Silvia Rodrigues Machado

Mangrove ecosystems are frequently exposed to high concentrations of iron (Fe) in sediments, resulting in Fe accumulation in plant tissues. Although Fe is an essential micronutrient involved in several metabolic processes, its excess requires efficient mechanisms of compartmentalization and storage to maintain cellular homeostasis. Histochemical detection using the Perls reaction has usually been applied to identify ferric iron (Fe ³⁺ ) in biological tissues; however, the combination of this technique with ultrastructural and elemental analyses remains relatively unexplored in plant cells. In this study, we investigated Fe localization in leaf tissues of Rhizophora mangle L. (Rhizophoraceae), a dominant mangrove species, by combining complementary approaches, including Perls cytochemical reaction, transmission electron microscopy (TEM), scanning transmission electron microscopy coupled with high‐angle annular dark‐field imaging (STEM‐HAADF), and energy‐dispersive X‐ray spectroscopy (EDS). Perls‐positive electron‐dense deposits were visualized at the ultrastructural level, and their elemental composition was further characterized by EDS analyses. Fe‐containing deposits were detected in the epidermis, mesophyll parenchyma, mucilage cells, and vascular tissues, as well as in multiple cellular compartments, including plastids, mitochondria, vacuoles, cell walls, intercellular spaces, and plasmodesmata, whereas sclerenchyma cells showed no detectable Fe‐containing deposits. The combination of Perls reaction with TEM, STEM‐HAADF, and EDS provides a complementary approach for high‐resolution visualization and elemental characterization of Fe‐containing deposits at the subcellular level. This integrated methodology may facilitate the investigation of Fe distribution and compartmentalization in plant tissues under contrasting conditions of Fe availability.

This viewpoint highlights the importance of, and the support required for the Brazilian National Institute of Science and Technology - Virtual Herbarium of Flora and Fungi (INCT-HVFF). It started in 2009 with 25 Brazilian herbaria and three from abroad. Now, it is a network of 170 Brazilian herbaria and 27 from other countries. The INCT-HVFF makes data and images of algae, fungi, and plants from these herbaria freely and openly available through the online repository speciesLink, as well as through GBIF and SiBBr. The speciesLink is a platform developed and maintained by CRIA (Reference Center for Environmental Information), a Civil Society Organization of Public Interest that provides tools for searching and analyzing biodiversity data and makes information about Brazil’s biodiversity accessible to all interested. The focus of the INCT-HVFF, as well as of CRIA, is to provide biodiversity data, contributing directly to the conservation and sustainable use of Brazil's biological resources. Today, the INCT-HVFF shares more than 13.9 million records of algae, fungi, and plants from Brazil and neighboring countries. Adequate funding is essential to ensure that this network continues to be an important source of data, information, and knowledge, offering many benefits to its users.

Secretory cavities and canals are traditionally treated as distinct anatomical categories and widely employed as diagnostic characters in taxonomic studies. However, their coexistence or the presence of intermediate forms in the same individual or organ points to a more intricate developmental relationship. The mechanisms underlying their formation and structural differentiation, particularly the boundaries between cavities and canals, remain insufficiently understood. In this study, we selected Myrsine guianensis (Aubl.) Kuntze (Primulaceae) because it displays globose and elliptical cavities alongside linear, canal-like secretory spaces. This condition raises a fundamental question: do these structures represent two discrete types of secretory spaces, or are they transitional forms along a developmental continuum? To address this question, we investigated the secretory spaces from a developmental point of view using light and transmission electron microscopy. Secretory cavities originated from the fundamental meristem through a schizolysigenous process, giving rise to a lumen lined by a uniseriate secretory epithelium and surrounded by one or two layers of sheath cells. Epithelial cells exhibited ultrastructural features indicative of intense metabolic activity associated with oil-resin synthesis. Secretion involved pronounced cell-wall remodeling, transient periplasmic spaces, and the replacement of senescent epithelial cells. A shift from resin- and phenolic-rich secretion to predominantly oil-rich secretion coincided with epithelial senescence and the recruitment of sheath cells, thereby sustaining secretory activity. The fusion of adjacent cavities, epithelial reorganization, and progressive lumen expansion produced transitional forms between globose and elongated structures, supporting the existence of a developmental cavity-canal continuum. This structural plasticity challenges the view of secretory spaces as discrete anatomical entities and suggests that spatial constraints during morphogenesis contribute to their diversification.

Ruta graveolens L. fruits are densely covered with translucent dots corresponding to secretory cavities that accumulate bioactive metabolites, primarily essential oils. Immature fruits present an aromatic surface exudate, indicating the active release of secretory products despite the internal location of the cavities. This study investigated the origin, development, ultrastructure, and secretion-release mechanisms of fruit secretory cavities using light, scanning, and transmission electron microscopy. Secretory cavities originated from clusters of ground meristem cells associated with phloem strands. Lumen formation began with the collapse of central cells, while surrounding cells differentiated into a metabolically active secretory epithelium rich in polymorphic plastids, smooth endoplasmic reticulum, mitochondria, vesicles, and lipid bodies. Mature cavities consisted of a multilayered epithelium surrounding a large lumen and enclosed by a parenchymatous sheath. Progressive lysis of inner epithelial cells contributed to lumen expansion and secretion accumulation. As cavities enlarged, they became positioned immediately beneath the epidermis, whose cells became compressed and flattened. Secretion was released through the rupture of glandular and epidermal cells and through stomata located in epicarp depressions. Ultrastructural evidence indicates the combined operation of eccrine, granulocrine, and holocrine secretion mechanisms. Pectin–cellulosic wall thickenings likely function as apoplastic barriers, directing secretion toward the lumen and protecting adjacent tissues.

