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TEM image of material postfixed in osmium tetroxide, embedded in SPI 812, and viewed in transverse section. Shown are the proximal ends of two epidermal cells (ec) bordering three mesophyll cells (mc) and associated intercellular spaces (is). Thickenings of Igersheim (ti) are restricted to the walls of the inner tangential walls of the epidermal cells; the thickenings may affect only certain parts of the wall. Note single plasmodesma (pd) (compare Figure 10) in the thickening of Igersheim. Vacuoles of mesophyll cells filled with numerous osmiophilic droplets.
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Secondary pollen presentation is a well-known phenomenon in the Rubiaceae with particularly conspicuous pollen presenters occurring in the tribe Vanguerieae. These knob-like structures are formed by a modification of the upper portion of the style and stigma, together known as the stylar head complex. In the flower bud and shortly before anthesis,...
Citations
... Rutaceae ( Darrault and Schlindwein 2005;Araújo et al. 2011Araújo et al. , 2014Koptur et al. 2020;Ramos et al. 2022 Loganiaceae (13) 2 Style Deposition Endress et al. 1998;Erbar and Leins 1999;Shotts 2021 Rubiaceae (614) 38 Style Deposition Nilsson et al. 1990;Yeo 1993;Imbert and Richards 1993;Igersheim 1993;Ladd 1994;Puff et al. 1996;Block and Igersheim 2001;Lin et al. 2012;Tilney et al. 2014;Xu et al. 2022;Romero et al. 2022 Lamiales: ...
... It is mentioned for the first time here in Cordiera, Genipa, Randia, and Tocoyena. In Vangueria infausta (tribe Vanguerieae, Rubiaceae) an association has been found between the outstanding oncus and the cellular structure of the epidermal stigmata that would facilitate the secondary presentation of pollen thanks to the connections provided by the protruding onci between the pollen grain and the epidermis of the pollen presenter (Tilney et al. 2014). Considering that the species analysed have a secondary presentation of pollen, future ultrastructural and histochemical studies of stigma and pollen may reveal whether a similar relationship exists. ...
we conducted anatomical analysis of anthers with the aim to establish the differences in the development pattern of microsporophytes and microgametophytes between perfect and imperfect flowers in the tribe Gardenieae (Rubiaceae). The species studied were: Tocoyena formosa (monoecious with perfect flowers), Cordiera concolor, Genipa americana, Randia calycina, and Randia heteromera (dioecious with imperfect flowers). Flowers in successive stages of development were collected and fixed. The material was processed and examined using light microscopy and scanning electron microscopy. The present study revealed the stage when pollen is arrested in the functionally pistillate flowers of the dioecious taxa. Based on these observations an evolutionary sequence of changes towards the reduction of non-functional anthers in Rubiaceae is proposed. In addition, we describe and discuss characters that might be of importance in future phylogenetic studies in Rubiaceae (e.g., pollen morphology and its dispersal unit, the presence of orbicules, and a new type of placentoid).
... Thickening in the epidermal cells of the stigma, as described for C. glabratus (in this study) and C. occidentalis (Imbert and Richards 1993), was also observed in Vangueria infausta and it was called "Igersheim thickening," which would be related to the secondary presentation of pollen (SPP) (Tilney et al. 2014). However, in C. glabratus, this type of thickening is found in both the PF and SF, which could suggest that there is no association with SPP, since the PF lacks this mechanism due to abortion of the pollen grains. ...
... This is a common characteristic in Rubiaceae (Tilney et al. 2014) and it can occur in protandric flowers, both perfect and staminate flowers, in which the pollen grain is deposited on the style, stigmas, or on both (Puff et al. 1996). In the tribe Naucleeae, the SPP represents a synapomorph (Manns and Bremer 2010) and was described in C. occidentalis (Meehan 1887;Imbert and Richards 1993), in Nauclea subdita (Burck 1884), in Neonauclea pallida, Uncaria cf lanosa, and in Sarcocephalus latifolius (Puff et al. 1996). ...
