Anastomosing laticifer in the primary and secondary structures of Calotropis procera (Aiton) W.T.Aiton (Apocynaceae) stems.

An in-depth understanding of the development and distribution of laticifer (latex secretory structure) will be important for the production of both rubber and medicines and will support studies on plant adaptations to their environments. We characterize here and describe the ontogenesis of the laticifer sytem in Calotropis procera (Apocynaceae), an invasive subshrub species in arid landscapes. Anatomical and histochemical evaluations of the primary and secondary structures of the stem were carried out on a monthly basis during a full year, with ultrastructural evaluations of laticifer on the stem apex during the rainy season. In the primary structure, laticifer differentiate early from procambium and ground meristem cells of the cortex and medulla and become concentrated adjacent to the external and internal phloem of the bicollateral bundles. In the secondary structure, laticifer differentiates from fusiform derivative cells of the phloem close to the sieve-tube elements. The laticifer is of the articulated, anastomosing, branched type, and it originates from precursor cells that loose the transversal and longitudinal walls by dissolution. Latex is a mixture of terpenes, alkaloids, flavonoids, mucilage, and proteins. The apical meristem and vascular cambium where the laticifer system begins its development are active throughout the year, including during the dry season. The vascular cambium produces phloem with laticifer precursor cells during the rainy season, with high temperatures and long days. The ability of C. procera to grow under water deficit conditions and produce laticifer throughout the year contribute to its wide distribution in arid environments.

Laticifer ontogenesis and the chemical constituents of Marsdenia zehntneri (Apocynaceae) latex in a semiarid environment.

MAIN CONCLUSION: Anastomosed laticifers with intrusive growth produce latex containing methyl comate and betulin with economic and ecological value in arid environments. Climatic factors influence laticifer development in the apical meristem and vascular cambium. Latex is a complex emulsion with high medicinal as well as ecological value related to plant survival. Marsdenia zehntneri is a shrubby plant that grows on limestone outcrops in the semiarid regions of Brazil. We sought to characterize the ontogenesis of the laticifers of this species and to relate that process to climatic seasonality and phenology through anatomical, ultrastructural, and micro-morphometric evaluations of the apical meristem and vascular cambium. The histochemistry of the secretory structure was investigated and the chemical composition of the latex was analyzed. Phenological assessments were performed by monitoring phenological events for 1 year. The laticifers network of M. zehntneri permeates the entire primary and secondary body of the plant, providing a wide distribution system of defensive compounds. Its laticifers, of a distinct mixed type (anastomosed, with intrusive growth), are numerous and voluminous in the apical meristem but scarce and minute in the secondary phloem. Latex secretion involves the participation of oleoplasts, polysomes, and dictyosomes. Methyl 2,3-dihydroxy-ursan-23-oate, methyl 3-hydroxy-ursan-23-oate, and betulin are encountered in high proportions in the latex and have ecological and medicinal functions. The development of primary laticifers is related to the resumption of apical meristem activity with increasing day length at the end of the austral winter. The development of secondary laticifers is related to high summer temperatures and rainfall that favor vascular cambium activity. The wide distribution of laticifers, their seasonal pattern of secretion, and their latex composition contribute to the adaptation of M. zehntneri to its natural environment.

Pericarp histogenesis and histochemistry during fruit development in Butia capitata (Arecaceae).

Palm fruits show great structural complexity, and in-depth studies of their development are still scarce. This work aimed to define the developmental stages of the fruit of the neotropical palm Butia capitata and to characterize the ontogenesis of its pericarp. Biometric, anatomical, and histochemical evaluations were performed on pistillate flowers and developing fruits. The whole fruit develops in three phases: (I) histogenesis (up to 42 days after anthesis - DAA), when the topographic regions of the pericarp are defined; (II) pyrene maturation (42 to 70 DAA), when the sclerified zone of the pericarp is established; and (III) mesocarp maturation (70 to 84 DAA), when reserve deposition is completed. During pericarp ontogenesis (i) the outer epidermis and the outer mesophyll of the ovary give origin to the exocarp (secretory epidermis, collenchyma, parenchyma, sclerenchyma, and vascular bundles); (ii) the median ovarian mesophyll develops into the mesocarp, with two distinct topographical regions; (iii) the inner ovarian epidermis originates the endocarp; and in the micropylar region, it differentiates into the germination pore plate, a structure that protects the embryo and controls germination. (iv) Most of the inner region of the mesocarp fuses with the endocarp and, both lignified, give rise to the stony pyrene; (v) in the other regions of the mesocarp, carbohydrates and lipids are accumulated in a parenchyma permeated with fiber and vascular bundles. The development of the B. capitata pericarp presents high complexity and a pattern not yet reported for Arecaceae, which supports the adoption of the Butia-type pyrenarium fruit class.

