Ovary peltate trichomes of Zeyheria montana (Bignoniaceae): developmental ultrastructure and secretion in relation to function

Histochemical Analysis and Ultrastructure of Trichomes and Laticifers of Croton gratissimus Burch. var. gratissimus (Euphorbiaceae)

Croton gratissimus (Lavender croton) possesses three distinct secretory structures. These include lepidote and glandular trichomes and non-articulated unbranched laticifers. The lepidote trichomes form a dense indumentum on the abaxial surface of the leaves and canopy the glandular trichomes. Although assumed to be non-glandular, transmission electron microscopy (TEM) indicated high metabolic activity within the stalk and radial cells. Glandular trichomes are embedded in the epidermal layer and consist of a single cell which forms a prominent stalk and dilated head. Laticifers occur on the mid-vein of leaves and are predominantly associated with vascular tissue. In the stems, laticifers are associated with the phloem and pith. Both trichome types and laticifers stained positive for alkaloids, phenolic compounds, and lipids. Positive staining for these compounds in lepidote trichomes suggests their involvement in the production and accumulation of secondary metabolites. These metabolites could provide chemical defense for the plant and potentially be useful for traditional medicine.

Peltate trichomes in the dormant shoot apex of Metrodorea nigra, a Rutaceae species with rhythmic growth

In Metrodorea nigra, a Rutaceae species with rhythmic growth, the shoot apex in the dormant stage is enclosed by modified stipules. The young organs are fully covered with peltate secretory trichomes, and these structures remain immersed in a hyaline exudate within a hood-shaped structure. Our study focused on the morpho-functional characterization of the peltate trichomes and cytological events associated with secretion. Shoot apices were collected during both dormant and active stages and processed for anatomical, cytochemical and ultrastructural studies. Trichomes initiate secretion early on, remain active throughout leaf development, but collapse as the leaves expand; at which time secretory cavities start differentiation in the mesophyll and secretion increases as the leaf reaches full expansion. The subcellular apparatus of the trichome head cells is consistent with hydrophilic and lipophilic secretion. Secretion involves two vesicle types: the smaller vesicles are PATAg-positive (periodic acid/thiocarbohydrazide/silver proteinate) for carbohydrates and the larger ones are PATAg-negative. In the first phase of secretory activity, the vesicles containing polysaccharides discharge their contents through exocytosis with the secretion accumulating beneath the cuticle, which detaches from the cell wall. Later, a massive discharge of lipophilic substances (lipids and terpenes/phenols) results in their accumulation between the wall and cuticle. Release of the secretions occurs throughout the cuticular microchannels. Continued protection of the leaves throughout shoot development is ensured by replacement of the collapsed secretory trichomes by oil-secreting cavities. Our findings provide new perspectives for understanding secretion regulation in shoot apices of woody species with rhythmic growth.

Glandular trichomes of the flowers and leaves in Millingtonia hortensis (Bignoniaceae)

Three types of the glandular trichomes are developed on the flowers and leaves of Millingtonia hortensis. Morphology, cell ultrastructure and content of the volatile compounds are specific to each trichome type. The aim of this study was to characterize the structural and histochemical features of the glandular trichomes (GTs) of two types localized on the different flower parts and leaves in Millingtonia hortensis, as well as to identify the composition of the internal pool of metabolites. The peltate GTs are most common; they are founded on peduncle, calyx, ovary, and leaves. GTs consist of 12-24-cell disk-shaped head and a single-celled neck. The capitate GTs are located on corolla tube and have four to eight-cell head, single-celled neck and a wide multicellular stalk. A series of histochemical reactions and fluorescent microscopy revealed the various substances in the chemical composition of GTs. Acid polysaccharides are predominately identified in the capitate trichomes of the corolla tube and peltate trichomes of calyx, terpenes present in larger quantity in the trichomes of the corolla tube and ovary, whilst phenolic substances prevail in the trichomes of the calyx and ovary. GTs of each type are characterized by specific ultrastructural traits. Smooth endoplasmic reticulum (SER) and leucoplasts prevail in the peltate trichomes of peduncle, calyx and ovary; Golgi apparatus is the common organelle in the capitate trichomes of the corolla tube and peltate trichomes of calyx; the huge aggregates of the RER cisterns there are in cytoplasm of all leaf trichomes. Synthesized secretion accumulates in the subcuticular cavity of all GTs except the leaf peltate trichomes. In the trichomes of the leaves secretion is stored in the thick upper cell wall with the wide cutinized layer. For the first time content of the internal pool of metabolites from the flowers and leaves was identified by GC-MS. Seventeen compounds, including alcohols, fatty acid derivatives, monoterpenes, sesquiterpenes, and benzenoids were identified. 1-octen 3-ol, 3-carene, methyl salicylate, p-hydroxybenzeneethanol and 1-hydroxy-2,4-di-tertbutyl-benzene were the main compounds of the flower scent. We consider GTs of the reproductive organs in M. hortensis synthesizing acid polysaccharides and volatile compounds as secretory structures attracting of pollinators, whereas the leaf peltate trichomes accumulating predominately non-volatile phenols, protect young vegetative shoots against small herbivorous insects and pathogens.

