Ontogenesis secretion and senescence of Tocoyena bullata (Vell.) Mart. (Rubiacaeae) colleters

Colleters are secretory structure present on many families including Rubiaceae. Particular characteristics have been described about colleters secretory cells, however senescence process are still under debate. Tocoyena bullata (Vell.) Mart. (Rubiaceae) shoot apex were collected at Jardim Botânico do Rio de Janeiro, RJ/Brazil. Stipules were separated and fragments were fixed in 2.5% glutaraldehyde and 4.0% formaldehyde in 0.05 m sodium cacodylate buffer, pH 7.2, post fixed in 1.0% osmium tetroxide in the same buffer, dehydrated in acetone, critical‐point‐drying, sputtered coated and observed. For light microscopy fragments were fixed and dehydrated, infiltrated with historesin and stained with 1% toluidine blue. For transmission electron microscopy, the samples were infiltrated with Epoxi resin. Colleters are present on stipule adaxial surface. On the beginning of development, these structures are recognized as small projections. Later on, colleters differentiated and secrete by cuticle rupture. The colleters senescence occurs in a concomitant and indissoluble way of programmed cell death. Ultrastructural analyses during the process strongly suggest the senescence is based on a non‐autolitic programmed cell death. T. bullata colleters, present at stipule abaxial surface are cylindrical secretory structures. Colleters secretory cells originated as stipule projections; differentiate; secrete and senesce by programmed cell death. The secretion and the cell dead occurs in a concomitantly and indissoluble way.     

The structure of colleters in several species of Simira (Rubiaceae)

BACKGROUND AND AIMS: Colleters are secretory structures consisting of a parenchymatic middle axis surrounded by a layer of palisade-like epidermal cells. Colleters occur in a large number of rubiaceous species. Their function is to protect the developing shoot apex. They are also taxonomically useful in the Rubiaceae. This study characterized the structure of the colleters of Simira glaziovii, S. pikia and S. rubra and the biochemistry of secretions in S. glaziovii. METHODS: Stipules of the shoot apices of the three species studied were collected at Barragem de Saracuruna, in Rio de Janeiro state, Brazil. The samples were fixed according to the usual methods for light and electron microscopy. Secretion stipules of S. glaziovii were washed with 0.1 m Tris-HCl plus 0.1 %Triton X-100 to extract proteins and carbohydrates. KEY RESULTS: Colleters in these species are located at the base of the stipule. Each species shows a different pattern of distribution. They form as emergentia from the stipules. Simira glaziovii was different from the other two species because it exhibited vascular traces. The epidermal cells of colleters have dense cytoplasm, nuclei, small vacuoles, endoplasmic reticulum, Golgi apparatus, mitochondria and extraplasmic spaces if they are secretory. The outer cell wall of the mature colleters differs from the outer cell wall of stipule cells and immature colleters. Both carbohydrates and proteins were found in secretions from the stipules of S. glaziovii. CONCLUSIONS: Few ultrastructural differences were noted among the three species. These secretory structures not only protect the shoot apex, but also have taxonomic importance below the genus level.     

Comparative systematic study of colleters and stipules of Rhizophoraceae with implications for adaptation to challenging environments

Colleters are multicellular secretory structures found on various organs in flowering plants. Colleters on the adaxial sides of stipules have been hypothesized to play a role in protecting the developing shoot. Rhizophoraceae is a stipulate family with a broad distribution from mangrove to montane environments, which makes the family well suited for the examination of this hypothesis, but the colleters of Rhizophoraceae are not well known. We compared species from all three tribes of Rhizophoraceae, including five inland genera and all four mangrove genera. In all species, several to hundreds of colleters, sessile or stalked, arranged in rows aggregated in genus‐specific shapes, are found at the adaxial bases of open and closed stipules. Pellacalyx uniquely has additional colleters at the stipule margins. Colleters are all of the standard type, comprising a central axis of core parenchyma with large vacuoles and tannins, and an outer palisade‐like epidermis with organelles involved in secretory activity. An exception is Pellacalyx axillaris, in which colleters appear as extremely small epidermal protrusions. Kandelia obovata has a tracheary element in some colleters. Pellacalyx uniquely has an unusual fleshy outgrowth on the adaxial stipule base. We propose an evolutionary sequence in which Macarisia has plesiomorphic stipule and colleter traits and the mangrove Kandelia obovata with colleter vascular traces is most derived. Colleter and stipule structures are largely concordant with habitat and phylogeny, and show taxonomic value. The strong alignment of colleter and stipule patterns with habitat is suggestive that colleters have a protective function, although some components of these patterns may be phylogenetically determined. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 172 , 449–464.     