Ontogenesis of Resin Ducts and Secretory Process in Protium spruceanum (Burseraceae) Stems.

The objective of this work was to characterize the ontogenesis of Protium spruceanum secretory ducts, to evaluate the effects of seasonality on that process, and to characterize the chemical nature of the resin. Morphometric, anatomical, micromorphometric, histochemical, and ultrastructural evaluations of shoot apexes and chemical analyses of the resin were performed. The ducts of schizolysigenous origin are distributed in the primary and secondary phloem. The subsecretory tissue is meristematic and can restore the secretory epithelium. Secretory epithelial cells have wall thickening resembling that of the Casparian strip that regulates secretion reflux. The main resin compounds are pentacyclic triterpenoids, α- and ß-amyrins, and α- and ß-amyrenones, which are reported here for the first time for this species. The presence of electron-dense and electron-opaque structures, in the secretory epithelial cells, are compatible with the triterpenes and mucilage identified in the resin. Rising temperatures, rainfall, and increasing day length induce the formation of ducts in the vascular cambium throughout Spring/Summer. The abundant production of resin rich in pentacyclic triterpenes indicates the potential use of the species for medicinal and cosmetic purposes. The understanding that secretory processes are concentrated during the Spring/Summer seasons will contribute to the definition of resin extraction management strategies.

Chemical profile and antioxidant activity in Diplopterys pubipetala (Malpighiaceae).

This work aimed to carry out phytochemical prospecting and evaluate the antioxidant potential of Diplopterys pubipetala, a species of Malpighiaceae family that has not yet been studied.In qualitative analyses of hydroethanolic extracts of leaves and stems were detected the presence of flavonoids, alkaloidsand terpenes. The histochemical evaluation evidenced a greater distribution of these compounds in the tissues of leaf when compared with those of stem. The analysis by mass spectrometry allowed the identification of prenylated xanthones and glycoside flavonoids that have not yet been reported in the literature. The antioxidant activity of the stem extract was considered moderate (IAA = 0.79), but the leaves presented a strong antioxidant activity (IAA = 1.6). In this work we present information about the phytochemicals of D. pubipetala, showing that the species is promising in obtaining compounds with medicinal potential mainly antioxidant potential.

Reserve mobilization dynamics and degradation pattern of mannan-rich cell walls in the recalcitrant seed of Mauritia flexuosa (Arecaceae).

Most seeds store reserves, which mobilization after germination is complex and diversified among plant species. Information on the reserve mobilization in recalcitrant seeds (i.e., intolerant to desiccation) is scarce. The aim of this work was to characterize the dynamics of reserve mobilization and the degradation pattern of the endospermic cell walls in the recalcitrant seeds of the neotropical palm Mauritia flexuosa. Biometric, anatomical, histochemical, ultrastructural and immunocytochemistry assessments were performed in the endosperm and haustorium (structure of the seedling involved in reserve mobilization), during germination and throughout seedling development. Endo-ß-mannanase activity was assessed. The main reserves stored in the seeds are mucilage in the living protoplast and, mainly, heteromannans in the thick cell walls of the endosperm cells. The reserve mobilization extends for about 180 days, in four phases. During germination, the embryonic reserves are catabolized, which induces the mobilization of the endosperm by establishing the flow of water and carrying substances to the haustorium. After germination, the cells of the endosperm actively control the process of their degradation, which results in the formation of the digestion zone. The growth of the haustorium promotes the crushing of endospermic cells and facilitates the entry of substances via the apoplastic route. The pattern of degradation of endospermic cells involves three phases: 1) mobilization of the vacuolar content by symplastic route; 2) increased vacuole turgor pressure, directing the content of the cytoplasm to the cell walls; 3) degradation of cell walls.

