Structural and ultrastructural aspects of ontogenesis and differentiation of resin secretory cavities in Hymenaea stigonocarpa (Fabaceae‐Caesalpinioideae) leaves

Cell lysis in the formation of secretory cavities in plants has been questioned by some authors and considered as result of technical artifacts. To describe the formation of secretory resin cavities in Hymenaea stigonocarpa leaves, leaflet samples at different stages of differentiation were collected, fixed, and processed for light and electron microscopy as per usual methods. The initial cells of secretory resin cavities are protodermal and grow towards the mesophyll ground meristem; these cells then divide producing cell groups that are distinguished by the shape and arrangement of cytoplasm, and density. At the initial stages of differentiation of the secretory cavities, some central cells in these groups show dark cytoplasm and condensed nuclear chromatin. Later, there is cell wall loosening, tonoplast and plasmalemma rupture resulting in cell death. These cells, however, maintain organelle integrity until lysis, when the cell wall degrades and the plasmalemma ruptures, releasing protoplast residues, marked characteristics of programmed cell death. The secretory epithelium remains active until complete leaf expansion when the cavity is filled with resin and the secretory activity ceases. There are no wall residues between central cells in adult cavities. Our results demonstrate lysigeny and the importance of ontogenetic studies in determining the origin of secretory cavities.     

DEVELOPMENT OF BICELLULAR FOLIAR SECRETORY CAVITIES IN WHITE SNAKEROOT,EUPATORIUM RUGOSUM (ASTERACEAE)

Bicellular secretory cavities in Eupatorium rugosum occur only in foliar mesophyll, distributed uniformly from leaf tip to base, with a mean density of 450 per mm². They are absent from petiole and all other vegetative and floral organs. Each cavity contains an oily droplet, which is surrounded by two cup-shaped cells. An initial cell divides into two equal cavity cells with their shared wall always perpendicular to the epidermis. After vacuoles form, each protoplast retracts from the other and deposits a new, callosic wall around the cavity, and a thicker callose deposit on the remaining shared walls outside of the cavity. The original shared wall remains intact across the cavity until maturity. It is pulled taut by cavity cell growth and restricts further expansion except in one paradermal direction. Later, this shared wall disappears from the cavity. An oily fluid of unknown composition is secreted into the enlarging cavity. Because bicellular cavities develop neither lysigenously nor in true schizogenous fashion, we propose the term “pseudoschizogeny” for this type of development. Unusual, or perhaps unique, features of this cavity: bicellular condition, protoplast retraction from the common shared wall, and deposition of a callose wall. Preliminary results of a survey of Eupatorium show that bicellular cavities are uncommon but widely distributed geographically.     

Secretory Cavity Development and Its Relationship with the Accumulation of Essential Oil in Fruits of Citrus medica L. var. sarcodactylis （Noot.） Swingle

The developmental types of secretory cavities in Citrus remain controversial. The relationship between secretory cavity development and the accumulation of essential oil in fruits of Citrus species is also unknown. In order to develop better insights into these problems, histological, histochemical, and cytochemical methods were used to investigate secretory cavity development and the accumulation of essential oll at different developmental stages of fruits of Citrus medica L. var. sarcodactylis （Noot.） Swingle. The results indicate that the secretory cavity of the variety seemed to originate from an epidermal cell and a subepldermal cell. These two cells underwent successive divisions, resulting In the formation of two parts： （Ⅰ） a conical cap; and （Ⅱ） a globular gland. The formation of the lumen was schlzolysigenous. Regular changes in the size of vacuoles and the accumulation of essential oil were revealed during the process of secretory cavity development. In addition, when fruits were a light yellow or golden color, the structure of secretory cavities was well developed and the content of essential oil in a single fruit reached a maximum. It would be most appropriate to collect the fruit as a medicinal material at this time.     