Information on the reproductive anatomy in genera of the tribe Naucleeae, particularly Cephalanthus, is scarce and fragmented. Of the six species in the genus, only the mature megagamethophyte of Cephalanthus occidentalis has been described. This study aims to provide information on embryological aspects in flowers of C. glabratus and to analyze the morphology and anatomy of the flowers, fruit, and seed in the six species of the genus. Cephalanthus glabratus have imperfect flowers: pistillate (PF) and staminate (SF). In the PF, the ovules are functional, while in the SF, they atrophy during the formation of the embryo sac. The mature ovule has a single integument, corresponds to the Phyllis type and the embryo sac is a Polygonum type, forming only in the PF. The presence of pollenkitt and secondary presentation of pollen were observed in the SF, as well as in the pollen formation previously described, whereas in the PF, they are absent, due to the collapse of the pollen grains inside the indehiscent anthers. The analysis of the ontogeny of the ovular excrescence in C. glabratus determined its funicular origin, calling it an aril. Its development is a pre-anthesis event, initiated during megasporogenesis. In seeds, the aril is a fleshy, white appendage which almost completely envelops the seeds of Cephalanthus, except for Cephalanthus natalensis where it is noticeably more reduced. Studies of the fruit in Cephalanthus species indicate that the infructescence is a dry schizocarp which separates into uni-seminated mericarps, except in C. natalensis that has fleshy indehiscent fruit.
... In the non-acetolyzed grains of I. laevis, the protrusion of oncus has been observed in each aperture, which is a structure composed of intine and protoplast (Hyde 1955). The presence of oncus in pollen grains has been reported in other angiosperms (Hyde 1955;Tilney and Van Wyk 1997) and even in other species of Rubiaceae from different tribes (Tilney et al. 2014;Yue et al. 2017;Romero et al. 2017;Judkevich et al. 2020b), and their function is still not clarified. ...
In this study, we performed an anatomical analysis of the polysporangiate anthers and the development of pollen in Isertia laevis (Rubiaceae) with the aim to elucidate the internal structure of these atypical anthers. For this purpose, flowers in successive stages of development were dissected and the anthers were processed for conventional anatomical analysis. The material was examined using light microscopy and scanning electron microscopy. The present study shows that the anthers of Isertia laevis have two thecae divided into multiple microsporangia. This division is due to the presence of transverse and longitudinal septa formed of parenchyma and idioblasts with crystals. The septa appear together with the microsporangia and remain in the mature anther, even developing fibrous thickening. As the anther matures, the idioblasts in the septa accumulate crystals until they break, facilitating the separation of the septa from the outer wall of the theca, and thus apparently assisting the process of dehiscence. The mature anther opens through the longitudinal dehiscence of each theca. In addition to the anatomy of the anther, the development and morphology of the pollen, and the presence of orbicules are described. The structure of the anthers of I. laevis is discussed with other polysporangiate species in the Rubiaceae and angiosperms.
... These cells resemble unicellular trichomes or papillose cells, which are highly variable epidermal appendages, whose distinction is not always clear (Evert 2006;Rudall 2007). Another feature that distinguishes these cells is their remarkably dense cytoplasm, which might be rich in organelles, as commonly observed in cells with active physiological roles in the secretion of secondary metabolites (Fahn 1979;Evert 2006;Tilney et al. 2014;Fernandes et al. 2017;Ballego-Campos & Paiva 2018). Also, the histochemical detection of proteins in the cytoplasm of the secretory rings may also indicate high metabolic activity within these cells (Fernandes et al. 2017). ...
... It may also be a self-sealing mechanism, that is, to protect plants from dehydration and infections after damage by sealing wounds (Anandan et al. 2018). In any case, it has been accepted that the capacity in storage and water retention of epidermal cells may be determined by the amount and composition of pectins in thickened walls (Voragen et al. 2009;Kuster et al. 2018), as seen in Anulocaulis and indicated for similar epidermal cells in secondary pollen presenting structures as observed in Vangueria infausta (Rubiaceae) (Tilney et al. 2014). Besides the similarity in shape, the epidermal cells in V. infausta were also reported with a cytoplasm rich in organelles, including secretory vesicles that might be involved in the production of hydrophilic and sticky substances (Tilney et al. 2014). ...
... In any case, it has been accepted that the capacity in storage and water retention of epidermal cells may be determined by the amount and composition of pectins in thickened walls (Voragen et al. 2009;Kuster et al. 2018), as seen in Anulocaulis and indicated for similar epidermal cells in secondary pollen presenting structures as observed in Vangueria infausta (Rubiaceae) (Tilney et al. 2014). Besides the similarity in shape, the epidermal cells in V. infausta were also reported with a cytoplasm rich in organelles, including secretory vesicles that might be involved in the production of hydrophilic and sticky substances (Tilney et al. 2014). McClellan and Boecklen (1993) experimentally examined the role of the secretory rings in Boerhavia spicata and determined that such structures appear to discourage ant-aphid colonization or reduce ant or aphid density. ...