Mucilaginous Secretions in the Xylem and Leaf Apoplast of the Swamp Palm Mauritia flexuosa L.f. (Arecaceae).

Mauritia flexuosa palms inhabit wetland environments in the dry, seasonal Brazilian savanna (Cerrado) and produce mucilaginous secretions in the stem and petiole that have a medicinal value. The present study sought to characterize the chemical natures of those secretions and to describe the anatomical structures involved in their synthesis. Chemical analyzes of the secretions, anatomical, histochemical analyses, and electron microscopy studies were performed on the roots, stipes, petioles, and leaf blades. Stipe and petiole secretions are similar, and rich in cell wall polysaccharides and pectic compounds such as rhamnose, arabinose, xylose, mannose, galactose, and glucose, which are hydrophilic largely due to their hydroxyl and carboxylate groups. Mucilaginous secretions accumulate in the lumens of vessel elements and sclerenchyma fibers of the root, stipe, petiole, and foliar veins; their synthesis involves cell wall loosening and the activities of dictyosomes. The outer faces of the cell walls of the parenchyma tissue in the mesophyll expand to form pockets that rupture and release pectocellulose substances into the intercellular spaces. The presence of mucilage in the xylem, extending from the roots to the leaf veins and continuous with the leaf apoplast, and sub-stomatal chambers suggest a strategy for plant water economy.

Secondary-cell-wall release: a particular pattern of secretion in the mucilaginous seed coat of Magonia pubescens.

PREMISE: Plant mucilages are composed of strongly hydrophilic polysaccharides and contribute to seed germination and seedling establishment. The myxospermic seeds of Magonia pubescens, a Cerrado (neotropical savanna) tree species, produces a voluminous mucilage capsule when hydrated. The development of the mucilaginous layer, the process of mucilage secretion and its role in seed germination was not previously studied so far. METHODS: Morphological, anatomical, histochemical, and ultrastructural evaluations of the seed coat during seed development were undertaken. The formation of the mucilage capsule was followed using scanning electron microscopy, and the coat's effects on seed hydration and germination were evaluated after experimental manipulation of the seed coat. RESULTS: The mucilaginous layer is contained in the outer coat of the seed. The mucilage-secreting cells accumulate proteins in the outer periclinal region and acidic polysaccharides in the inner periclinal region of the periplasmic space. Neutral polysaccharides, which form the loosely organized secondary wall, form a folding, basket-like structure surrounding the acidic polysaccharides. The protoplast collapses at maturity. With hydration, the mucilage expands, breaks the epidermal layer, and forms a mucilage capsule around the seed. The mucilaginous seed coat does not increase the germination rate. CONCLUSIONS: Upon mucilage hydration, the secondary cell walls forming the network of neutral polysaccharides are released, along with proteins, and help retain the acidic polysaccharides-forming a peculiar architecture that imparts integrity and consistency to the mucilage capsule. As winged seeds are not usually buried, the mucilage capsule favors seedling hydration, contributing to its establishment on the soil surface.

Atemoya fruit development and cytological aspects of GA3-induced growth and parthenocarpy.

The exogenous application of GA3 to atemoya tree flowers induces parthenocarpy, and in association with artificial pollination, it increases the fruit size. Morphological, anatomical, ultrastructural, and chemical aspects were evaluated during development of (1) fruit produced by artificial pollination (AP), (2) fruit from AP followed by the application of 250 ppm GA3, and (3) parthenocarpic fruit induced by the application of 1000 ppm GA3. Fruit growth showed a sigmoidal pattern, with development occurring in three phases: (I) cell division, (II) cell differentiation, and (III) maturation. Phase I presented cells with large nuclear volumes and a large population of organelles, phase II presented cells with a reduction in cytoplasm and an increase in vacuole volume, and phase III presented cells with an increase in plastids with reserve compounds. The application of GA3, in association with pollination, precedes cytological events and delays when applied exclusively. GA3 promotes the growth of pollinated fruits by stimulating cell division and expansion, which occur in association with reduced seed production, and the GA3 induces parthenocarpy by maintaining division and stimulating cell expansion. The absence of seeds accounts for the smaller size of the parthenocarpic fruits, and the lower accumulation of calcium accounts for less firm fruit.