Glandular trichomes of Robinia viscosa Vent. var. hartwigii (Koehne) Ashe (Faboideae, Fabaceae)-morphology, histochemistry and ultrastructure

MAIN CONCLUSION

Permanent glandular trichomes of Robinia viscosa var. hartwigii produce viscous secretion containing several secondary metabolites, as lipids, mucilage, flavonoids, proteins and alkaloids. Robinia viscosa var. hartwigii (Hartweg's locust) is an ornamental tree with high apicultural value. It can be planted in urban greenery and in degraded areas. The shoots, leaves, and inflorescences of this plant are equipped with numerous persistent glandular trichomes producing sticky secretion. The distribution, origin, development, morphology, anatomy, and ultrastructure of glandular trichomes of Hartweg's locust flowers as well as the localisation and composition of their secretory products were investigated for the first time. To this end, light, scanning, and transmission electron microscopy combined with histochemical and fluorescence techniques were used. The massive glandular trichomes differing in the distribution, length, and stage of development were built of a multicellular and multiseriate stalk and a multicellular head. The secretory cells in the stalk and head had large nuclei with nucleoli, numerous chloroplasts with thylakoids and starch grains, mitochondria, endoplasmic reticulum profiles, Golgi apparatus, vesicles, and multivesicular bodies. Many vacuoles contained phenolic compounds dissolved or forming various condensed deposits. The secretion components were transported through symplast elements, and the granulocrine and eccrine modes of nectar secretion were observed. The secretion was accumulated in the subcuticular space at the trichome apex and released through a pore in the cuticle. Histochemical and fluorescence assays showed that the trichomes and secretion contained lipophilic and polyphenol compounds, polysaccharides, proteins, and alkaloids. We suggest that these metabolites may serve an important function in protection of plants against biotic stress conditions and may also be a source of phytopharmaceuticals in the future.

Taxonomic traits in the microstructure of flowers of parasitic Orobanche picridis with particular emphasis on secretory structures

Orobanche picridis is an obligate root parasite devoid of chlorophyll in aboveground organs, which infects various Picris species. Given the high level of phenotypic variability of the species, the considerable limitation of the number of taxonomically relevant traits (mainly in terms of generative elements), and the low morphological variation between species, Orobanche is regarded as one of the taxonomically most problematic genera. This study aimed to analyse the taxonomic traits of O. picridis flowers with the use of stereoscopic and bright-field microscopy as well as fluorescence, scanning, and transmission electron microscopy. The micromorphology of sepals, petals, stamens, and pistils was described. For the first time, the anatomy of parasitic Orobanche nectaries and the ultrastructure of nectaries and glandular trichomes were presented. Special attention was paid to the distribution and types of glandular and non-glandular trichomes as well as the types of metabolites contained in these structures. It was demonstrated that the nectary gland was located at the base of the gynoecium and nectar was secreted through modified nectarostomata. The secretory parenchyma cells contained nuclei, large amyloplasts with starch granules, mitochondria, and high content of endoplasmic reticulum profiles. Nectar was transported via symplastic and apoplastic routes. The results of histochemical assays and fluorescence tests revealed the presence of four groups of metabolites, i.e. polyphenols (tannins, flavonoids), lipids (acidic and neutral lipids, essential oil, sesquiterpenes, steroids), polysaccharides (acidic and neutral polysaccharides), and alkaloids, in the trichomes located on perianth elements and stamens.

Glandular trichomes of the leaves in three Doronicum species (Senecioneae, Asteraceae): morphology, histochemistry, and ultrastructure

Two types of glandular tichomes (GTs) develop on the leaves in three Doronicum species. The purpose of the work was to establish common and distinctive morphological, anatomical, histochemical, and ultrustructural features of the trichomes. It turned out that differences between types of trichomes are more significant than interspecific ones. For each Doronicum species, differences between GTs of two types include the dimensions, intensity of coloration by histochemical dyes, as well as ultrastructural features of the cells. The GTs of the first type are higher than GTs of the second type. Two to three upper cell layers of the first trichomes develop histochemical staining, whereas in the second ones, only apical cells give a positive histochemical reaction. In all trichomes, polysaccharides, polyphenols, and terpenoids are detected. In the GTs of the first type, polysaccharides are synthesized in larger quantity; in the GTs of the second type, synthesis of the secondary metabolites predominates. Main ultrastructural features of the GTs of the first type include proliferation of RER and an activity of Golgi apparatus denoting the synthesis of enzymes and pectin; however, development of SER, diversiform leucoplasts with reticular sheaths, and chloroplasts with peripheral plastid reticulum also demonstrate the synthesis of lipid substances. The ultrastructural characteristics of the second type GTs indicate the primary synthesis of lipid components. Secretion is localized in a periplasmic space of the upper cell layers. The secretory products pass through the cell wall, accumulate in the subcuticular cavity, and rupture it.

