Leaf secretory structures in Rosa lucieae (Rosaceae): two times of secretion-two ecological functions?

Secretory trichomes and colleters are two of the secretory structures whose exudates may cover the body of the plant. Such secretions comprise resins or mucilages which are associated with an array of ecological roles. In Rosaceae, secretory trichomes have been reported for the leaves while colleters associated with leaf teeth. Our study aimed to identify the secretory structures of Rosa lucieae and understand the ecological role played by these glands as interpreted by morphoanatomical and histochemical studies. Samples from developing and fully mature leaves were collected, fixed, and processed according to usual techniques for light and scanning electron microscopy. In R. lucieae, colleters are restricted to the leaf and stipular margins and are associated with the teeth. They present a parenchymatous axis surrounded by a secretory palisade epidermis and usually fall off after the secretory activity is finished. Different from colleters, secretory trichomes are persistent. They present a multicellular secretory head and stalk. They are found at the base of the leaflet, petiolule, rachis, and petiole and occasionally on the stipular and leaf margins. The colleters predominantly secrete mucilages while the secretory trichomes secrete lipids and terpenes, both via cuticle rupture. The secretory activity of colleters is predominant in the leaf primordia, holding leaflets together and protecting meristems and leaves from desiccation, while the secretory trichomes maintain their secretory activity at different stages of leaf development, protecting different regions of the leaf against pathogens and herbivores.

Nutritive tissue rich in reserves in the cell wall and protoplast: the case of Manihot esculenta (Euphorbiaceae) galls induced by Iatrophobia brasiliensis (Diptera, Cecidomyiidae).

The galls can offer shelter, protection, and an adequate diet for the gall-inducing organisms. Herein, we evaluated the structure of Manihot esculenta leaves and galls induced by Iatrophobia brasiliensis in order to identify metabolic and cell wall composition changes. We expected to find a complex gall with high primary metabolism in a typical nutritive tissue. Non-galled leaves and galls were subjected to anatomical, histochemical, and immunocytochemical analyses to evaluate the structural features, primary and secondary metabolites, and glycoproteins, pectins, and hemicelluloses in the cell wall. The gall is cylindric, with a uniseriate epidermis, a larval chamber, and a parenchymatic cortex divided into outer and inner compartments. The outer compartment has large cells with intercellular spaces and stocks starch and is designated as storage tissue. Reducing sugars, proteins, phenolic compounds, and alkaloids were detected in the protoplast of inner tissue cells of galls, named nutritive tissue, which presents five layers of compact small cells. Cell walls with esterified homogalacturonans (HGs) occurred in some cells of the galls indicating the continuous biosynthesis of HGs. For both non-galled leaves and galls, galactans and xyloglucans were broadly labeled on the cell walls, indicating a cell growth capacity and cell wall stiffness, respectively. The cell wall of the nutritive tissue had wide labeling for glycoproteins, HGs, heteroxylans, and xyloglucans, which can be used as source for the diet of the galling insect. Manihot esculenta galls have compartments specialized in the protection and feeding of the galling insect, structured by nutritive tissue rich in resource compounds, in the cell walls and protoplast.

Unraveling the secretion mechanism of the curious nectaries in Gentianaceae.

Unusual nectaries were anatomically described as being usual traits for Gentianaceae. They are small, avascularized, and formed by 3 to 5 rosette cells with labyrinthine walls around one central cell. Such as nectaries have been reported for stems, petals, and sepals of different species of the family, however, there is no information on the mechanisms involved with the synthesis and release of secretion. Thus, this work aimed to unravel the mechanism of secretion and exudation of nectar for these curious nectaries using Calolisianthus speciosus as a model. Samples were processed according to standard methods for light and electron microscopy. Leaf and sepal nectaries were described, as were those of the apex of petals where ants were observed patrolling a darkened region. The enzymatic method was used for the detection of sugars, proteins, and amino acids in leaf and sepal exudates. The nectaries of petals of C. speciosus are similar to those of its leaves, sepals, and stem, although their activities are asynchronous. Polysaccharides were detected on the labyrinthine walls of rosette cells and protein in the opposite region of the cytoplasm. Labyrinthine walls increase the contact surface between rosette cells and the central cell, allowing for the transfer of secretion. After accumulation, the secretion is released to the subcuticular space of the central cell through disruption of the cuticle. The secretion and exudation of nectar were elucidated and involve distinct organelles.

The short but useful life of Prepusa montana Mart. (Gentianaceae Juss.) leaf colleters-anatomical, micromorphological, and ultrastructural aspects.

Colleters are secretory structures involved in the protection of young and developing plant organs. Although the presence of colleters in Gentianales is described as a synapomorphy, studies on the morphofunctionality of colleters and the mechanisms underlying the synthesis and release of colleter secretion in Gentianaceae are scarce. Here, we described the ontogeny and the morphological and functional aspects of colleters of Prepusa montana, revealed the nature of the key compounds present in the secretion, and explored the cellular aspects of the synthesis and release of secretion and senescence of colleters. Samples of the stem apical meristem with leaf primordium and young leaves; adult and senescent leaves were observed using light and electron microscopy. The colleters, located in the axil of the leaf, have a protodermal origin and develop asynchronously. They are digitiform, possessing a short peduncle and a secretory head containing homogeneous cells with dense cytoplasm and abundant endoplasmic reticulum and Golgi bodies. The secretion, composed of polysaccharides and proteins, is accumulated in schizogenous spaces and released through the separation of peripheral secretory cells and loosening of the external periclinal wall. Presumably, senescence is caused by programmed cell death. The morphoanatomical characterization of P. montana leaf colleters described here is the first record for the genus and the peculiar accumulation of colleter secretion in schizogenous spaces expanding our knowledge on the diversity of these secretory structures. Our results also provide insights into programmed cell death as an eminent topic related to secretory structures.

