Alexandra Antunes Mastroberti

Identification and expression analysis of castor bean (Ricinus communis) genes encoding enzymes from the triacylglycerol biosynthesis pathway

Castor bean (Ricinus communis) oil contains ricinoleic acid-rich triacylglycerols (TAGs). As a result of its physical and chemical properties, castor oil and its derivatives are used for numerous bio-based products. In this study, we survey the Castor Bean Genome Database to report the identification of TAG biosynthesis genes. A set of 26 genes encoding six distinct classes of enzymes involved in TAGs biosynthesis were identified. In silico characterization and sequence analysis allowed the identification of plastidic isoforms of glycerol-3-phosphate acyltransferase and lysophosphatidate acyltransferase enzyme families, involved in the prokaryotic lipid biosynthesis pathway, that form a cluster apart from the cytoplasmic isoforms, involved in the eukaryotic pathway. In addition, two distinct membrane bound diacylglycerol acyltransferase enzymes were identified. Quantitative expression pattern analyses demonstrated variations in gene expressions during castor seed development. A tendency of maximum expression level at the middle of seed development was observed. Our results represent snapshots of global transcriptional activities of genes encompassing six enzyme families involved in castor bean TAG biosynthesis that are present during seed development. These genes represent potential targets for biotechnological approaches to produce nutritionally and industrially desirable oils.

Development of mucilage cells of Araucaria angustifolia (Araucariaceae)

Summary.The roles of mucilage cells were investigated through morphological and cytological analysis during leaf development in young Araucaria angustifolia plants. Differentiation began in leaf primordia in the shoot apex, when the young cells underwent a greater increase in volume in comparison with other mesophyll cells. The mucilage polysaccharides were synthesized by dictyosomes, from where they were taken by large vesicles and released into a cavity formed by detachment of the tonoplast, which was separated from the cytoplasm. At the end of differentiation, the cell was completely filled with mucilage, a gel consisting of a denser reticular structure surrounding less dense regions. The nucleus and cytoplasm were degenerated in mature cells. The A. angustifolia mucilage cells presented some cytological resemblances to the mucilage cells of members of some dicotyledonous families; however, differences in the dictyosomes and the secretion route were observed. Translocation and water storage of solutes was suggested by the use of the hydroxy pyrenetrisulfonic acid tri-sodium salt apoplastic tracer. The tonoplast detachment, dechromatinization, nuclear condensation, and general degeneration of the membrane systems observed during maturity indicated a programmed cell death process, one not yet described for angiosperm mucilage cells.

Heterogeneity of silica and glycan-epitope distribution in epidermal idioblast cell walls in Adiantum raddianum laminae

Laminae of Adiantum raddianum Presl., a fern belonging to the family Pteridaceae, are characterised by the presence of epidermal fibre-like cells under the vascular bundles. These cells were thought to contain silica bodies, but their thickened walls leave no space for intracellular silica suggesting it may actually be deposited within their walls. Using advanced electron microscopy in conjunction with energy dispersive X-ray microanalysis we showed the presence of silica in the cell walls of the fibre-like idioblasts. However, it was specifically localised to the outer layers of the periclinal wall facing the leaf surface, with the thick secondary wall being devoid of silica. Immunocytochemical experiments were performed to ascertain the respective localisation of silica deposition and glycan polymers. Epitopes characteristic for pectic homogalacturonan and the hemicelluloses xyloglucan and mannan were detected in most epidermal walls, including the silica-rich cell wall layers. The monoclonal antibody, LM6, raised against pectic arabinan, labelled the silica-rich primary wall of the epidermal fibre-like cells and the guard cell walls, which were also shown to contain silica. We hypothesise that the silicified outer wall layers of the epidermal fibre-like cells support the lamina during cell expansion prior to secondary wall formation. This implies that silicification does not impede cell elongation. Although our results suggest that pectic arabinan may be implicated in silica deposition, further detailed analyses are needed to confirm this. The combinatorial approach presented here, which allows correlative screening and in situ localisation of silicon and cell wall polysaccharide distribution, shows great potential for future studies.