Ultrastructure and secretion of glandular trichomes in species of subtribe Cajaninae Benth (Leguminosae, Phaseoleae)

The subtribe Cajaninae of papilionoid legumes has a pantropical distribution and comprises approximately 490 species. These species have diversified throughout dry environments where there are high temperatures and strong light. The subtribe stands out because all its representatives have vesicular glands. In addition, bulbous-based and capitate trichomes are important secretory structures present in all genera of the Cajaninae. We analyzed the ultrastructure and histochemistry of these glandular trichome types in leaflets of the three species of the subtribe. Using transmission electron microscopy and histochemical analyses, we link the glandular secretions to subcellular structures. We here report for the first time the type of exudate and ultrastructure of the glands of subtribe Cajaninae. Terpenoids and phenolics were confirmed by histochemistry tests, and we observed that the organelles responsible for biosynthesis of oils are the most representative in these glands. Each glandular trichome showed particular ultrastructural features compatible with the compounds produced. We suggest that these glandular trichomes, with their respective exudates, act in defense against herbivory and against possible damage by ultraviolet radiation.

Secretory Structures of Pogostemon auricularius: Morphology, Development, and Histochemistry

Pogostemon auricularius, an aromatic plant in Lamiaceae, has wide application in pharmaceutical preparations. However, little is known about the secretory structures that contain the medicinal compounds. In this study, two kinds of glandular trichome types, including peltate glandular trichomes and short-stalked capitate trichomes, were identified in the leaves and stems by cryo-scanning electron microscope. Oil secretion from the glands contained lipids, flavones, and terpenes, and the progresses of secretion were different in the two glands types. The investigation by transmission electron microscope indicated that the endoplasmic reticulum system and plastids were involved in the biosynthesis of oils in the two glandular trichomes. The vacuoles showed a new role in the oil preparations and storage. The synthesized oil could be transported from the head cell to the sub-cuticular space by different way in the two glands. Comparative analysis of the development, distribution, histochemistry and ultrastructures of the secretory structures in Pogostemon auricularius led us to propose that the two glands may make different contribution to the collection of medicinal compounds. Furthermore, the characteristics of two glands in the secretory stage probably indicated the synthesizing site of metabolite.

Nectar Replaced by Volatile Secretion: A Potential New Role for Nectarless Flowers in a Bee-Pollinated Plant Species

The presence of nectarless flowers in nectariferous plants is a widespread phenomenon in angiosperms. However, the frequency and distribution of nectarless flowers in natural populations, and the transition from nectariferous to nectarless flowers are poorly known. Variation in nectar production may affect mutualism stability, since energetic resource availability influences pollinators' foraging behavior. Here, we described the spatial and temporal nectar production patterns of Jacaranda oxyphylla, a bee-pollinated species that naturally presents nectarless flowers. Additionally, we compared nectariferous and nectarless floral disks in order to identify histological, subcellular and chemical changes that accompanied the loss of nectar production ability. For that we used standard methods for light and transmission electron microscopy, and gas chromatography coupled to mass spectrometry for chemical analyses. We verified that 47% of flowers did not produce nectar during the whole flower lifespan (nectarless flowers). We also observed remarkable inter-plant variation, with individuals having only nectarless flowers, others only nectariferous ones and most of them showing different proportions of both flower types, with variable nectar volumes (3-21 μl). Additionally, among nectariferous flowers, we registered two distinct rhythms of nectar production. 'Early' flowers produced nectar from 0 to 24 h, and 'late' flowers produced nectar from 24 to 48 h of anthesis. Although disks from nectariferous and nectarless flowers displayed similar histological organization, they differed strongly at subcellular level. Nectariferous ('early' and 'late') flowers exhibited a cellular apparatus typical of nectar secretion, while nectarless flowers exhibited osmophoric features. We found three aliphatic and one aromatic compound(s) that were detected in both the headspace of flowers and the disks of nectarless flowers, but not the disks of nectariferous flowers Although the remarkable variation in nectar availability may discourage pollinator visits, nectarless flowers might compensate it by producing volatile compounds that can be part of floral scent, acting as chemical attractants. Thus, nectarless flowers may be helping to maintain pollination in this scenario of trophic resource supply scarcity. We suggest that J. oxyphylla can be transitioning from a nectar-based pollination system to another resource-based or even to a deceit mechanism of pollination.