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.

Calycinal secretory structures in Calolisianthus pedunculatus (Cham. & Schltdl) Gilg (Gentianaceae): anatomy, histochemistry, and functional aspects.

Secretory structures were little studied in Gentianaceae. Glandular areas on the calyx dorsal region are commonly reported for Helieae species, the main tribe of Gentianaceae. So, the elucidation of nature of glandular areas is particularly relevant. Trichomes secreting mucilage, interpreted as colleters, are reported only for the sepals of Gentianinae species. We aimed to anatomically characterize and identify the nature of the calycinal secretory structures in Calolisianthus pedunculatus. Samples from floral buds, flowers, and fruits were collected, fixed, and processed following usual procedures for light and scanning electron microscopies. Histochemical tests were performed to determine the nature of the secretion. Glucose, fructose, and sucrose were measured with an ELISA reader. Colleters occur on the sepal ventral region and are composed of a multicellular secretory head and a stalk. These structures secrete polysaccharides and proteins, and the secretion is probably released through cuticle microchannels. Nectaries, on the other hand, occur on the sepal dorsal region. They are formed by 3-5 cells arranged in rosettes circling a central cell or pore. These structures also secrete polysaccharides (mainly fructose), lipids, and proteins. The identification of the secretory structures in the sepals of Calolisianthus pedunculatus highlights the importance of anatomical studies in this family. The interpretation of the glandular areas on the calyx of the Helieae species as nectaries has been proven, as well as the confirmation of colleters as common structures in the sepals of Gentianaceae. Besides the taxonomic and phylogenetic importance of nectars and colleters, we highlight the importance of the secretion for the protection of floral buds against dehydration.

Morphoanatomical and physiological changes in Bauhinia variegata L. as indicators of herbicide diuron action.

The wide use of the herbicide diuron has compromised surrounding uncultivated areas, resulting in acute and/or chronic damage to non-target plants. Thus, the aim of this research was to evaluate physiological and morphoanatomical responses in Bauhinia variegata L. plants to different doses of diuron. Seedlings of 90-day-old B. variegata were transplanted into 10liter pots. After an acclimation period (about 30 days), treatments consisting of different diuron doses were applied: 0 (control), 400, 800, 1600, and 2400g ai ha-1. The experiment was conducted in a randomized block design in a 5×5 factorial scheme with five doses of diuron five evaluation times, and five replicates per treatment. Anatomical and physiological injuries were observed in leaves of Bauhina variegata 10h after diuron application. Disruption of waxes was observed on both sides of the leaves of plants exposed since the lowest dose. Plasmolysis in cells were observed in treated leaves; more severe damage was observed in plants exposed to higher doses, resulting in rupture of epidermis. The diuron herbicide also caused gradual reduction in the gas exchange and chlorophyll fluorescence variables. Among the morphoanatomical and physiological variables analyzed, the non-invasive ones (e.g., ETR, YII, and Fv/Fm) may be used as biomarkers of diuron action in association with visible symptoms. In addition, changes in leaf blade waxes and chlorophyll parenchyma damage may also be considered additional leaf biomarkers of diuron herbicide action.

Extrafloral nectaries in neotropical Gentianaceae: occurrence, distribution patterns, and anatomical characterization.

PREMISE OF THE STUDY: Extrafloral nectaries (EFNs) are structures that secrete nectar and protect plants against herbivores and pathogens. In Gentianaceae, these structures have been described in species of Calolisianthus, Fagraea, and Anthocleista and are important morphological markers for taxonomic and phylogenetic studies. To establish a foundation for further studies, we investigated the occurrence, distribution patterns, and anatomy of EFNs on leaves of 27 species belonging to 13 genera and three tribes of neotropical Gentianaceae. • METHODS: Leaf samples were diaphanized, stained with basic fuchsin, and mounted in glycerinated gelatin. Cross sections were obtained from material embedded in methacrylate or paraffin, stained, and mounted in Permount. Polysaccharides were histochemically stained with periodic acid-Schiff stain. Samples were also examined with scanning electron microscopy. • KEY RESULTS: Unusual EFNs, visible only with light microscopy, were formed of modified epidermal cells. Each EFN consisted of 2-5 secretory cells encircling a central cell. The EFNs varied in size and in the shape and arrangement of the adjacent cells surrounding the secretory cells. EFNs occurred in all analyzed species as isolated units distributed throughout the leaf blade or as aggregates; aggregates were generally visible to the naked eye. Based on their occurrence as aggregates or isolated units and on their location on the leaf blade, six distribution patterns were identified. • CONCLUSIONS: This is the first comprehensive study of EFNs on the leaves of neotropical Gentianaceae. The data suggested that NEFs evolved from isolated units for NEFs in aggregates. The results represent a new source of data for future ecological, systematic, and phylogenetic studies in Gentianaceae.