Asymmetric cytokinesis guide the development of pseudomonads in Rhynchospora pubera (Cyperaceae)

The late stages of microsporogenesis in the family Cyperaceae are marked by the formation of an asymmetrical tetrad, degeneration of three of the four nuclei resulting from meiosis and the formation of pseudomonads. In order to understand the cytological changes involved in the development of pseudomonads, a combination of 11 different techniques (conventional staining, cytochemistry procedures, immunofluorescence, FISH and transmission electron microscopy: TEM) were used to study the later stages of microsporogenesis in Rhynchospora pubera. The results demonstrated the occurrence of two cytoplasmic domains in the pseudomonads, one functional and the other degenerative, which are physically and asymmetrically separated by cell plate with an endomembrane system rich in polysaccharides. Other changes associated with endomembrane behaviour were observed, such as a large number of lipid droplets, vacuoles containing electron‐dense material and concentric layers of endoplasmic reticulum. Concomitant with the isolation of degenerative nuclei, the tapetal cells also showed evidence of degeneration, indicating that both tissues under programmed cell death (PCD), as indicated by immunofluorescence and TEM procedures. The results are significant because they associate cellular polarisation and asymmetry with different cytoplasmic domains, and hence open new possibilities for studying cellular compartmentalisation and PCD.

Leaf anatomy of Araucaria angustifolia (Bertol.) Kuntze (Araucariaceae)

Leaf anatomy of Araucaria angustifolia (Bertol.) Kuntze (Araucariaceae)). Immature and mature leaves of juvenile and adult plants of Araucaria angustifolia (Araucariaceae) were observed with the objective of updating the morphoanatomical data of the leaves of this species, which were restricted to basic descriptions in previous studies. The observations, made in optical allowed to establish anatomical differences among mature leaves of juvenile and adult plants in relation to the number of palisade parenchimal layers, the number of compartmented cells and the transfusion tissue development. Epidermis, the albuminous cells, the phloem, and the transfusion tissue descriptions are in disagreement with the data obtained data by different authors. The epidermal tissue and the hypodermis differ entirely when the plant is still juvenile, being inferred that these tissues would soon perform the protection function against mechanical damages and water loss, the vital characteristics during the first development months of young offspring. RESUMO - (Anatomia foliar de Araucaria angustifolia (Bertol.) Kuntze (Araucariaceae)). Foram observadas folhas imaturas e maduras de plantas jovens e adultas de Araucaria angustifolia (Araucariaceae), com o objetivo de atualizar os dados morfoanatomicos das folhas desta especie, cujos estudos anteriores se restringiam a descricoes basicas. As observacoes efetuadas em microscopia optica permitiram estabelecer diferencas anatomicas entre folhas maduras de plantas jovens e adultas, com relacao ao numero de camadas do parenquima palicadico, numero de celulas compartimentadas e desenvolvimento do tecido de transfusao. As descricoes para a epiderme, celulas albuminosas, floema e tecido de transfusao, nao estao de acordo com os dados obtidos por diferentes autores. O tecido epidermico e hipoderme se diferenciam por completo quando a planta ainda e jovem, inferindo-se que estes tecidos desempenhariam logo a funcao de protecao contra danos mecânicos e perda de agua, caracteristas vitais durante os primeiros meses de estabelecimento da planta jovem.

Immunocytochemistry of the mucilage cells of Araucaria angustifolia (Bertol.) Kuntze (Araucariaceae)

The use of monoclonal antibodies for specific pectic epitopes is an important tool in the study of the cell wall. Throughout the development of mucilage cells of Araucaria angustifolia (Bertol.) Kuntze, a gradient of distribution was observed in relation to the pectic de-esterification, as well as to the increase of galactan and arabinan epitope distribution, and to the reduction of arabinogalactans proteins (AGPs) epitope at maturity. AGP and methyl-esterified homogalacturonan (HGA) were present in the mucilage. Galactans and arabinans were also observed in the mucilage, though with weak labelling. Degradation of AGP in the maturity of mucilage cells, in cell wall, as well as in the secretion, could be involved in the programmed cell death (PCD). Different labellings found among parenchyma and mucilage cells suggested differences in the cell wall properties of the mucilage cells.

Capsule structure in three species of Dyckia (Bromeliaceae): Ontogenetic and taxonomic issues1

Abstract Dyckia is characterized by conserved external floral and fruit morphology. Considering the conservative morphology of Dyckia fruits, anatomical features could be an important source of phylogenetically useful characters. The objectives of this study were to characterize fruit ontogeny and dehiscence in three species of Dyckia (Dyckia distachya, Dyckia reitzii, and Dyckia remotiflora), and in the process to identify characters that contribute to the systematics of the genus and family. Differences were found among species in the number of mesophyll/mesocarp layers, presence of pluristratified hypodermis, presence of mucilage secretory structures, and presence of perivascular bundle sheath extensions. In addition, a xerochastic mechanism of dehiscence in Dyckia denticidal capsules is described here for the first time. As a potential source of characters, fruit anatomical features can be useful at the generic and specific levels.