Structure and development of the secretory cavities of Myrtus communis leaves

The structure and development of Myrtus communis L. secretory cavities has been studied in young and expanded leaves, using light and scanning electron microscope. Secretory cavities are continuously formed during leaf development, but in mature leaves the rhythm of their appearance shows steep decrease. Each secretory cavity is developed from a single epidermal cell, which undergoes a periclinal division followed by anticlinal and several oblique cell divisions. The lumen of the secretory cavity is initiated by cell wall separation, i.e., schizogenously. The secretory cells line the cavity, where the secreted material is collected. Secretory cavities are covered by modified epidermal cells, which do not seem to form any special aperture. Essential oils seem to be discharged after mechanical treatment of the leaf.     

COMPARATIVE DEVELOPMENT OF SECRETORY CAVITIES IN THE TRIBES AMORPHEAE AND PSORALEEAE (LEGUMINOSAE: PAPILIONOIDEAE)

The tribes Amorpheae and Psoraleeae of the Leguminosae (Papilionoidae) share the characteristics of one-seeded fruits and gland-dotted foliage. Because of this, they traditionally have been considered closely related (either a single tribe or two closely related tribes). However, Barneby (1977) has suggested that the Amorpheae and Psoraleeae are not close but previously had been combined on the basis of a superficial resemblance. This paper describes the structure of the secretory cavities responsible for the gland dots. Approximately 50% of the species of each tribe were surveyed for cavity structure with leaflet clearings. Eight species were then chosen for developmental studies of their glands. Several distinct kinds of secretory cavities are present in these plants. Trabeculate cavities (found only in the Psoraleeae) are traversed by many elongated cells. This type of cavity and nontrabeculate cavities of the Psoraleeae initiate with localized dorsiventral elongation of protodermal cells to form a hemispherical protuberance on the leaf primordium surface. Development proceeds with separation of the cells of a protuberance along their lateral walls facing the protuberance center. As the leaf expands, the protuberance sinks until its apex is flush with the leaf surface. The result is a cavity lined by an epithelium of modified epidermal cells. Trabeculate cavities have more cells in the initial protodermal bump than nontrabeculate “epidermal” cavities, and the central cells of the protuberance are not involved in epithelium formation, but become separated from other cells on all lateral sides, transversing the cavity as trabeculae. Cavities of the Amorpheae are all nontrabeculate and subepidermal. They initiate with periclinal divisions of protodermal cells that result in two cell layers. The exterior layer differentiates into epidermis, while the interior layer divides to produce a small spherical group of cells (“epithelial initials”). Schizogeny occurs in the center of these cells to produce an epithelium-lined cavity. Previous studies of cavity development in the Amorpheae described lysigenous and schizo-lysigenous cavities for most species. These early reports are reviewed, and the possible role of preparation artifacts in producing images of lysigenous development in general is discussed.     

DEVELOPMENT OF CHAMBERED PITH IN STEMS OF PHYTOLACCA AMERICANA L. (PHYTOLACCACEAE)

An integrated microscopic (light and electron microscopy) and macroscopic investigation of chambered pith development was made of Phytolacca americana L. Terminal internodes have a solid pith cylinder in contrast to the alternating diaphragms and chambers occurring in subjacent pith. Macroscopically, chambers and diaphragms of any one internode are of equal size. Microscopically, diaphragms vary in height within an internode (from 1–6 cells high). Nevertheless, all diaphragms become thicker circumferentially (5–12 cells high) and connect with long files of intact peripheral pith cells. Diaphragm cells have a large centrally positioned vacuole with a thin, parietal layer of cytoplasm; nuclei, mitochondria, endoplasmic reticulum, and unidentified organelles differentiate in the cytoplasm of diaphragm cells. Although schizogenous activity has most often been implicated as the mechanism by which chambered pith develops in vegetative organs of angiosperms, the results of this study show that cavities in pokeweed result from both schizogenous and lysigenous mechanisms. Schizogeny is suggested by the fact that central pith cells of terminal internodes are longer and thinner walled than peripheral pith cells arranged in vertical files, thus indicating elongation of cells as a possible result of internode elongation. The precise developmental pattern and arrangement of chambers and diaphragms also suggest schizogenous processes. Lysigenous or enzymatic activity is indicated by the fact that cavities are bounded by broken cells, and wall fragments and organelles are often found within enlarging cavities. Chamber formation occurs continuously acropetally and centrifugally in the central pith. A comparison of diaphragms is made with Liriodendron tulipifera and Juglans nigra in an attempt to resolve differences in structure and terminology regarding the differentiation of chambered and diaphragmed pith.     