Anulocaulis, commonly known as “ringstem,” is a small, unusual genus restricted to the Chihuahuan, Sonoran, and Mojave deserts of North
America. Here we combined light microscopy and histochemical tests to characterize for the first time the “sticky structures” (here called
secretory rings) found on the stem internodes of Anulocaulis. The secretory rings were shown to be groups of epidermal cells, or unicellular glandular trichomes, which largely differ from their neighboring cells both in structure and histochemistry. The cells start to differentiate in early stages of stem development. They begin as regular epidermal cells, but later their anticlinal and external tangential walls start to enlarge. At maturity the cells become remarkably elongated, even balloon-like, with dense cytoplasmic content. Although the secretory rings have been reported as “mucilaginous structures” based on morphological observations, preliminary histochemical analyses showed that its exudate is complex, including a mixture of mucilage, proteins, and phenolic compounds. Future investigations are needed to compare the anatomy of the secretory rings within related genera of Nyctaginaceae and characterize the chemical components of their exudate more specifically to search for potential homologies and adaptive functions of these structures.
... Robyns (1928) published the first monograph of Vanguerieae, which included the description of Eriosemopsis. Its inclusion in the tribe is supported by several morphological characters, not least its conspicuous stylar head complex, a structure that is diagnostic for Vanguerieae (Igersheim, 1993;Tilney, Van Wyk & Van der Merwe, 2014). ...
The taxonomic status and phylogenetic position of three pyrogenic geofrutex members of Rubiaceae confined to grassland or savannah in central and southern Africa are clarified. Eriosemopsis, represented by E. subanisophylla, is a monotypic genus endemic to South Africa. Although morphologically clearly a member of tribe Vanguerieae (Rubiaceae), its exact phylogenetic placement was hitherto unknown. Using five molecular markers, we confirmed the separate generic status of Eriosemopsis and demonstrated that it is part of the Canthium group, closely related to Pygmaeothamnus chamaedendrum. This last species is shown not to be closely related to Pygmaeothamnus zey-heri, the type species of Pygmaeothamnus, and is therefore transferred to a new monotypic genus, namely Bridsonia. Recognition of Bridsonia chamaedendrum also renders Pygmaeothamnus monotypic. Illustrations of all three species involved and a distribution map for B. chamaedendrum are provided.
... Importantly, Auramine O also showed broader staining in the upper part of the root, suggesting that it also has the ability to bind to suberin or suberin-like com- pounds ( Figure 4d). As Auramine O has been reported to stain exine-like molecules and cutin (Edlund et al., 2004;Nishikawa et al., 2005;Tilney et al., 2014;Yadav et al., 2014;Gimenez et al., 2015;Li et al., 2016), our observation supports the idea that Arabidopsis cutin and suberin are very similar in structure and that Auramine O could indis- criminately bind both compounds. Besides Basic Fuchsin and Auramine O, we tested Safranine O as a potential lig- nin stain (Sibout et al., 2005;Ramirez et al., 2011). ...
Higher plant function is contingent upon the complex three-dimensional architecture of their tissues, yet severe light scattering renders deep, 3D tissue imaging very problematic. Although efforts to “clear” tissues have been ongoing for over a century, many innovations were made in recent years. Among them, a protocol called ClearSee efficiently clears tissues and diminishes chlorophyll autofluorescence, while maintaining fluorescent proteins - thereby allowing analysis of gene expression and protein localisation in cleared samples. To further increase the protocol's usefulness, we developed a ClearSee-based toolbox in which a number of classical histological stains for lignin, suberin and other cell wall components could be used in conjunction with fluorescent reporter lines. We found that a number of classical dyes are highly soluble in ClearSee solution, allowing to enormously simplify old staining protocols, which, additionally, have been unsuitable for co-visualization with fluorescent markers due to harsh fixation and clearing. Consecutive staining with several dyes allows 3D co-visualisation of distinct cell wall modifications with fluorescent proteins - used as transcriptional reporter or protein localisation tools - deep within tissues. Moreover, the protocol is easily applied on hand sections of different organs. In combination with confocal microscopy, this improves image quality, while decreasing time and cost of embedding/sectioning. It thus provides a low-cost, efficient method to study thick plant tissues which are usually cumbersome to visualise. Our ClearSee-adapted protocols significantly improve and speed-up anatomical and developmental investigations in numerous plant species, which we hope will contribute to new discoveries in many areas of plant research.