Colleter types in Rubiaceae, especially in relation to the bacterial leaf nodule symbiosis

Vegetative buds were removed from herbarium specimens, and a small number of living plants, of 116 species of 111 genera of Rubiaceae and processed for light-microscopic examination of colleter form and anatomy. The results were combined with those of earlier studies. Most colleters in this family are of the 'standard type' described by others. Colleters are, however, lacking in eight genera. dendroid colleters occur in six genera. Two other genera have an intermediate type of colleter. Three genera have bacterial leaf nodules; dendroid colleters are not restricted to these genera, but their pattern of occurrence suggests a causal relationship between bacterial infection and evolution of dendroid colleters. Coupled with the geographic distribution of nodulared species within these genera, this pattern indicates that Pavetta became infected very early in its evolutionary history, Psychotria relatively later, and Neorosea most recently.     

Ontogenesis, structure and ultrastructure of Hymenaea stigonocarpa (Fabaceae: Caesalpinioideae) colleters

The genus Hymenaea is characterized by a great diversity of secretory structures, but there are no reports of colleters yet. The objectives of this study are to report the occurrence and describe the origin and structure of colleters in Hymenaea stigonocarpa Mart. ex Hayne. Shoot apex samples were collected, fixed, and processed for light microscopy, scanning electron microscopy, and transmission electron microscopy as per usual methods. Colleters occur predominantly on the stipule's adaxial side. These structures are found at the base on a narrow strip, corresponding to the median vein up to half the length of the stipule. When present on the abaxial side, they are concentrated at the base and restricted to the margins. Colleters develop from the protoderm; they are elongate and club-shaped. Their body has no stratification; their surface cells differ from the inner cells only in position and presence of cuticle. Colleter cells have thin walls, dense cytoplasm, large nuclei, many mitochondria, rough endoplasmic reticulum, and abundant dictyosomes. Histochemical tests with Ruthenium red showed pectic compounds in the cytosol. In H. stigonocarpa, colleter arrangement is compatible with the hypothesis that they protect shoot apex. In this species, protection is reinforced by the sheath formed by the stipule pairs.     

Colleters in Bathysa nicholsonii K. Schum. (Rubiaceae): ultrastructure, secretion protein composition, and antifungal activity

Colleters are secretory structures well distributed in many organs of Angiosperms. Ultrastructurally, the colleters secretory cell presents an enhanced endoplasmic reticulum, Golgi apparatus, and mitochondria. Secretion synthesis, transportation, and passage through outer cell wall is poorly characterized. This study characterized the anatomy and ultrastructure of BATHYSA NICHOLSONII (Rubiaceae) colleters and evaluated the presence of protein in the secretion and its antifungal property. Samples were collected and prepared according to usual techniques in light and electron microscopy, electrophoresis, and fungal growth inhibition assay. Colleters are of a standard type, cylindrical and elongated, formed by one secretory epidermal palisade layer, and a central axis formed by parenchymatic cells and a vascular trace. Epidermal cells have dense cytoplasm with abundant ribosome, a nucleus, enhanced endoplasmic reticulum and Golgi apparatus. The outer cell wall presented morphologically distinct layers. The presence of secretory cavities was noted in all outer cell wall extents. Secretion preparations analyzed by SDS-PAGE showed that B. NICHOLSONII secretion is a mixture of proteins with molecular masses covering a range of approximately 66 to 24 kDa. This preparation presented an inhibitory effect on the fungi spore growth.     

Colleter morphology in Pavetta, Neorosea and Tricalysia (Rubiaceae) and its relationship to the bacterial leaf nodule symbiosis

Buds removed from herbarium specimens were processed for light microscopic examination of colleter form and anatomy. Most Pavetta species have dendroid colleters and bacterial leaf nodules, a correlation also found in an earlier study of Psychotria. Colleters of Neorosea , another genus with leaf-nodulated species, are more like the standard rubiaceous type that predominates in the family except that they have irregular, bulging epidermal cells. Tricalysia , a nodule-free genus closely related to Neorosea , shows a range of colleter form from standard to dendroid, and some species have the Neorosea type of colleter. Such morphological correlation between the bacterial leaf nodule symbiosis in Pavetta and Psychotria and dendroid colleters may indicate a chemical change in colleter secretion. Apart from their involvement with the bacterial symbiosis, rubiaceous colleters have now been shown to vary sufficiently in certain taxa to be considered as additional useful taxonomic characters.     