ULTRASTRUCTURAL DEVELOPMENT OF CAPITATE GLANDULAR HAIRS OF CANNABIS SATIVA L. (CANNABACEAE)

The capitate-sessile and capitate-stalked glands of the glandular secretory system in Cannabis, which are interpreted as lipophilic type glandular hairs, were studied from floral bracts of pistillate plants. These glands develop a flattened multicellular disc of secretory cells, which with the extruded secretory product forms the gland head and the auxiliary cells which support the gland head. The secretory product accumulates beneath a sheath derived from separation of the outer wall surface of the cellular disc. The ultrastructure of secretory cells in pre-secretory stages is characterized by a dense ground plasm, transitory lipid bodies and fibrillar material, and well developed endoplasmic reticulum. Dictyosomes and dictyosome-derived secretory vesicles are present, but never abundant. Secretory stages of gland development are characterized by abundant mitochondria and leucoplasts and by a large vacuolar system. Production of the secretory product is associated with plastids which increase in number and structural complexity. The plastids develop a paracrystalline body which nearly fills the mature plastid. Material interpreted as a secretion appears at the surface of plastids, migrates, and accumulates along the cell surface adjoining the secretory cavity. Extrusion of the material into the secretory cavity occurs directly through the plasma membrane-cell wall barrier.     

吴茱萸果实中分泌囊的发生和发育研究

吴茱萸果皮内分布有许多分泌囊。我们作了发育解剖学方面的研究。在花蕾期,雌蕊的子房中分泌囊原始细胞即开始发生,它起源于单个表皮细胞和其内的1—4层薄壁细胞。分泌囊最初为裂生,后期由于上皮细胞的破毁,其腔隙逐渐扩大,因此,腔隙发生方式应属裂溶生型。成熟分泌囊是由多层鞘细胞和上皮细胞包围圆形腔隙构成。     

Studies on the Structure and Development of Secretory Cavities in Poncirus Trifoliata

Light microscopical observation of thin sections revealed that the initials of secretory cavities in Poncirus trifoliata (L.) Raf. originated from parenchyma cells below the epidermis in early stages of development. The cavity lumen appeared in the center of the initials and gradually enlarged during subsequent development. Concurrently the ceils surrounding the central space differentiated into secretory cells and sheath cells. The developed cavities of fruit ,stem and leaf consisted of 2–5 layers of sheath cells and 2–3 layers of secretory cells surrounding a spherical space. The secretory cells lining the space were observed to remain intact throughout the plantt s life. On the basis of comparative studies with the aid of different kinds of fixatives, embedding media and sectionings,it was suggested that the ,manner of formation of the lacunao of secretory cavities in fruit peels of P. trifoliata, Citrus reticulata and C. sinensis were different. However,as seen in thin sections the secretory cavities of all the 3 species developed schizogenously. Our result with reference to views of other authers concluded the existance of a common schizogenous cavity formation in Rutaceae.     

