Electron microscopy of gas space (aerenchyma) formation in adventitious roots of Zea mays L. subjected to oxygen shortage

This paper examines the ultrastructure of cortical cells in maize root tips during the early stages in lysigenous aerenchyma formation, promoted by oxygen-deficient nutrient solution. The aim was to determine whether changes in fine structure were compatible with oxygen starvation as the primary cause of cell degeneration and death. There was an initial collapse of some cortical cells, indicating loss of turgor, and the cytoplasm became more electron dense. Mitochondria and endoplasmic reticulum appeared normal at this early stage though the tonoplast lost its integrity. Subsequently the cytoplasm became less electron dense than surrounding healthy cells, and underwent further degeneration while the plasmalemma retracted from the cell wall. Cell walls remained unaltered until this stage, but some then became thin and electron transparent. No cells of the stele were found to degenerate. These observations, which do not readily accord with the hypothesis that oxygen starvation was the cause of cell death, are compared with detailed studies of cell degeration in other cell types. An alternative mechanism for the stimulation of cortical cell lysis in poorly oxygenated roots involving the hormone ethylene, is discussed.     

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。     

Ultrastructure of the Resin Ducts of Mangifera indica L. (Anacardiaceae). 1. Differentiation and Senescence of the Shoot Ducts

A detailed electron microscope study has led to the conclusionthat the resin ducts of the shoot of Mangifera indica L. developlysigenously. This study has also established several characteristicswhich can serve as criteria for a clear distinction betweenschizogenous and lysigenous cavities. The main characteristicsof lysigenous cavities are: (1) The presence of disorganized cytoplasm in the duct cavity. (2) The presence of wall remains attached to the wall of livingepithelial cells facing the cavity. (3) The presence of specific intercellular spaces at the cellcorners facing the duct lumen. Duct development starts with the disintegration of a file ofcells forming an initial cavity. Later the cells lining thiscavity differentiate into cells secreting lipophilic compounds.As a result of growth and differentiation of the tissues aroundthe duct, its lumen becomes compressed and comes to resemblea branched narrow slit. Such a slit may wrongly be regardedas an initial stage of a schizogenous duct. Disintegration ofepithelial cells occurs throughout all stages of development.Neighbouring cells partly fill the space which is released bydisintegrating cells. At the end of the stage of secretion thecytoplasm of all epithelial cells darkens, preceding their disintegration.This darkening is a gradual process which begins in the vicinityof ribosomes. When all dark epithelial cells disintegrate thecavity widens and the neighbouring parenchyma cells substitutefor the secretory epithelium without undergoing any significantchange in their cytoplasm. Mangifera indica L., mango, resin ducts, ultrastructure     

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.     

Glandular scale development and essential oil secretion in Origanum dictamnus L.

Glandular scales of Origanum dictamnus L. originate from a single protodermal cell. They are composed of a 12-celled head and an unicellular stalk and foot. During the early stages of gland differentiation, the head cells possess a small number of plastids which contain globular inclusions. Similar inclusions are also observed in the plastids of the stalk and the foot cell. The lateral walls of the stalk cell progressively undergo cutinization which does not extend to the upper and lower periclinal walls. At the onset of secretion the electron density of the plasmalemma region lining the apical walls of the head cells remarkably increases. These walls are impregnated with an osmiophilic substance identical in appearance to the content of the subcuticular space. In a following stage of the secretory process osmiophilic droplets of various size arise in the cytoplasm of the secretory cells which undergoes simultaneously a reduction of its initial density. After secretion has been concluded the protoplast of the head cells becomes gradually degenerated. The chlorenchyma cells of the mesophyll possess numerous microbodies closely associated with various organelles. In the cytoplasm of these cells crystalloids occasionally occur.     