Leaf colleters in Tontelea micrantha (Celastraceae,Salacioideae): Ecological,morphological and structural aspects

The colleter secretion can be useful to protect plants of Cerrado (Brazilian savanna) biome during the long and pronounced dry season. This study describes the presence of colleters in Tontelea micrantha and represents the first record of these structures in Celastraceae. To investigate colleter structure and their secretory processes, young leaves were collected, fixed, and processed according to conventional techniques for light, and electron microscopy. Colleters were observed at the marginal teeth on the leaf. They produce mucilaginous secretions that spread over the leaf surface. After secretory phase, colleters abscise. The secretory epithelium is uniseriate and composed of elongated cells whose dense cytoplasm is rich in organelles. The ultrastructure of the secretory cells is compatible with the pectin-rich secretion. Observations of the young leaves surface revealed the presence of superficial hydrophilic secretion films that appeared to have the function of maintaining the water status of those organs.     

Floral character states of the Northeast and Tropical East African Swertia species (Gentianaceae)

The floral gross morphological and anatomical character states of 23 African Swertia species are described. Colleters are frequent in Swertia, especially at the lower rim of calyx lobes and are usually placed in a single row except in S. crassiuscula (they are not "typical" colleters). The aestivation of corolla lobes is found to be uniform except in S. engleri var. engieri. Each corolla lobe is beset with either one or two foveae. Foveae are naked or either partly or wholly fimbriated along their margins. No vascular tissue was observed entering the foveae. The taxonomic importance of the the floral character states is discussed.     

A flower with several secretions: anatomy,secretion composition,and functional aspects of the floral secretory structures of Chelonanthus viridiflorus (Helieae—Gentianaceae)

Floral secretory structures have been reported for Gentianaceae; however, morphoanatomical studies of these glands are rare. We described the development and secretory activity of the colleters and nectaries throughout the floral development of Chelonanthus viridiflorus. We collected flower buds, flowers at anthesis, and fruits to be investigated using light and scanning electron microscopy. We performed histochemical tests on the secretion of colleters and used glycophyte to confirm the presence of glucose in nectar. Colleters are located on the ventral surface of sepals and nectaries occur in four regions: (i) the dorsal and (ii) ventral surfaces of sepals; (iii) apex of petals; and (iv) base of ovary. The colleters have a short peduncle and a secretory portion with homogeneous cells. They are active in flower buds and secrete polysaccharides and proteins. In flowers at anthesis, they begin to senescence presenting protoplast retraction, cell collapse, and lignification; these characteristics are intensified in fruit. The nectaries of sepals and petals have two to five cells surrounding a central cell through which the secretion is released. Nectaries are numerous, forming a nectariferous area on the dorsal surface of sepals, like that observed on petals, and can form isolated units on the ventral surface of sepals. They are active from flower buds to fruits. A region with secretory activity was identified at the base of the ovary. The secretion of colleters acts in the protection of developing organs, while nectaries are related to defenses against herbivores and the supply of nectar to potential robbers or pollinators.

     

Dendroid colleters on vegetative and reproductive apices in Alibertia sessilis (Rubiaceae) differ in ultrastructure and secretion

In this work we compare the structure and secretion of dendroid colleters on stipules, bracts and sepals of Alibertia sessilis, a non-nodulate Rubiaceae species from Brazilian cerrado, with notes on the plant phenology. Samples were processed according to usual methods for anatomy, histochemistry and ultrastructure. Colleters are conical and constituted by a central axis of elongated parenchyma cells from which radiate numerous epidermal cells. Epidermal cells are cylindrical on the vegetative apex and digitiform or bulbous on reproductive apex. Both colleters produce hydrophilic and lipophilic compounds. On the vegetative apex, epidermal cells present numerous well-developed Golgi bodies associated with a network of smooth endoplasmatic reticulum (SER), scarce oil bodies and profiles of rough endoplasmatic reticulum (RER), indicating the involvement of these glands in the production of mainly polysaccharides in addition to protein and lipids. Differently, epidermal cells on bracts and sepals present abundant and prominent oil drops, fewer Golgi bodies and a well developed network of SER with locally dilated cisterns indicating predominance of lipids. Ecrine and granulocrine mechanisms are common to colleters of both apices. We hypothesize that exudates protect vegetative meristems and developing organs against desiccation in the dry season and against insects and pathogens during the wet season. Predominantly lipidic secretion protects the floral organs against dehydration in the dry season and can attract floral visitants. These aspects are relevant if one considers that A. sessilis inhabits the cerrado, an environment characterized by a well-delimited dry season, high irradiance and elevated vapor pressure deficits.     