Ultrastructural studies on the secretory cavities ofCitrus deliciosa ten. II. Development of the essential oil-accumulating central space of the gland and process of active secretion

Summary Oil glands ofCitrus deliciosa are multicellular secretory structures, globular to oval in shape, in the centre of which an essential oil-accumulating space is formed. Opening of this space begins from a single cell. It undergoes lysis which later extends to the neighbouring gland cells.Secretory material in form of droplets is produced in plastids, from where it is transported to the parietal cytoplasm of the secretory cells via numerous ER-elements. After fusion of the ER-membranes with the plasmalemma, the exudate reaches the apoplast, through which it is driven to the central cavity of the gland.Peripheral cells of the secretory complex are modified into a protective sheath with thick walls and large vacuoles, while their plastids are differentiated from leucoplasts into typical amyloplasts.     

中国芸香科植物叶分泌囊比较解剖学研究

利用整体透明、石腊和薄切片方法对芸香科22属,40种和2变种植物叶分泌囊的形态结构和分 布进行了比较研究。成熟分泌囊都由鞘细胞和一层上皮细胞围绕圆形腔隙构成,上皮细胞扁平,细胞壁 薄、完整,故分泌囊属裂生方式发生。鞘细胞1～5层,不同种类的层数有变化,个别种缺乏。内层鞘细 胞为扁平的薄壁细胞,外层的细胞壁较厚。分泌囊的形态结构、着生位置和分布密度等在不同属或不同 种间存在一定差异。根据分泌囊在叶中的分布位置和形态结构特点,可将其划分为:叶缘齿缝分泌囊, 叶肉分泌囊和两者混合型。叶肉分泌囊又可分海绵组织分泌囊和栅栏组织分泌囊。在此基础上对该科各类型分泌囊的形态演化关系以及各亚科或各属间的亲缘关系进行了探讨。     

Age-dependent changes in ultrastructure of the defensive glands of Neocapritermes taracua workers (Isoptera,Termitidae)

Protection against predators and competitors is one of the main concerns of termite colonies, which developed a specialised defensive caste, the soldiers. However, soldiers are rare or even missing in several lineages of termites, while workers often develop new defence strategies especially in soil-feeding species. Here, we describe the morphology and ultrastructure of the autothysis-associated glands of Neocapritermes taracua workers and report their age-related changes in structure. The defensive glands of N. taracua workers consist of a pair of labial and a pair of crystal glands, whose secretions mix together through autothysis. Autothysis always occurs at the line of weakness connecting the anterior parts of the crystal-bearing pouches. The crystal glands consist of groups of bicellular secretory units (secretory and corresponding canal cells) which secrete the blue crystal material into external pouches. Their secretory activity is maximal in the middle of worker life, and is considerably lower in very young and old workers. The labial glands are composed of two types of secretory cells: the central and the parietal cells. While the central cells are developed similarly to other termites and secrete proteinaceous secretion into labial gland ducts, the parietal cells develop proteinaceous granules which may eventually bud off the cells. The secretory function of parietal cells is so far unique to N. taracua and differs from other termite species in which they are only responsible of water uptake by acini. The defensive device of N. taracua is truly exceptional as it involves a new gland and a previously undescribed function for parietal cells, being a remarkable example of evolution of morphological innovation.     

Developmental Ultrastructure of Glandular Trichomes of <Emphasis Type="Italic">Rosmarinus officinalis</Emphasis>: Secretory Cavity and Secretory Vesicle Formation

Glandular trichomes in the leaf lamina of Rosmarinus officinalis L. were examined by scanning and transmission electron microscopy. The leaves were characterized by an abundance of two types of glandular trichomes—small capitate and large peltate glandular trichomes. In addition to the glandular trichomes, numerous non-glandular trichomes were present on the abaxial surface of the leaf. These trichomes mainly predominated on the midrib, whereas glandular trichomes occurred on non-vein areas. At the initial phase of secretory cavity formation, hyaline areas were abundant in periclinal walls of head cells, while they were not observed in the anticlinal walls. The hyaline areas gradually increased in size, fusing with other areas throughout the wall. Loose wall material adjacent to hyaline areas was released from the head cell walls and migrated into the secretory cavities. As the secretory cavities continued to enlarge, the new vesicles emerging into the secretory cavities from the walls of head cells became surrounded with the surface of a typical membrane. They developed a round shape, but the contours of the vesicle surfaces appeared polygonal when tightly packed inside a cavity. These vesicles varied in size; small vesicles often possessed electron-dense contents, while large vesicles contained electron-light contents.     