Floral features of two species of Bulbophyllum section Lepidorhiza Schltr.: B. levanae Ames and B. nymphopolitanum Kraenzl. (Bulbophyllinae Schltr., Orchidaceae)

Two representatives of section Lepidorhiza, previously sometimes considered conspecific, Bulbophyllum levanae and Bulbophyllum nymphopolitanum, demonstrated both similarities and differences in floral features. There were significant differences in the length of sepals and micromorphological features of the labellum. In both species, osmophores are located on the extended apices of sepals and possibly on petals. An abundance of proteins in tepals is probably associated with the unpleasant scent of the flowers, whereas the thin wax layers on the epidermis are probably involved in the maintenance of the brilliance of floral tepals, which strongly attracts flies. In all tepals of both species, we noted the presence of dihydroxyphenolic globules in the cytoplasm after staining with FeCl₃. Comparison with ultrastructure results revealed that they were associated with plastids containing plastoglobuli. The most remarkable feature was the presence of a prominent periplasmic space in the epidermal cells of both investigated species. Furthermore, in the labellum of B. levanae, the cuticle contained microchannels. The combination of periplasmic space and microchannels has not previously been recorded.

Structure and functioning of oil cavities in the shoot apex of Metrodorea nigra A. St.-Hil. (Rutaceae)

This study investigates the histology and subcellular features of secretory cavities during the development of the shoot apex of Metrodorea nigra A. St.-Hil. in order to better understand the functioning of these glands. This Rutaceae species is a very suitable model for studying secretory cavity life span, since the shoot apex exhibits both dormant and growth stages during its annual cycle. Shoot apices were collected during the dormant and growth stages from populations of M. nigra growing under natural conditions. Materials were processed using standard techniques for light and electron microscopy. The secretory cavities originate under the protodermis, and their initiation is restricted to the early developmental stage of shoot organs, which are protected by a hood-shaped structure. Secretory cavities have a multi-seriate epithelium surrounding a lumen that expands schizolysigenously. Oil production begins before lumen formation. When the shoot apex resumes development after the dormant stage, the glands remain active in oil secretion in the developing shoot apex and fully expanded leaves. The mature epithelial cells are flattened and exhibit very thin walls, large oil bodies, leucoplasts surrounded by endoplasmic reticulum, and mitochondria with unusual morphology. The tangential walls of the epithelial cells facing the lumen undergo continuous peeling. The vacuole extrusion appears to be the primary mode of release oil into the lumen, in an exocytotic way. The continuity of oil secretion is ensured by the replacement of the damaged inner epithelial cells by divisions in the parenchyma layer that surround the oil gland, likely a meristematic sheath.

Ultrastructural changes in the epidermis of petals of the sweet orange infected by Colletotrichum acutatum

Postbloom fruit drop (PFD) is an important disease caused by the fungus Colletotrichum acutatum. PFD is characterised by the formation of necrotic lesions on the petals and stigmas of flowers as well as premature abscission of the fruit in Citrus spp. We compare the ultrastructure of the epidermis of uninoculated Citrus sinensis petals with that of petals inoculated with the fungus to understand the changes that occur upon C. acutatum infection. Healthy petals have a cuticle with parallel striations covering the uniseriate epidermis. This pattern consists of vacuolated parietal cells whose cytoplasm contains mitochondria, plastids with an undeveloped endomembrane system and a slightly dense stroma, a poorly developed rough endoplasmic reticulum, polysomes, few lipid droplets, and a nucleus positioned near the inner periclinal wall. In damaged regions, the cytoplasm of some cells is densely packed with well-developed endoplasmic reticulum, a large number of hyperactive dictyosomes, numerous mitochondria, and many lipid droplets. The plastids have an electron-dense stroma, starch grains, and a large amount of electron-dense lipid droplets, which can be released into vacuoles or the endoplasmic reticulum. Multivesicular bodies and myelin bodies are frequently observed in the vacuole, cytoplasm, and periplasmic space. Vesicles migrate through the cell wall and are involved in the deposition of cuticular material. In the later stages of infection, there is deposition of new cuticle layers in plaques. The outer periclinal walls can be thick. These observations indicate that epidermal cells respond to the pathogen, resulting in cuticular and parietal changes, which may limit further infection.

Zeyheria montana Mart. (Bignoniaceae) as source of antioxidant and immunomodulatory compounds with beneficial effects on intestinal inflammation

OBJECTIVES

Zeyheria montana is a medicinal plant used in Brazilian folk medicine for treating skin affections, ulcers, inflammation and diarrhoea, and as an antisyphilitic and antiblenorrhagic agent, but little is known about its mechanisms of action. Herein, a bio-guided assay was carried out to further evaluate its antioxidant and immunomodulatory effects, and the possible benefits on experimental intestinal inflammation.

