Syncytial development of annatto (Bixa orellana L.) pigment gland: A curious type of anastomosed articulated laticifer

• Published in: Flora. Morphologie, Geobotanik, Oekophysiologie Vol. 274; p. 151727
• Main Authors: Almeida, Andrea Lanna, Freitas, Patrícia França de, Ferreira, Clébio Pereira, Ventrella, Marília Contin
• Format: Journal Article
• Language: English
• Published: Elsevier GmbH 01-01-2021
• Subjects: Bixin; Chromoplast; Dye gland; Laticifer; Secretion; Syncytium; Chromoplast; Dye gland; Syncytium; Laticifer; Bixin; Secretion
• ISSN: 0367-2530; 1618-0585
• DOI: 10.1016/j.flora.2020.151727

•The pigment glands are distributed in all vegetative and reproductive organs.•Annatto pigment gland has syncytial development.•Annatto pigment gland is a anastomosed articulated laticifer.•Chromoplasts and ER are the main organelles involved in secretion process.•This is the first record that demonstrates laticifers in the Bixaceae family.
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 chromoplasts gradually coalesce with adjacent cells and only shared cell walls are degraded. The developing pigment gland becomes plurinucleated, with a single chromoplast-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.