Morphology and distribution of cystic cavities in the normal murine thymus

Summary The normal murine thymus was examined by lightand electron microscopy to determine the distribution and morphology of extracellular cystic cavities. Most cavities were confined to the cranial half of each gland, situated at the junction between cortex and medulla. They varied in size and shape, and gave rise to narrow channels that coursed to the capsular surface of the gland. Large cavities could be divided into three zones. A short cranial zone exhibited gland-like features, consisting of cells lining a clear lumen. A central zone was lined by a diverse population of cells. Some possessed secretory granules, while others exhibited an apical ciliated border. Lining cells interdigitated with each other and were joined laterally by intercellular junctions. The lumen of the central zone contained lymphocytes and macrophages in an amorphous extracellular matrix. The caudal zone of each cavity had an attenuated and incomplete cellular lining, communicating directly with the surrounding thymic parenchyma. Thymic cavities may represent the initial part of the efferent lymphatic system of the gland, beginning in the tissue spaces at the corticomedullary junction. Selected cells could then enter and interact with the luminal contents in the central zone of the cavity. Ciliated cells may then propel lymphocytes and secretions into the narrow channels radiating from the uppermost part of the chamber, leaving a cell-free lumen in this region. These cavities may function in sequestering lymphocytes, macrophages and thymic secretions before their exit from the gland.     

SOME ASPECTS OF SIEVE CELL ULTRASTRUCTURE IN PINUS STROBUS

The immature sieve cell of Pinus strobus contains all of the protoplasmic components commonly encountered in young cell types. In addition, it contains slime bodies with distinct double-layered limiting membranes. The mature sieve cell is lined by a narrow layer of cytoplasm consisting of a plasmalemma, one or more layers of anastomosing tubules of endoplasmic reticulum, numerous mitochondria, starch granules and crystal-like bodies. Each mature cell contains a necrotic nucleus. Ribosomes and dictyosomes are lacking. Strands derived ontogenetically from the slime bodies of the immature cell traverse the central cavity and are continuous with those of neighboring sieve cells through the plasmalemma-lined pores of the sieve areas. Sieve-area pores are also traversed by numerous endoplasmic membranes. A membrane was not found separating the parietal layer of cytoplasm from the large central cavity.     

Programmed cell death of secretory cavity cells in fruits of Citrus grandis cv. Tomentosa is associated with activation of caspase 3-like protease

Previously, we found that secretory cell degradation typically occurred through programmed cell death during secretory cavity development in Citrus sinensis L. (Osbeck). This finding indicated that secretory cavities could be utilized as a new cell biology model for investigating the regulatory mechanisms of plant programmed cell death. To study further the programmed cell death during secretory cavity development in Citrus fruit, we studied the morphogenetic characteristics of secretory cavities during their development in Citrus grandis cv. Tomentosa. Using light microscope- and electron microscope-TUNEL assays, immunohistochemistry and immunocytochemistry, we described the precise spatial and temporal alterations in caspase 3-like distribution, chromatin condensation and DNA fragmentation during the programmed cell death of secretory cavity cells. Caspase 3-like was found to be significantly located in both the cytoplasm and the nucleus of secretory cavity cells undergoing programmed cell death, and caspase 3-like is closely associated with chromatin condensation and DNA fragmentation. Interestingly, both caspase 3-like and DNA fragmentation were detected in the nucleoli. Our findings suggest that caspase 3-like may be involved in the programmed cell death of secretory cavity cells, especially in chromatin condensation, DNA fragmentation, nuclear degradation and the degradation of certain organelles.     