METHODS

Extracts, partitions, fractions and isolated compounds were tested for inhibition of lipid peroxidation. Isolated compounds were tested in vitro for its antioxidant and immunomodulatory action prior to in-vivo evaluation in trinitrobenzenesulfonic acid-induced rat colitis.

KEY FINDINGS

Two major compounds were identified in the leaf dichloromethane extract: 3'-hydroxy-5,7,4'-trimethoxyflavone and 6-hydroxy-5,7-dimethoxyflavone, which exhibited an antioxidant activity. The compounds protected the colonic glutathione levels in more than 90% despite the absence of protection against the gross macroscopic colonic damage. In addition, the compounds inhibited IL-1ß secretion by macrophages in 91.5% and 72.7% respectively, whereas both reduced IL-6 secretion in about 44.5%.

CONCLUSIONS

The major active compounds from Z. montana leaves exerted antioxidant and immunomodulatory effects, endorsing the use of Z. montana in folk medicine as an anti-inflammatory agent. However, further investigation is still needed regarding medicinal plants and the identification of candidate compounds for the treatment of the inflammatory bowel diseases.

Trichomes related to an unusual method of water retention and protection of the stem apex in an arid zone perennial species

It is well known that trichomes protect plant organs, and several studies have investigated their role in the adaptation of plants to harsh environments. Recent studies have shown that the production of hydrophilic substances by glandular trichomes and the deposition of this secretion on young organs may facilitate water retention, thus preventing desiccation and favouring organ growth until the plant develops other protective mechanisms. Lychnophora diamantinana is a species endemic to the Brazilian 'campos rupestres' (rocky fields), a region characterized by intense solar radiation and water deficits. This study sought to investigate trichomes and the origin of the substances observed on the stem apices of L. diamantinana. Samples of stem apices, young and expanded leaves were studied using standard techniques, including light microscopy and scanning and transmission electron microscopy. Histochemical tests were used to identify the major groups of metabolites present in the trichomes and the hyaline material deposited on the apices. Non-glandular trichomes and glandular trichomes were observed. The material deposited on the stem apices was hyaline, highly hydrophilic and viscous. This hyaline material primarily consists of carbohydrates that result from the partial degradation of the cell wall of uniseriate trichomes. This degradation occurs at the same time that glandular trichomes secrete terpenoids, phenolic compounds and proteins. These results suggest that the non-glandular trichomes on the leaves of L. diamantinana help protect the young organ, particularly against desiccation, by deposition of highly hydrated substances on the apices. Furthermore, the secretion of glandular trichomes probably repels herbivore and pathogen attacks.

Ozone-induced responses in Croton floribundus Spreng. (Euphorbiaceae): metabolic cross-talk between volatile organic compounds and calcium oxalate crystal formation

Here, we proposed that volatile organic compounds (VOC), specifically methyl salicylate (MeSA), mediate the formation of calcium oxalate crystals (COC) in the defence against ozone (O3) oxidative damage. We performed experiments using Croton floribundus, a pioneer tree species that is tolerant to O3 and widely distributed in the Brazilian forest. This species constitutively produces COC. We exposed plants to a controlled fumigation experiment and assessed biochemical, physiological, and morphological parameters. O3 induced a significant increase in the concentrations of constitutive oxygenated compounds, MeSA and terpenoids as well as in COC number. Our analysis supported the hypothesis that ozone-induced VOC (mainly MeSA) regulate ROS formation in a way that promotes the opening of calcium channels and the subsequent formation of COC in a fast and stable manner to stop the consequences of the reactive oxygen species in the tissue, indeed immobilising the excess calcium (caused by acute exposition to O3) that can be dangerous to the plant. To test this hypothesis, we performed an independent experiment spraying MeSA over C. floribundus plants and observed an increase in the number of COC, indicating that this compound has a potential to directly induce their formation. Thus, the tolerance of C. floribundus to O3 oxidative stress could be a consequence of a higher capacity for the production of VOC and COC rather than the modulation of antioxidant balance. We also present some insights into constitutive morphological features that may be related to the tolerance that this species exhibits to O3.

Floral colleters in Pleurothallidinae (Epidendroideae: Orchidaceae)

PREMISE OF THE STUDY

The term colleter is applied to trichomes or emergences positioned close to developing vegetative and floral meristems that secrete a sticky, mucilaginous, and/or lipophilic exudate. Several ecological functions are attributed to these glands, but none are exclusive to colleters. Patterns of morphology and distribution of colleters may be valuable for systematics and phylogeny, especially concerning problematic and large groups such as the subtribe Pleurothallidinae, and are also essential to understand the evolution of these glands in Orchidaceae as a whole.

