Yve Canaveze

Secretory cavities in Myrtaceae typically store lipophilic substances involved in plant defense. However, their structural and functional reorganization during gall development remains poorly understood, particularly regarding how gall complexity and biotic interactions influence these changes. Here, we analyzed the anatomical, histometric, and histochemical features of secretory cavities across eight gall morphotypes induced on three Eugenia species ( E. astringens , E. copacabanensis , and E. uniflora ). We hypothesized that gall induction modifies secretory cavities, which may result in functional alterations during cecidogenesis, and that the magnitude of these alterations relates to gall structural complexity. Across most morphotypes, we observed a suppression of cavities near the larval chamber and reduced secretory cavity density in gall wall, an integrated strategy that likely minimizes the inducer’s exposure to secondary metabolites. Conversely, in E. astringens fusiform galls, an associated fungal symbiont indicates that these are ambrosia galls. In these galls, we recorded higher cavity density, larger lumen area, and phenolic accumulation, suggesting a repurposing of these structures to maintain a microenvironment favorable to the fungal-insect association. The results partially supported our hypothesis: while gall complexity correlated with cavity reorganization in E. astringens , this pattern was inconsistent in the other host species, indicating that taxonomic identity, morphogenetic constraints, and biotic interactions also contribute to these traits. These findings demonstrate that secretory cavity reorganization is not a uniform process but a highly plastic response, revealing diverse functional trajectories that range from structural reduction to chemical enhancement, depending on the specific host plant-gall inducer system.

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.

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.

Throughout evolutionary time, florivory has always represented an important source of selective pressure on flower evolution. When feeding, florivores remove corolla portions and undoubtedly change floral visual traits; however, we are in the early stages of understanding the effects of florivory on floral olfactory signalling. Florivores may jeopardize floral scent emission by feeding on flower parts responsible for volatile synthesis/emission, or by inducing plant physiological responses that alter floral scent. Thus, after florivory, flowers may no longer attract pollinators or might even repel them due to local short‐term changes in floral scent emission. Here, we investigate whether damage by florivores alters the amount and composition of floral scent. We describe natural florivory patterns and anatomically characterize the corolla portions potentially involved in scent emission in seven plant species pollinated by bees, hummingbirds, hawkmoths, or butterflies, which have diverse florivores, in a neotropical savanna. Moreover, we performed natural experiments to test whether florivory leads to short‐term local changes in floral scent phenotype. We found that even when florivores consumed 15% of the corolla portions with anatomical scent‐emitting features, there was no reduction in total amount of floral scent, except in a hawkmoth‐pollinated species, which showed a reduction in scent emission although only 3% of the osmophore‐bearing areas were consumed. Florivory did not affect scent composition in any species. Our data suggest a stability in post‐florivory scent emission, which may guarantee the maintenance of pollinator visitation regardless of florivory, indicating a resilience of natural systems with multiple and simultaneous interactions.

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.

Floral glands, which produce diverse metabolites, have become the focus of increasing interest because of their important roles in plant-animal interactions. The glands in the receptacle of Pseudobombax longiflorum (Malvaceae) are widely accepted as nectaries. Using light, scanning, and transmission electron microscopy, we studied the anatomy, histochemistry, ultrastructure, and secretory dynamics of the receptacle glands in this species. The glands were active in secretion from young flower buds to immature fruits. Trigona spinipes was the most abundant and frequent visitor. The glands were composed of a uniseriate epidermis covered with a thick cuticle and a multilayered parenchyma, exhibiting two subregions with abundant phloem in the innermost region. These glands produced sugars, resins, oils, and phenolic compounds. Glandular cells exhibited large nuclei with nucleoli, polymorphic plastids with lipophilic inclusions, numerous mitochondria, endoplasmic reticulum profiles, cytoplasmic oil bodies, and vacuoles containing phenolic compounds. Plasmodesmata indicate that secretory components are transported from cell to cell via the symplast. There is also evidence for granulocrine and eccrine secretion mechanisms. The accumulated secretions form a bulge in the central region of the gland. The bulged epidermis detached from the parenchyma cells, and the rupture of the epidermal cells released the accumulated hydrophilic components. Residual lipophilic secretions were embedded in the epidermal cell wall and cuticle. The receptacle glands of P. longiflorum are not typical nectaries but mixed glands that produce both hydrophilic and lipophilic secretions during floral development until young fruits.

The gall-host Eugenia uniflora (Myrtaceae) is adaptable to different light conditions, enabling leaf production and survival in both sun and shade. Leaves of E. uniflora in shaded environments have more mesophyll layers, and galls of Clinodiplosis profusa (Cecidomyiidae) are larger and wider. Based on these previous observations, this study investigated the morphogenesis of galls induced by C. profusa on leaves of E. uniflora in different light conditions, revealing if the galls have a potential for acclimation, as observed with leaves. For this purpose, we compared the anatomical, histometric, and histochemical development of leaves and galls at different stages of development in sun and shade environments. Additionally, we analyzed the cytological features of the tissues composing the mature gall walls. Cells of shade galls expanded more toward the end of the developmental phase, which may explain the larger volume found for shade galls in a previous study. However, during the mature phase, these galls showed no significant differences in tissue thickness and final cell elongation in the contrasting light conditions. In the ultrastructural analyses, mature galls showed a gradient distinguishing the outer and inner parenchyma cells. The inner parenchyma had nutritive cells, with dense cytoplasm and abundant organelles. A higher accumulation of starch grains in nutritive cells, with evidence of hydrolysis of starch grains detected in the innermost layers leads to the accumulation of reducing sugars, which, with the presence of plastoglobules and protein bodies, are important mechanisms of oxidative stress dissipation in the cells in contact with the gall inducer.