Cytological and histochemical evaluations reveal roles of the cotyledonary petiole in the germination and seedling development of Mauritia flexuosa (Arecaceae).

The cotyledonary petiole (CP) completely envelops the embryo axis during embryogenesis in Arecaceae. There is little information available, however, on the roles of that structure in seed germination and initial seedling development-crucial plant life cycle phases. The study therefore sought to evaluate the roles of CP in the germination and post-seminal development of the recalcitrant seeds of Mauritia flexuosa, an ecologically and economically important neotropical palm. The CP and the embryo/vegetative axis were evaluated during germination and initial seedling development using standard morphological, anatomical, histochemical, and ultrastructural methodologies. Evaluations of dormant seeds incubated for 60 days were also performed. The CP (a) promotes seedling protrusion in the germination, extending the embryo axis outside the seed; (b) protects the vegetative axis through the development of coating rich in phenolic compounds and lignin; (c) participates in reserve translocation, with the conversion of its own proteinaceous/mucilaginous reserves into transitional starch, as well as acting in the transport of endospermic reserves; (d) favors aeration, with the formation of pathways among stomata, substomatal chambers, and intercellular spaces; (e) controls seedling morphogenesis by modulating the curvature of the vegetative axis; and (f) contributes to overcoming seed bank dormancy through cytological alterations (protein synthesis and mitochondrial proliferation). The cotyledonary petiole of palms is a unique and multifunctional structure among angiosperms, with crucial roles in germination and seedling establishment.

Ontogeny of anastomosed laticifers in the stem apex of Hancornia speciosa (Apocynaceae): a topographic approach.

Latex is a complex plant secretion with both ecological and economic importance. There is little information currently available on the cytological aspects of the ontogenesis of anastomosed laticifers, the ducts originating through the lysis of adjacent cell walls. Hancornia speciosa is a tree typical of the Cerrado (neotropical savanna) biome. Its latex has medicinal value and is also used to produce rubber. The ontogenesis of its laticifers and the process of latex synthesis are described here. Structural, cytochemical, and ultrastructural analyses of the stem apex and phytochemical analyses of the latex were performed. Laticifer ontogenesis begins early in promeristem cells and subsequently extends through the procambial region. The laticifer precursor cells demonstrate intense metabolic activity, evidenced by starch accumulation and the proliferation of mitochondria, dictyosomes, endoplasmic reticulum, and ribosomes-resulting in the thickening of the cell walls and accumulations of oil droplets in the cytoplasm and fibrous materials in the vacuoles. The ontogenetic process culminates with the partial dissolution of adjacent cell walls and the collapse of the cytoplasm, giving rise to anastomosed laticifers distributed throughout the phloem and adjacent regions of the cortex and medulla. The latex itself is composed of terpenes, mucilage, proteins, alkaloids, and organelle residues that form an emulsion. Laticifer development takes place in three phases: (1) the formation of the emulsion in the promeristem, (2) anastomosis and the collapse of the cytoplasm in the distal region of the procambium, and (3) the maturation of laticifers and latex storage in a central vacuole in the proximal region of the procambium.

Ontogenesis and functions of saxophone stem in Acrocomia aculeata (Arecaceae).

BACKGROUND AND AIMS: The underground saxophone stem systems produced by seedlings of certain palm species show peculiar growth patterns and distinctive morphologies, although little information is available concerning their development and function. We studied the ontogenesis of the saxophone stem in Acrocomia aculeata, an important neotropical oleaginous palm, and sought to experimentally define its function. METHODS: Morpho-anatomical evaluations were performed during 240 d on seedlings using traditional methodologies. The tuberous region of the structure was submitted to histochemical tests and evaluated by transmission electron microscopy. The aerial portions of 130 1- to 3-year-old greenhouse plants were removed and their continuous growth capacity was evaluated after 30 d. Severed saxophone stems were also stored at room temperature (average 25 °C) for up to 90 d and then cultured for 60 d to evaluate root and shoot emission. KEY RESULTS: The development of the saxophone stem is distinct from other underground systems previously described, and involves three processes: growth and curvature of the cotyledonary petiole, expansion and curvature of the hypocotyl, and expansion of the plumule internodes. The tuberous region stores water and starch, as well as lesser amounts of mucilage and oil. Growth of the aerial portion occurred in 84 % of the separated saxophone stems and in 53 % of the stems held in storage. CONCLUSIONS: The saxophone stem represents an important adaptation of A. aculeata to anthropogenically impacted and/or dry environments by promoting the burial of both the shoot meristem and storage reserves, which allows the continuous growth of aerial organs.