Cytological differentiation and cell wall involvement in the growth mechanisms of articulated laticifers in Tabernaemontana catharinensis A.DC. (Apocynaceae)

The cellular mechanisms of laticifer growth are of particular interest in plant biology but are commonly neglected. Using transmission electron microscopy and immunocytochemical methods, we recorded cytological differentiation and evaluated the cell wall involvement in the growth of articulated laticifers with intrusive growth in the mature embryo and plant shoot apex of Tabernaemontana catharinensis. The incorporation of adjacent meristematic cells into the laticifer system occurred in the embryo and plant shoot apex, and the incorporated cells acquired features of laticifer, confirming the laticifers’ action-inducing mechanism. In the embryo, this was the main growth mechanism, and began with enlargement of the plasmodesmata and the formation of pores between laticifers and meristematic cells. In the plant shoot apex, it began with loose and disassembled walls and the reorientation of the cortical microtubules of the incorporated cell. Plasmodesmata were absent in these laticifers. There was stronger evidence of intrusive growth in undifferentiated portions of the plant shoot apex than in the embryo. The numerous plasmodesmata in laticifers of the embryo may have been related to the lower frequency of intrusive growth. Intrusive growth was associated with presence of arabinan (increasing wall flexibility and fluidity), and absence of galactan (avoiding wall stiffness), and callose (as a consequence of reduction in symplastic connections) in the laticifer walls. The abundance of low de-methyl-esterified homogalacturonan in the middle lamella and corners may reestablish cell-cell bonding in the laticifers. The cell wall features differed between embryo and plant shoot apex and are directly associated to laticifer growth mechanisms.

Anatomical analyses of floral and extrafloral secreting structures indicate the presence of nectaries and colleters in Stanhopea grandiflora Lindl.

Anatomical studies involving secreting structures in Stanhopeinae have described lipid-producing structures, the osmophores, these structures have been linked to pollinator attraction. Stanhopea, which belongs to the subtribe Stanhopeinae, has Neotropical distribution and is exclusively pollinated by male Euglossini bees, which are attracted to the aromatic compounds exuded by osmophores—a secreting structure that produces volatile lipids. However, due to the structural diversity found in this genus and the lack of data on which foragers visit these flowers, our aim is to elucidate floral anatomical aspects of the Stanhopeinae group, focusing on the secreting structures of Stanhopea grandiflora Lindl., an orchid that occurs in the Amazon region. Analyses were performed under bright-field microscopy and scanning electron microscopy. Osmophores, nectaries, idioblasts and glandular trichomes were the secreting structures observed in Stanhopea grandiflora. The osmophores are responsible for attracting and offering rewards the male Euglossini bees, which are their exclusive pollinators, while the nectaries offering nectar to the foragers Dolichoderus and Azteca ants which in turn offer protection against herbivores. Nectariferous stomata and glandular trichomes role similar to those of colleters are described in the first record of the subtribe Stanhopeinae.

Development of the Epidermal Cells of the Pinnules of Adiantum raddianum C.Presl (Pteridaceae): Environmental Adaptive Plastidial Characteristics

Abstract Plants have different strategies for adapting to environmental conditions, such as characteristics that allow them to be more efficient in shady or sunny environments. Those that grow in dimly lit environments often have a photosynthetic epidermis. However, Adiantum raddianum, known as the maidenhair fern, is a species found in sunny environments that has this characteristic. Within the abaxial and adaxial epidermal cells of the leaf pinnules of this species, there are arm-like projections where chloroplasts agglomerate. The goal of this study was to describe the development of the epidermal cells of A. raddianum, describe the morphological characteristics of the chloroplasts in these cells, and interpret any cytological characteristics that this species might have as a result of an adaptive survival strategy. The study found that the arm-like projections within the epidermis develop when the leaves are young and still exhibit circinate vernation. Cytological observations revealed a plastidial dimorphism, where there was variation in the arrangement of the thylakoid system, and the presence of stromules, which may help establish a connection among chloroplasts and between these organelles and mitochondria and peroxisomes. Descriptions of the stromules and plastidial dimorphism, made in this study, can be included with other known epidermal adaptive strategies (e.g., plastidial movement and mucilage secretion), which help this plant to survive under different environmental conditions.