Calycine colleters of seven species of Apocynaceae (Apocynoideae) from Brazil

The structure and organization of calycine colleters belonging to four genera of Apocynaceae are described. Calycine colleters were found in all species. All colleters had the same histological composition, but morphological differences were observed in four species. Most colleters were of the standard type, and possible deviations resulted in three morphological types: bifurcated, laminar, and sessile. Mechanisms of cell separation, proliferation, and elongation may explain the origin of the new types. As a consequence of morphological changes, the secretory surface was expanded in the bifurcated, laminar, and sessile glands. Most colleters were in a post-secretory phase, but a hydrophilic secretion was observed in Mandevilla pycnantha and Mesechites mansoana . A larger secretory surface, together with the extension of the secretory phase in adult flowers, were major shifts in the calycine colleters of Apocynaceae, and are possibly correlated with the functional and ecological aspects of these organs. Three patterns of distribution of calycine colleters were observed: alternate, opposite, or indefinitely distributed. The alternate pattern was not homogeneous, and three subtypes were recognized: four-, five-, and ten-grouped colleters. The number of calycine colleters was variable between taxa and even within the same species.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 152 , 387–398.     

Anatomical structure and secretion compounds of colleters in nine Ilex species (Aquifoliaceae) from southern South America

In order to clarify whether the structures observed at the base of the petiole of the genus Ilex are colleters resulting from stipules, the anatomy, vascularization and secretions of these supposed glandular structures were analysed in nine species. This is the first report of colleters in Ilex. Stipular colleters replace the stipules in all species studied and are characterized by the presence of vascular traces. In addition to the stipular colleters, three other types of colleter were distinguished: standard and lachrymiform colleters found on the leaf teeth or crenations, and sessile colleters found on the margins of the floral bracts. Their basic structure consists of a central core of parenchymatous cells surrounded by one layer of palisade secretory epidermal cells. Histochemical tests were also performed on secretions; proteins were found in the secretions studied, but glucose was not. The glandular origin of the stipular colleters is confirmed on the basis of their position, secretions and anatomy. Analyses of the colleter‐secreted proteins distinguished two different groups of Ilex species. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 160 , 197–210.     

The Development, Structure and Function of Dendroid Colleters in Psychotria kirkii Hiern (Rubiaceae)

The dendroid colleters of the leaf nodulated Rubiaceous shrubPsychotria kirkii Hiern. have been studied with respect to theirdevelopment, structure and function. The colleters, which arisefrom the adaxial surface of stipules of apical and lateral shoots,secrete a protein/carbohydrate mucilaginous substance in whichis maintained a colony of leaf nodule bacteria. The colletersare multicellular and multiseriate, consisting of a two to fourcell thick stalk from which radiate up to 70 elongate secretorybranch cells. Cuticle envelops both stalk and branch cells inearly developmental stages and as secretory activity increasesthis cuticle is largely lost in two different ways. The majorpart is forced off the branch cell surface through the passageof a largely carbohydrate component of the mucilage which surroundsthe colleters: a second method of cuticle loss involves thepassage from the cell of small electron-translucent bodies whichbecome coated with cuticle as they exit the cell. The mucilagein which the bacterial cells are found provides a vehicle wherebythe bacteria are able to enter the leaves, thus leading to theinitiation of leaf nodules. Psychotria kirkii Hiern., secretory dendroid colleters, symbiosis, ultrastructure, trichome development     

Colleters in Bathysa cuspidata (Rubiaceae): Development,ultrastructure and chemical composition of the secretion

This paper describes the development of colleters of Bathysa cuspidata, Rubiaceae, considering anatomical, histochemical and ultrastructural aspects and going from first differentiation stages until senescence. Further, the chemical composition of the secretion is investigated. The samples were prepared according to the usual techniques for light microscopy and scanning and transmission electron microscopy. Electrophoresis and thin layer chromatography (TLC) were used to confirm the results obtained in the histochemical tests. The colleters occur at the ventral surface of the stipules which protect the leaf primordia as well as the shoot meristem. The origin of the colleters is mixed, involving protoderm and ground meristem. The Bathysa colleters are of the standard type or are bifurcated; this latter type is documented here for the first time for Rubiaceae. Colleter secretion is a mucilage rich in protein, as determined by histochemical tests and confirmed by chemical analysis. Phenolic compounds and terpenes were detected only in the colleters themselves, but not in the secretion. The epithelial cells present conspicuous nuclei and nucleoli and the cytoplasm is rich in dictyosomes, endoplasmic reticulum, mitochondria, vesicles and small vacuoles with a fibrillar content. The accumulation of phenolic compounds and terpenes, the formation of a large central vacuole, the increase of the intercellular and subcuticular spaces occupied by the secretion and, finally, the darkening and the wilting of the colleters characterize the senescence of these structures. The secretion process of the colleters of B. cuspidata suggests a process of programmed cell death.     