METHODS

We used scanning electron and light microscopy to examine the structure and occurrence of trichomes on bracts and sepals and in the invaginations of the external ovary wall (IEOW) in flowers in several developmental stages from species in seven genera.

KEY RESULTS

The exudate was composed of polysaccharides, lipophilic, and phenolic compounds. Colleters were secretory only during the development of floral organs, except for the glands in the IEOW that were also active in flowers at anthesis. After the secretory phase, fungal hyphae were found penetrating senescent trichomes.

CONCLUSIONS

Trichome-like colleters seem to be a widespread character in Epidendroideae, and digitiform colleters are possibly the common type in this subfamily. Mucilage from IEOW colleters may aid in the establishment of symbiotic fungi necessary for seed germination. The presence of colleters in the IEOW may be a case of homeoheterotopy, in which extrafloral nectaries that produce simple sugar-based secretions (as in other orchid species) have changed to glands that produce secretions with complex polysaccharides, as in Pleurothallidinae.

Development and structure of internal glands and external glandular trichomes in Pogostemon cablin

Pogostemon cablin possesses two morphologically and ontogenetically different types of glandular trichomes, one type of bristle hair on the surfaces of leaves and stems and one type of internal gland inside the leaves and stems. The internal gland originates from elementary meristem and is associated with the biosynthesis of oils present inside the leaves and stems. However, there is little information on mechanism for the oil biosynthesis and secretion inside the leaves and stems. In this study, we identified three kinds of glandular trichome types and two kinds of internal gland in the Pogostemon cablin. The oil secretions from internal glands of stems and leaves contained lipids, flavones and terpenes. Our results indicated that endoplasmic reticulum and plastids and vacuoles are likely involved in the biosynthesis of oils in the internal glands and the synthesized oils are transported from endoplasmic reticulum to the cell wall via connecting endoplasmic reticulum membranes to the plasma membrane. And the comparative analysis of the development, distribution, histochemistry and ultrastructures of the internal and external glands in Pogostemon cablin leads us to propose that the internal gland may be a novel secretory structure which is different from external glands.

Effects of the serjania erecta and zeyheria montana ethanol extracts in experimental pulpitis in rats: a histological study

OBJECTIVES

The aim of this study was to evaluate, by the semi-quantitative histological analysis, the anti-inflammatory activity of the ethanolic extracts of Serjania erecta e Zeyheria Montana, in experimental pulpits in rats.

STUDY DESIGN

In order to induce pulp inflammation, cavities were performed on the occlusal surface of the mandibular first molars of 45 male rats, without pulp exposure. The animals were distributed into 4 groups: GI, teeth without cavities; GII, single dose of saline solution via intraperitoneal (IP); GIII, single dose (IP) of 300 mg/Kg of ethanolic extract of Zeyheria montana; GIV, single dose (IP) of 300 mg/Kg of ethanolic extract of Serjania erecta. After 6, 12 and 24 hours, 5 animals of each group were killed by anesthetic overdose. The histological analyses of the pulp tissue were performed and the data analyzed by Dunn's multiple test, at significance of 5%.

RESULTS

After 12 h, the GIII presented score statistically lower (p<0.05) than positive control group. After 24 h, GIII presented inflammatory index statistically lower than the positive control (p<0.01) and Serjania erecta (p<0.05) groups.

CONCLUSION

The Zeyheria montana extract presented better anti-inflammatory activity than positive control group and Serjania erecta extract, which did not show anti-inflammatory effect in the analyzed periods.

Terpenoid biosynthesis in trichomes--current status and future opportunities

Glandular trichomes are anatomical structures specialized for the synthesis of secreted natural products. In this review we focus on the description of glands that accumulate terpenoid essential oils and oleoresins. We also provide an in-depth account of the current knowledge about the biosynthesis of terpenoids and secretion mechanisms in the highly specialized secretory cells of glandular trichomes, and highlight the implications for metabolic engineering efforts.

Functional aspects of floral nectar secretion of Ananas ananassoides, an ornithophilous bromeliad from the Brazilian savanna

BACKGROUND AND AIMS

Several members of Bromeliaceae show adaptations for hummingbird pollination in the Neotropics; however, the relationships between floral structure, nectar production, pollination and pollinators are poorly understood. The main goal of this study was to analyse the functional aspects of nectar secretion related to interaction with pollinators by evaluating floral biology, cellular and sub-cellular anatomy of the septal nectary and nectar composition of Ananas ananassoides, including an experimental approach to nectar dynamics.

METHODS

Observations on floral anthesis and visitors were conducted in a population of A. ananassoides in the Brazilian savanna. Nectary samples were processed using standard methods for light and transmission electron microscopy. The main metabolites in nectary tissue were detected via histochemistry. Sugar composition was analysed by high-performance liquid chromatography (HPLC). The accumulated nectar was determined from bagged flowers ('unvisited'), and floral response to repeated nectar removal was evaluated in an experimental design simulating multiple visits by pollinators to the same flowers ('visited') over the course of anthesis.

