultrastructural aspects are similar, except in the primary roots, where only exodermal cells secrete pigment. An initial cell with conspicuous nucleus and dense cytoplasm with chromoplast, gradually coalesce with adjacent cells and only shared cell walls are degraded. The developing pigment gland becomes plurinucleated, with a single chloroplast-rich cytoplasm delimiting a large central vacuole where the secretion accumulates. It becomes a syncytium and the integrity and functionality of the protoplast is maintained until the end of the gland development. The carotenoid synthesis begins inside chromoplasts surrounded by endoplamic reticulum. The lipid content of the plastoglobuli is discharged into small vacuoles that join to the central vacuole or are discharged directly into the central vacuole. Despite the unusual shape of the annatto pigment gland, it shares the main ontogenetic characteristics with anastomosed articulated laticifer than with any other secretory structure. Our results contribute to the understanding of the annatto pigment glands and their secretion, which can be considered as anastomosed articulated laticifers that produce reddish latex, rich in carotenoids. This is the first record that demonstrates laticifers in the Bixaceae family.

中文翻译：

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红木 (Bixa orellana L.) 色素腺的合胞体发育：一种奇怪的吻合关节乳管

摘要 红木 (Bixa orellana L.) 是唯一能产生红木红的物种，红木是一种从其种子中提取的红色素，用作天然染料。对分泌和积累这些类胡萝卜素色素的腺体的分布、解剖学和超微结构方面知之甚少，被认为是一种特异母细胞。我们使用光和透射以及扫描电子显微镜检查了胭脂树营养和生殖器官中色素腺体的个体发育和分泌过程。色素腺分布在整个植物体中，它们的发育和超微结构方面是相似的，除了在初级根中，只有外胚层细胞分泌色素。初始细胞具有明显的细胞核和致密的细胞质，带有有色体，逐渐与相邻的细胞合并，只有共享的细胞壁被降解。发育中的色素腺变成多核，单个富含叶绿体的细胞质界定了一个大的中央液泡，分泌物聚集在那里。它变成合胞体，原生质体的完整性和功能性一直保持到腺体发育结束。类胡萝卜素的合成开始于被内质网包围的有色体内部。质体球的脂质成分被排放到与中央液泡相连的小液泡中或直接排放到中央液泡中。尽管胭脂树色素腺体的形状不寻常，但与其他任何分泌结构相比，它与吻合关节乳突具有主要的个体发育特征。我们的研究结果有助于理解胭脂树色素腺及其分泌，这些腺体可以被认为是吻合的关节乳管，产生红色乳胶，富含类胡萝卜素。这是在 Bixaceae 科中展示乳母的第一个记录。