Colleters in Turnera and Piriqueta (Turneraceae)

The anatomy of colleters was examined by light and scanning electron microscopy in 25 species of Turnera and nine species of Piriqueta. Based on morphology, four categories of colleters were recognized: standard, sessile, lachrymiform and trochleariform, all of which differ in shape and length/width ratio. They all have a similar anatomy: they consist of an axis of parenchymatous cells, sheathed by a palisade epidermis. The standard type is the most widespread in the studied taxa; the lachrymiform example was found in those species of Piriqueta with setiform glandular hairs; only one trochleariform example appeared in T: diffusa. The sessile type is considered to be a morphological transitional form between extrafloral nectaries and colleters. This is the first record of sessile, lachrymiform and trochleariform colleters. The anatomy of colleters is compared with other secretory structures such as glandular trichomes and extrafloral nectaries.     

Trichome forms in Ardisia (Myrsinaceae) in relation to the bacterial leaf nodule symbiosis

Symbiotic leaf-nodule bacteria in nodulated members of Rubiaceae live in mucilage secreted by colleters located on stipules within buds. These differ from colleters on most nodule-free species. This study was undertaken to examine buds of Ardisia and the related monotypic Amblyanthus of Myrsinaceae to see if nodulated species had secretory structures dissimilar from those of nodule-free species. Buds removed from herbarium specimens (61 species) and live plants (3 species) were paraffin-sectioned. Diverse trichome forms occur, including dimorphism between adaxial and abaxial trichomes in some species. Species within each subgenus were arranged according to trichome form: peltate scale, irregularly capitate, capitate, sessile capitate, bicellular capitate, and uniseriate. Only seven Ardisia species (all in subgenus Crispardisia, widely assumed to have bacteria in marginal leaf nodules of all 30 species) have short-lived trichomes bearing one or more elongate, swollen, distal cells that appear to be secretory cells. These trichomes are analogous to the dendroid or brushlike colleters of nodulated Rubiaceae. Druses occur in most subgenera and this appears to be by far the most predominant crystal type m Ardisia.     

Development, Structure and Cytochemistry of Resin-secreting Colleters of Gardenia gummifera (Rubiaceae)

The structure, ontogeny and cytochemistry of stipular colletersof Gardenia gummifera are described. The repeated division ofa few adaxial protodermal and subprotodermal cells of the youngstipule and the subsequent elongation by the latter resultsin the formation of a standard-type colleter. A developed colleterhas outer palisade-like glandular cells covered by a continuouscuticle and inner layers of elongated columnar cells. Enzymelevels in the palisade-like epidermal cells in the colletersindicate their active role in secretion. The secretion is resinous,occurs in the young colleters, and accumulates between the cellsand the cuticle. The cuticle later ruptures and releases thesecretory product, which drenches the young shoot apex. Gardenia gummifera L, stipule, colleters, resin, ontogeny, cytochemistry     

Secretory hairs in Gentiana and allied genera (Gentianaceae, subtribe Gentianinae) from the Iberian Peninsula

Eleven species from six different sections of the genus Gentiana , as well as one species each of genera Gentianella (G. campestris), Gentianopsis (G. ciliata), Comastoma (C. tenellum) and Swertia (S. perennis) have been studied by light microscopy for the presence of hairs in floral as well as in vegetative parts. Hairs are produced in the calyx and vegetative leaves of all of them, and also in the corollae of the last three species. They fall into two different types: those found in the corolla of Gentianopsis ciliata are non-secretory, while in the rest of the species studied, and also in the calyx and leaves of G. ciliata , they produce a mucilaginous secretion. Calycine and foliar hairs are always produced in the adaxial epidermis at the base of the foliar organ, and are considered as mucilage secreting colleters. The presence of colleters in vegetative organs has not been adequately considered in previous taxonomic accounts, in spite of their presumed significance.