KEY RESULTS

The hummingbirds Hylocharis chrysura and Thalurania glaucopis were the most frequent pollinators. The interlocular septal nectary, composed of three lenticular canals, extends from the ovary base to the style base. It consists of a secretory epithelium and nectary parenchyma rich in starch grains, which are hydrolysed during nectar secretion. The median volume of nectar in recently opened 'unvisited' flowers was 27·0 µL, with a mean (sucrose-dominated) sugar concentration of 30·5 %. Anthesis lasts approx. 11 h, and nectar secretion begins before sunrise. In 'visited' flowers (experimentally emptied every hour) the nectar total production per flower was significantly higher than in the 'unvisited' flowers (control) in terms of volume (t = 4·94, P = 0·0001) and mass of sugar (t = 2·95, P = 0·007), and the concentration was significantly lower (t = 8·04, P = 0·0001).

CONCLUSIONS

The data suggest that the total production of floral nectar in A. ananassoides is linked to the pollinators' activity and that the rapid renewal of nectar is related to the nectary morphological features.

Clytostoma callistegioides (Bignoniaceae) wax extract with activity on aphid settling

A bioassay-guided fractionation of leaf extracts from Clytostoma callistegioides (Cham.) Bureau ex Griseb. (Bignoniaceae) led to isolation of a natural mixture of four fatty acids with anti-insect activity against aphids. The compounds were identified by GC-MS as palmitic, stearic, linoleic and linolenic acids and quantified as their methyl esters. The anti-aphid activity of the natural mixture was traced to linolenic and linoleic acids, as shown by the settling inhibition activity of synthetic samples. Interestingly, the saturated acids (palmitic and stearic) tested alone stimulated settling on one of the tested aphids (Myzus persicae), but not on the other tested species (Rhopalosiphum padi). Although ubiquitous, none of these free acids have been previously reported in this Bignoniaceae species. The leaf surface chemistry, which is likely involved in modulating aphid settling behavior, was further investigated for the occurrence of lipophilic substances by histochemical staining. Short, stalked glandular trichomes, previously undescribed for this species, stained with osmium tetroxide and Sudan III, suggesting that the secretion of the defensive acids is related to these surface trichomes.

Leaf glands act as nectaries in Diplopterys pubipetala (Malpighiaceae)

Leaf glands of Diplopterys pubipetala were studied with light and electron microscopy. Aspects of their secretion, visitors and phenology were also recorded. Glands occur along the margin, at the apex and at the base of the leaf blade. All the glands begin secretion when the leaf is still very young, and secretion continues during leaf expansion. The highest proportion of young leaves coincides with the beginning of flowering. The glucose-rich secretion is collected by Camponotus ants, which patrol the newly formed vegetative and reproductive branches. All the glands are sessile, partially set into the mesophyll, and present uniseriate epidermis subtended by nonvascularised parenchyma. The glands at the apex and base are larger and also consist of vascularised subjacent parenchyma. The cytoplasm of epidermal and parenchyma cells has abundant mitochondria, polymorphic plastids filled with oil droplets and a few starch grains. Golgi bodies and endoplasmic reticulum are more abundant in the epidermal cells. The parenchyma cells of the subjacent region contain chloroplasts and large vacuoles. Plasmodesmata connect all the nectary cells. The zinc iodide-osmium tetroxide (ZIO) method revealed differences in the population of organelles between epidermal cells, as well as between epidermal cells and parenchyma cells. Ultrastructural results indicate that leaf glands of D. pubipetala can be classified as mixed secretory glands. However, the secretion released by these glands is basically hydrophilic and composed primarily of sugars, hence these glands function as nectaries.

Non-volatile components of the essential oil secretory cavities of Eucalyptus leaves: discovery of two glucose monoterpene esters, cuniloside B and froggattiside A

The essential oils extracted from the embedded foliar secretory cavities of many Eucalyptus species are of economic value as pharmaceuticals and fragrance additives. Recent studies have indicated that Eucalyptus secretory cavities may not be exclusively involved in the biosynthesis and storage of essential oils. Therefore, we selected three species upon which to perform an examination of the contents of foliar secretory cavities: Eucalyptus froggattii, E. polybractea and E. globulus. This paper describes the isolation and structural characterization of two non-volatile glucose monoterpene esters, which we have named cuniloside B and froggattiside A, from within the secretory cavities of these species, and shows the presence of these compounds in solvent extracts of the leaves from two other species of Eucalyptus. Both compounds were found in high proportions relative to the essential oils extracted from the leaves. We propose that many other carbohydrate monoterpene esters previously isolated from bulk leaf extracts of various Eucalyptus species may also be localized within the non-volatile fraction of foliar secretory cavities.