ULTRASTRUCTURAL EVIDENCE FOR SECRETORY PHASES IN THE LIFE HISTORY OF STIGMATIC HAIRS OF COTTON: A DRY TYPE STIGMA

Stigmatic hairs of the cotton flower were studied through their developmental stages up to anthesis. Stigmatic hairs invariably develop from a densely straining band of epidermal cells opposite the transmitting tissue cells. At anthesis, these are single cell structures measuring up to 300 μm long. At the 5-mm stage of stylar length (7–10 days before anthesis), some stigmatic hair cells begin to accumulate an osmiophilic substance between the plasmalemma and the cell wall, possibly synthesized in the endoplasmic reticulum. This material is apparently never secreted outside the cell wall. Immediately following this secretory phase in some stigmatic hair cells a second secretory phase starts. A dense osmiophilic substance, different in appearance from the previous phase, accumulates in the vacuoles of each hair cell. Concomitantly, dimorphism develops in the cytoplasmic densities of stigmatic hair. Some stigmatic hair cytoplasm appears very dense and shows signs of degeneration while other cytoplasm appears normal. A third secretory phase, which begins at anthesis, occurs in the normal hair cells. This phase is characterized by enhanced activity in the cytoplasm of the endoplasmic reticulum and Golgi apparatus. Large vesicles containing granular material are seen fusing with the plasmalemma. Coincident with this activity there is dissolution of the middle layers of the cell wall and the cuticle is ruptured at various points. The dense osmiophilic substance that had accumulated in the vacuole breaks down into fine granular material. Significance of these changes is discussed in relation to the pollen germination mechanism on the dry type stigma of cotton.     

The role of the parenchyma sheath and PCD during the development of oil cavities in Pterodon pubescens (Leguminosae-Papilionoideae)

Pterodon pubescens cavities are constituted by lumen and uniseriated epithelium surrounded by multiseriate parenchyma sheath. We studied the development of secretory cavities, including the role of parenchyma sheath, using light and transmission electron microscopy. A Tunel assay was performed to verify whether programmed cell death (PCD) occurs during the process. The lumen is formed by schizogeny and lysigeny occur in later developmental stages of the secretory cavities. Ultrastructurally, epithelial cells in later developmental stages become dark and with sinuous walls; the protoplast becomes retracted and the cytoplasm shows low organelle definition. Degenerated cells are released toward the lumen. Our results showed that PCD occurs during later developmental stages of cavities and plays a critical role in functioning of these glands. New cells originated from the parenchyma sheath differentiate into secretory cells and replace those degenerated ones. This fact associated to PCD guarantees epithelium renovation during the secretory cycle and the maintenance of secretory activity of cavities.     

ULTRASTRUCTURE OF GLANDULAR TRICHOMES OF LEAVES OF NICOTIANA TABACUM L., cv XANTHI

Electron microscopy confirms previous light microscope observations that tobacco leaf trichomes are glandular and that there are two different types. Both the tall trichome (multicellular stalk, unicellular or multicellular head) and the short trichome (unicellular stalk; multicellular head) exhibit characteristics common to gland cells—a dense cytoplasm, numerous mitochondria, and little vacuolation. The tall trichome contains structurally well developed chloroplasts and an elaborate network of endoplasmic reticulum. The short trichome contains undifferentiated plastids and endoplasmic reticulum which parallels the nucleus and plasmalemma. Few dictyosomes are seen either in the short trichome or in the tall trichome. The short trichome appears to undergo structural changes concurrently with the appearance of secretory product within the cells. The most noticeable change is the formation of the extraplasmic space between the cell wall and the plasmalemma. Electron dense secretory product is observed between the plasmalemma and the cell wall and within the intercellular spaces.     

