Resin secretory canals in Protium heptaphyllum (Aubl.) Marchand. (Burseraceae): a tridimensional branched and anastomosed system

Abstract

Protium heptaphyllum is a Burseraceae species known by the production of aromatic resin with medicinal, economic, and ecological values. Information on the development, architecture, and lifetime of the secretory system are crucial to understand the resin production and contribute to a more sustainable tapping regime. We investigated the histology and ultrastructure of the secretory canals under a developmental point of view. Stem samples were analyzed under light and transmission electron microscopy by conventional and cytochemical methods. Secretory canals, originated from procambium and cambium, occurred immersed in the primary and secondary phloem. Mature canals have a secretory epithelium and a wide lumen where the exudate is accumulated. A sheath of parenchyma cells with meristematic features surrounds the epithelium. The canals originate by schizogenesis and develop by schyzolysigenesis. Canals active in secretion occurred since the shoot apex and near the cambium. In the dilation zone of the secondary phloem, secretory canals exhibit sclerified epithelial and sheath cells and are inactive in secretion. Secreting epithelial cells have subcellular apparatus consistent with oleoresin, polysaccharides, and enzymes secretion. Pectinase and cellulase were cytochemically detected in developing canals and are involved in cell wall changes associated to canal growth and release of exudate. In P. heptaphyllum, the secretory system has a complex structure resultant from longitudinal growth, lateral ramification, and fusion of the adjacent canals, in addition to intrusive growth of both epithelial and sheath cells. Although some anatomical results are already known, ultrastructural data represent the novelty of this work. Our findings can contribute to the establishment of more efficient and sustainable techniques for resin extraction in this species.

Structural and histochemical attributes of secretory ducts and cavities in leaves of four species of Calophyllaceae J. Agardh in Amazonian savannas

“…Our results show that the histochemical and TEM analyses show that the epithelium and parenchymatous sheath of ducts and cavities act as production sites of hydrophilic and lipophilic secretions. Previous studies have reported that the epithelium and parenchymatous sheath act as secretion production sites (Rodrigues et al, 2011a,b;Leite et al, 2014;Palermo et al, 2018). The ultrastructure of epithelial cells shows that the secretion is externalized to the lumen by the eccrine mechanism, corroborating the study of Leite et al (2019).…”

“…Epithelial cells with thin, disorganized walls, a winding plasma membrane, vacuolization, low-density peripheral cytoplasm with little osmiophilic material, few organelles and mitochondria and numerous vesicles adhered to the membrane are evidence that secretory cells do not present an intense secretory process, as observed in duct and cavity-secreting epithelial cells in the literature (Franco & Albiero 2018;Palermo et al, 2018;Leite et al, 2019;Haratym et al, 2020). However, our results corroborate Peng et al (2012) and Turner & Lange (2015) when describing ultrastructural characteristics of cavities in adult tissue, and in part with results of Lacchia & Carmello-Guerreiro (2009) for epithelial cells of secretory ducts of Anacardiaceae in the senescent stage.…”

“…The presence of a parenchymatous sheath surrounding the epithelial cells of the ducts and cavities plays an important role in the maintenance and replacement of non-functional cells of the epithelium (Rodrigues et al, 2011a,b;Leite et al, 2014;Palermo et al, 2018). It is important to consider the presence of ducts and cavities with collapsed epithelial cells and covered by a potentially active parenchymal sheath and rich in secretions that were observed in the histochemical tests.…”

Ontogenesis of Resin Ducts and Secretory Process in Protium spruceanum (Burseraceae) Stems

“…Throughout history, plant resins have been, among others, widely used for embalming, for religious rites and for various medical purposes (Langenheim, 2003). Emulsions, rich in terpenoids and mucilage, are produced in structures known as secretory ducts, and they play important roles in deterring herbivores and pathogens (Palermo et al, 2018). Despite advances in our knowledge concerning resin duct structure, secretory processes, and resin composition, many aspects still require in-depth investigations, especially among tropical species.…”

“…The study of distribution patterns of resiniferous ducts within those structures, which vary greatly among species, will be important for elucidating their ecological roles and defining strategies for commercial resin harvesting. Cytological evaluations, in turn, are essential for understanding the processes involved in resin production, as the cellular machinery required and the dynamics of the secretory processes are directly related to the chemical nature of the emulsions produced (Setia et al, 1977; Bhatt, 1987; Nair & Subrahmanyam, 1998; Palermo et al, 2018). Ontogenetic studies are also needed to define the structural type of the resin duct, as they can develop from lysis and/or from cell separation.…”