This study presents the comparative, function-oriented analysis of petal structure and osmophore distribution in three Malpighiaceae species, complementing the established role of calyx elaiophores. Integrating light and electron microscopy with floral biology observations and visitor records, the authors document interspecific variation across core floral traits: anthesis timing; corolla senescence, color, and dimensions; petal micromorphology; and the spatial organization of scent-emitting areas. Byrsonima coccolobifolia possesses flat, textured petal surfaces without glands; scent is emitted from a lobed, striated basal outer region whose cells accumulate starch prior to anthesis, indicating metabolic provisioning. In contrast, Banisteriopsis variabilis and Peixotoa reticulata share rough petal surfaces but differ in epidermal cell shape—cone-shaped in B. variabilis versus rounded in P. reticulata . Both species display enlarged intercellular spaces and minute, vascularized scent glands along fimbriate petal margins that exhibit subcellular traits diagnostic of osmophores, supporting their role in volatile biosynthesis and release. Across the three focal taxa, the findings resolve two principal scent-emission strategies: a diffuse basal emission zone ( B. coccolobifolia ) versus discrete marginal osmophores ( B. variabilis , P. reticulata ). Functionally, petal surface architecture and mesophyll organization likely enhance visual signaling, while osmophores are central to attracting oil-collecting bees. Under an evolutionary framework, the evidence indicates ongoing specialization of floral tissues for scent production, with probable effects on pollinator attraction and specificity. The study thus refines our understanding of multimodal floral signaling in Malpighiaceae and suggests that diversification in petal anatomy and osmophore placement may shape plant–pollinator interactions and the evolution of pollination systems within the family.

The Zinc Iodide‐Osmium Tetroxide method (ZIO) is recognized for its effectiveness in impregnating the endomembrane system, particularly Golgi bodies. Nevertheless, its application in plant cell studies remains limited. This research focuses on Palicourea rigida Kunth, a Rubiaceae species known for its colleters producing a mixed secretion primarily composed of lipophilic substances. The aim of our study was to assess the effectiveness of the ZIO method in investigating ultrastructural variations of epithelial cells during the secretory phase. Samples were fixed for 12 h in a solution containing 2.5% glutaraldehyde and 4% paraformaldehyde in 0.1 mol/L phosphate buffer at pH 7.3. This was followed by a 22‐h incubation at 4°C in a solution that included zinc (Zn), resublimed iodine (I), TRIS‐aminomethane, and osmium tetroxide (OsO ₄ ). Subsequently, the samples underwent dehydration through a graded series of acetone and were embedded in Araldite resin. Ultrathin sections were contrasted with uranyl acetate and lead citrate and analyzed using a transmission electron microscope at 60 kV. While the epithelial cells exhibited morphological similarities, the ZIO method revealed diversity in their endomembrane systems. Some cells were rich in rough endoplasmic reticulum (RER), while others were abundant in smooth endoplasmic reticulum (SER), and some primarily contained Golgi bodies. These findings underscore the division of labor among neighboring secretory cells, which, despite their morphological similarities, show differences in their endomembrane systems during the same secretion stage. Therefore, the ZIO method emerges as a promising tool in plant secretion research, contributing to the understanding of the functional diversity of the endomembrane system in plant glands.

Nectaries are specialized nectar-producing structures. Nectar traits affect animal behaviour and ecological and evolutionary processes, such as pollination and biotic defence. Previously, we found that there are differences in the characteristics of nuptial nectar (NN) and extranuptial nectar (ENN) and in the types of animals that visit each nectary in Amphilophium mansoanum (Bignoniaceae) flowers. We now hypothesize that nectar traits reflect the anatomical, histochemical, and subcellular characteristics of each nectary type. Using routine light microscopy, scanning electron microscopy, and transmission electron microscopy methods, we studied NN and ENN, respectively in young flower buds, pre-anthesis buds, and first- and second-day flowers. NN was a prominent annular disk; whereas, ENN was a concave, patelliform trichome. Only ENN contained alkaloids, while both nectaries contained starch grains, lipid droplets, proteins, terpenes, and phenolic compounds. Both nectaries showed subcellular organization consistent with hydrophilic and lipophilic secretion, the latter being predominant in second-day flowers. In NN, the subnectary parenchyma had phloem and amyloplasts until pre-anthesis. Starch grains decreased and tracheary elements were seen in newly opened flowers. ENN are not vascularized, with vascular bundles from the calyx approaching the base of the nectary. Starch grains were scarce and very small in the ENN secretory head cells. Fibrillary proteins were found only in NN and periplastidial reticulum was observed only in ENN. In NN, nectar secretion begins shortly before anthesis, being released through the raised stomata and the reticulate cuticle. In ENN, secretion extends from the young flower bud stage to senescent flowers, accumulating in small subcuticular spaces and being continuously released through the intact cuticle. Temporal differences in NN and ENN production, as well as in the structural characteristics and nectar release mechanisms between NN and ENN, may explain the differences in nectar characteristics of A. mansoanum.