Colleters, which are glands that produce sticky secretion, have ecological and taxonomic relevance in Apocynaceae. We studied the distribution, morphology, ontogenesis, and cellular secretions of leaf colleters in Tabernaemontana catharinensis A.DC. Samples from mature embryos, seedlings, and plants were processed according to usual methods for anatomical, histochemical, and ultrastructural analyses. Colleters are non-vascularized emergences that occur on the adaxial face of expanded cotyledons, eophylls, and metaphylls and at the intrapetiolar and interpetiolar positions. Standard, bifurcate, trifurcate, and sessile colleters were found, and these glands did not differ in their ontogenesis, histochemistry, or histological composition. Golgi bodies, rough endoplasmic reticulum, and plastids filled with oil droplets were the predominant organelles in the epithelial cells. Mucilage accumulated in large periplasmic spaces, traversed the outer cell wall and the permeable cuticle, which remained intact. Senescent epithelial cells were characterized by signs of cell plasmolysis, organelle degradation, membrane vesiculation, and ruptured tonoplast. Ultrastructural changes in the cell wall strengthen the argument for the involvement of this cellular compartment in the exudates’ exit. We provide the first report of the occurrence of different types of colleters in a Rauvolfioideae member. Our ontogenetic data support the hypothesis that morphological variants are deviations from the standard type.

Premise of research. In Apocynaceae, nonarticulated laticifers have been recorded in most species studied. Interpretation of the mode of development of laticifers, whether articulated or nonarticulated, is controversial, possibly because of the rapid changes that occur in the early differentiation stages of the structures. Here, we describe laticifers in the embryo, seedling, and plant of Tabernaemontana catharinensis A.DC. (Apocynaceae), aiming to understand the structure and developmental mechanism of the laticifer system. Methodology. We prepared samples of mature embryos, 20-d-old seedlings, and 80-d-old plants of T. catharinensis according to conventional light microscopy techniques for anatomical and histochemical analysis. Pivotal results. Articulated anastomosing laticifers with intrusive growth, producing proteins, lipids, and terpenes, are present from mature embryos. Alkaloids are present in the laticifer protoplast of the older portions of the stem. Laticifers of the primary system originate from the ground meristem and procambium, and those of the secondary system originate from the vascular cambium toward the secondary phloem. In the embryo, laticifers are found in the ground meristem and procambium but do not occur in the promeristem; the nodal region exhibits lateral projections between laticifers and ground meristem cells. In seedlings and plants, laticifers are immersed in the parenchyma tissue and associated with the primary and secondary phloem of the root and shoot systems. The anatomical evidence suggests the incorporation of meristematic and parenchyma cells within the laticifer system. Conclusions. The laticifer system of T. catharinensis has a complex structure and developmental mechanism involving protoplast fusion, the addition of cells, and intrusive growth. We recorded, for the first time, the occurrence of intrusive growth associated with articulated anastomosing laticifers in a member of Apocynaceae. Our findings highlight the importance of detailed anatomical analysis to properly classify laticifers and to access their origin and development.

This study investigates the histology and subcellular features of secretory cavities during the development of the shoot apex of Metrodorea nigra A. St.-Hil. in order to better understand the functioning of these glands. This Rutaceae species is a very suitable model for studying secretory cavity life span, since the shoot apex exhibits both dormant and growth stages during its annual cycle. Shoot apices were collected during the dormant and growth stages from populations of M. nigra growing under natural conditions. Materials were processed using standard techniques for light and electron microscopy. The secretory cavities originate under the protodermis, and their initiation is restricted to the early developmental stage of shoot organs, which are protected by a hood-shaped structure. Secretory cavities have a multi-seriate epithelium surrounding a lumen that expands schizolysigenously. Oil production begins before lumen formation. When the shoot apex resumes development after the dormant stage, the glands remain active in oil secretion in the developing shoot apex and fully expanded leaves. The mature epithelial cells are flattened and exhibit very thin walls, large oil bodies, leucoplasts surrounded by endoplasmic reticulum, and mitochondria with unusual morphology. The tangential walls of the epithelial cells facing the lumen undergo continuous peeling. The vacuole extrusion appears to be the primary mode of release oil into the lumen, in an exocytotic way. The continuity of oil secretion is ensured by the replacement of the damaged inner epithelial cells by divisions in the parenchyma layer that surround the oil gland, likely a meristematic sheath.

This study aims to investigate colleters' secretory function, on cellular level, in Rubiaceae species from contrasting environments looking to explore the association between secretion and environment. We collected samples from eight species of Rubiaceae growing in forest and savanna having standard-type colleters with diverse histochemistry (hydrophilic, lipophilic and mixed secretions) and processed for both conventional and cytochemical study under transmission electron microscopy (TEM). The standard colleters, although similar in morphology and anatomy, exhibited marked differences on cellular level, especially in the abundance and topology of Golgi bodies, endoplasmic reticulum and plastids when comparing forest and savanna species. These differences were clearly aligned with the chemical nature of the secretions they produce, with predominance of hydrophilic secretions in forest species and lipophilic or mixed secretions in savanna species. The combination of methods in electron microscopy revealed the sites of synthesis and intracellular compartmentation of substances, the mechanisms of their secretion from the protoplast and confirmed the involvement of the outer walls of the epithelial cells in the elimination of exudates to the gland surface. Our study suggests a potential environment-associated plasticity of the secretory cells of standard-type colleters in modulating their secretory function performance.

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