Anti-inflammatory and anti-nociceptive effects of Zeyheria montana (Bignoniaceae) ethanol extract

In this work, the analgesic and anti-inflammatory activities of Zeyheria montana Mart. ethanol leaf extract were investigated at doses of 75, 150 and 300 mg/kg body weight. In the analgesic assay, against a chemical stimulus in mice, acetic acid-induced writhes were significantly inhibited by the extract at doses of 75 mg/kg (67.27%), 150 mg/kg (49.38%) and 300 mg/kg (82.87%). Also, a vigorous decrease in hyperalgesia was observed when measured after 2 h and 6 h of lipopolysaccharide stimulation of rats for all doses of extract tested. Z. montana extract, at doses of 75 and 300 mg/kg, caused very slight central analgesia in rats submitted to thermal stimulus, particularly noticeable at 30 min following treatment. The anti-inflammatory activity of Z. montana extract on carrageenan-induced oedema in rats was evaluated. The oedema development, measured at 180 min following carrageenan intraplantar injection, was significantly reduced by all tested doses: 75 mg/kg (33.30%), 150 mg/kg (45.80%) and 300 mg/kg (75.00%). The LD50 value was greater than 2000 mg/kg. These results demonstrated that the ethanol extract from Z. montana leaf possesses anti-nociceptive and anti-inflammatory activities, which could be of relevance for the pharmacological control of pain and inflammatory processes.

Pollination biology of Jacaranda oxyphylla with an emphasis on staminode function

BACKGROUND AND AIMS

Bignoniaceae is a Neotropical family with >100 genera, only two of which, Jacaranda and Digomphia, have a developed staminode. Jacaranda oxyphylla, whose flowers possess a conspicuous glandular staminode, is a zoophilous cerrado species. Here, the composition of the secretion of the glandular trichome and the influence of the staminode on the pollination biology and reproductive success of J. oxyphylla were studied.

METHODS

The floral morphology, pollen viability, stigma receptivity, nectar volume and nectar concentration were studied. Compatibility system experiments were performed and floral visitors were observed and identified. Experiments comparing the effect of staminode presence and absence on pollen removal and pollen deposition efficiency were conducted in open-pollinated flowers. Histochemistry, thin-layer chromatography (TLC) and gas chromatography coupled to flame ionization detection (GC-FID) analyses were performed to determine the main chemical components of the staminode's glandular trichome secretion.

KEY RESULTS

Flower anthesis lasted 2 d and, despite the low frequency of flower visitation, pollination seemed to be effected mainly by medium-sized Eulaema nigrita and Bombus morio bees, by the small bee Exomalopsis fulvofasciata and occasionally by hummingbirds. Small bees belonging to the genera Ceratina, Augochlora and Trigona were frequent visitors, collecting pollen. Jacaranda oxyphylla is predominantly allogamous. Staminode removal resulted in fewer pollen grains deposited on stigmas but did not affect total pollen removal. The secretion of capitate glandular trichome occurs continually; the main chemical compounds detected histochemically were phenolic and terpenoid (essential oils and resins). Monoterpene cineole, pentacyclic triterpenes and steroids were identified by TLC and GC-FID.

CONCLUSIONS

The staminode of J. oxyphyllla is multifunctional and its importance for female reproductive success was attributed mainly to the secretion produced by capitate glandular trichomes. This secretion is involved in complex chemical interactions with pollinating bees, including the solitary bees Euglossini. These bees are common pollinators of various species of Jacaranda.

Morphological patterns of extrafloral nectaries in woody plant species of the Brazilian cerrado

Extrafloral nectaries are nectar-secreting structures that are especially common among the woody flora of the Brazilian cerrado, a savanna-like vegetation. In this study, we provide morphological and anatomical descriptions of extrafloral nectaries (EFNs) occurring on vegetative and reproductive organs of several plant species from the cerrado, and discuss their function and ecological relevance. We describe the morphology and anatomy of EFNs of 40 species belonging to 15 woody families using scanning electron microscopy and light microscopy. We categorise EFNs following a structural-topographical classification, and characterise the vascularised and complex nectaries, amorphous nectaries and secretory trichomes. Fabaceae, Bignoniaceae, Malpighiaceae and Vochysiaceae were the plant families with the majority of species having EFNs. Ten species possess more than one morphotype of gland structure. Observations and experimental field studies in the cerrado support the anti-herbivore role of EFN-gathering ants in this habitat. Additional morphological studies of EFNs-bearing plants, including other growth forms (e.g. herbs and lianas), are being undertaken and will hopefully cast further light on the ecological relevance of these glands in the cerrado, especially with respect to their attractiveness to multiple visitors.