Anatomy, Histochemistry, and Antifungal Activity of Anacardium humile (Anacardiaceae) Leaf.

Leaves of Anacardium humile are used in Brazilian traditional medicine for the treatment of intestinal disturbances and skin lesions. This study aimed to define leaf diagnostic structural characters, to propose a new method of phytochemical analysis of secretions, prospect flavonoids and alkaloids, and to evaluate their inhibitory activity on Candida albicans. Common anatomical, phytochemical, and microbiological methods were used. Leaves of Anacardium occidentale were used as a reference for the structural analyses. The main structural characters were closed vascular system, absence of ducts at the medulla, bilateral mesophyll, absence of bundle sheath extension, and secretory idioblasts at the xylem. The ducts present schizogenous origin, and secreting activity is restricted to the initial phases of leaf blade expansion. The proposed new phytochemical method is practical and inexpensive and has potential for wide application. The abundance of tannins and flavonoids is related to medicinal use. A single peak in high-performance liquid chromatography indicated the presence of a pure substance not previously reported. The extract had a strong inhibitory effect on C. albicans. The obtained results confirm the potential of A. humile for the prospection of new bioactive compounds.

Structure, histochemistry and phytochemical profile of the bark of the sobol and aerial stem of Tontelea micrantha (Celastraceae - Hippocrateoideae).

The bark of the underground stem of Tontelea micrantha (Mart. ex. Schult.) A. C. Sm., a native Brazilian Cerrado species, is used in folk medicine for treating kidney ailments. The structures of the underground and the aerial stems were examined and their barks were analyzed for the presence of secondary metabolites. Bark fragments were processed according to conventional techniques in plant anatomy and their chemical compositions examined using histochemical and phytochemical tests, thin layer chromatography, and high-efficiency liquid chromatography. The underground stem is a sobol with unusual cambial activity. Laticifers that secrete terpenoids were present in the cortex and phloem of both organs and can contribute to the identification of the species in field. Druses were present in both barks, but mono-crystals were only observed in the sobol. Tannins, flavonoids, alkaloids, and terpenoids occurred in both types of bark, but carotenoids were only detected in the sobol. The similarities between these two organs indicate that the aerial stem bark has potential medicinal use and represents a plausible alternative to harvesting the sobol, which could contribute to the preservation of natural populations of this species.

Stenospermy and seed development in the "Brazilian seedless" variety of sugar apple (Annona squamosa).

Stenospermy was identified in naturally occurring sugar-apple (Annona squamosa) mutants with great potential for use in genetic improvement programs. However, to date, there have been no detailed studies of the development of aspermic fruit in this species. The aim of the present study was to characterize the anatomy of developing fruit in the 'Brazilian Seedless' mutant. Flower buds in pre-anthesis and developing fruits were subjected to common plant anatomy techniques. The abnormal ovules are unitegmic and orthotropic and have a long funiculus. There is evidence of fertilization, including the presence of embryos in early development and the proliferation of starch grains in the embryo sac. However, the embryos and embryo sac degenerate, although this does not affect pericarp development. Ovule abortion does not occur. The perisperm, which is formed from the peripheral layers of the nucellus, fills the cavity left by the embryo sac. The mature fruit contains numerous small sterile seeds with abundant perisperm and unlignified integument that is restricted to the micropylar region. The majority of perisperm cells are living and appear to be metabolically active in the periphery. Therefore, stenospermy leads to the formation of sterile seeds in A. squamosa, and the perisperm possibly play an important role in fruit development.

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.