芸香科植物茎分泌囊的研究

利用石蜡切片和薄切片方法对芸香料１４属２３种和１变种植物幼茎中分泌囊的分布和结构进行了比较研究。在芸香科植物茎中,靠近表皮的皮层中分布一轮分泌囊,分泌均由鞘细胞和一层上皮细胞围绕圆形腔隙构成,上皮细胞扁平,细胞壁薄,完整。鞘细胞１－５层。在不同亚科、不同属之间,分泌囊的差异仅仅表现在分泌腔的大小和鞘细胞的层数方面。一般草本类型属植物     

生姜根茎的发育过程及分泌腔的超微结构

为了解生姜(Zingiber officinale Roscoe)根茎的发育过程,在光学显微镜和电子显微镜下对不同发育时期的生姜进行显微和超微结构观察,并对分泌腔的发生发育过程进行了研究。结果表明,幼嫩期的生姜,表皮以内的基本组织可大致分为皮层、拟内皮层和中柱。次生加厚分生组织起源于中柱外侧一些细胞,细胞分裂和体积增大促使生姜发育。薄壁细胞内有大量的淀粉粒且其数量、形状和大小因发育时期而不同。分泌腔广布于生姜中,其发育过程可分为3个阶段:分泌腔原始细胞团形成、分泌腔的发生和成熟分泌腔形成。生姜精油主要在线粒体、质体和细胞质中合成。本研究为生姜药用资源的开发利用提供了理论依据。     

Observations on the development of the foliar secretory cavities of Porophyllum lanceolatum (Asteraceae)

The lipophilic secretory cavities observed in the leaf of Porophyllum lanceolatum (Asteraceae) are scattered throughout the lamina and around its crenate margins. In the young leaf the cavities are initiated, and their development completed, while the surrounding tissues are still at early stages of differentiation. The cavity lumen has a lysigenous origin. Cell lysis, expansion of the developing leaf and, probably, the pressure exerted by the accumulation of secretory products, are believed to account for the gradual enlargement of the lumen. Concomitantly with ctll disintegration, which occurs throughout development, divisions take place in all cells of the gland. A mature cavity has a multilayered epithelium. Histochemical tests for RNA, proteins, phenolics and pectic polysaccharides revealed intense staining of the content of the epithelial cells in the early stages of cavity development, and a decrease in staining towards its maturity. Staining for lipids is intense in all developmental stages. Tests on the material observed in the lumen of mature cavities, show positive results for lipids, pectic polysaccharides and phenolics.     

Peculiar salivary glands in a silk‐producing mite Bakericheyla chanayi (Cheyletidae)

This is the first ultrastructural investigation of salivary glands in the family Cheyletidae. In both sexes of Bakericheyla chanayi, paired acinous salivary glands and tubular coxal glands were shown to be united into the common podocephalic system. The secretory portion of the salivary gland includes medial and lateral lobes composed of the five and two cells, respectively, with clearly distinct ultrastructure. The cytoplasm of the cells is occupied by the secretory granules containing fine fibrous material. The fine structure of both cell types suggest a proteinaceous nature of their secretions. A single central process extending from the apical face of each secretory cell passes through the common acinar cavity to enter the conducting duct. A pair of intercalary cells at the base of the conducting duct links it with the secretory portion of the gland. Extending towards the acinar cavity, protrusions of intercalary cells alternate the apical regions of the secretory cells and form with them highly‐specialized contacts characterized by the apical network of microtubules and microfilaments. Two possible ways of secretion are suggested: 1) exocytosis into the acinar cavity and 2) direct passage via the central processes. The detection of axon profiles in the gland body suggests a neural control for the glandular cell function. In tritonymphs, neither secretion nor large lateral lobe cells were observed up to the pharate stage when the lateral lobe undergoes rapid differentiation. The arrangement of the acinous gland is compared to that of other arthropods. Its composition appears to be close to the class three of insect glands. The involvement of the lateral lobe cells in silk production is discussed. J. Morphol. 276:772–786, 2015. © 2015 Wiley Periodicals, Inc.