The development and ultrastructure of gum ducts inCitrus plants formed as a result of brown-rot gummosis

Summary Young stems ofCitrus plants were infected with the fungusPhytophthora citrophthora. The effect of the infection on gum duct development was studied. The following sequence of structural changes was observed in the cambial zone: 1. The middle lamellae between layers of xylem mother cells dissolve forming duct cavities. 2. The cells around the duct cavities differentiate into epithelial cells rich in cytoplasm. 3. The amount of Golgi bodies and associated vesicles increases. The vesicles and small vacuoles, some of which seem to originate from the fusion of Golgi vesicles, contain fibrillar material that stains for polysaccharides. Vesicles and vacuoles appear to fuse with the plasmalemma. Material staining positively for polysaccharides accumulates between the plasmalemma and cell wall, and penetrates the latter. 4. The protoplast shrinks and the space below the cell wall, which contains polysaccharides, increases in volume. 5. After a period of 10 days or more the gum ducts become embedded in the xylem, and the activity of the epithelial cells ceases. The cell walls of many of them break, and the gum still present in the cells is released.     

The Structure of the Canal Cell in the Style of Lilium regale

The fine structure of canal cell in the style of Lilium regale has been observed under light and electron microscopes by OMA thin section method and ultra-thin section method respectively. The ultrastructural specialization of the canal cells during their functional stages may be characterized as follows: 1. The cell wall on the secretory face of the canal cell has numerous branched ingrowths extending into the cytoplasm, and the plasmalemma closely follows the contours of the ingrowths to form the wall-membrane apparatus. This pattern of distribution of plasmalemma increases the surface-volume ratio of the cell to facilitate the secretion of solutes out of the cell. 2. The cell wall under the thin layer of cuticle on the outside of the secretory face is digested starting from the outer part and gradually extending to the inner part to form a large space, the temporary secretory layer. During the secretion of products by the cell, the thin layer of cuticle becomes ruptured in many places and finally disappeared. Therefore the cell wall of the secretory face remains a thin layer only at that time. The change of the layers of the cell wall is involved in the mechanism of cell secretion. 3. The ultrastructural characteristics of the canal cell indicate that this cell is active in synthesis, intercellular transport and energyn metabolism. Some of the major facts seen in all cases included the highly lobing of nucleus, abundance of endoplasmie reticulum throughout the cytoplasm and well developed mitochondria, dictyosomes and polysomes. During the secretory stage of the cell, mitochondria apparently concentrate near the wall-membrane apparatus. 4. There are numerous granular and vesicular structures near the wall-membrane apparatus on the secretory face, especially at the space between wall ingrowths and plasmalemma. The presence of these granular and vesicular structures is thought to be related to the secretory function of the cell. According to the specialized characteristics the canal cell is evidently a typical transfer cell of the secretory type.     

薄荷头状腺毛分泌过程的超微结构研究

电镜观察表明,刚形成的薄荷头状腺毛的头部细胞,细胞核较大细胞质浓,有一些小液泡,质体和线粒体最显著,分泌前期,内质网及高尔基体数量明显     

On the ultrastructure of differentiating secondary xylem in willow

Summary Studies of differentiating xylem inSalix fragilis L. show the immediate cambial derivatives to be ultrastructurally similar. The Golgi apparatus is important at all stages of wall synthesis, possibly producing (amongst other substances) hemicellulose material which is carried to the wall in vesicles or multivesicular bodies. The endoplasmic reticulum also contributes one or more components to the developing wall: at some stages during differentiation the endoplasmic reticulum produces electron opaque bodies which appear to be guided towards the wall by microtubules. Compact structures formed from concentric membranes (myelin-like bodies) have been found joined to rough endoplasmic reticulum, but their presence is not explained.Two types of plasmalemma elaboration occur: invagination of the plasmalemma itself to form vesicles which may contain cytoplasmic material; and vesicles between the plasmalemma and cell wall which are the result of single vesicles or multivesicular bodies traversing the plasmalemma. Both systems provide a means for transporting cytoplasmic material across the plasmalemma.Microtubules have been seen associated with all vesicles derived from the cytoplasm which appear to be moving towards the wall. The presence of microtubules may generally be explained in terms of orientation of vesicles, even if they also happen coincidentally to parallel the supposed orientation of microfibrils in the wall itself. It is possible to resolve connections between the microtubules and the plasmalemma.     

杭白芷根的分泌道超微结构与其挥发油分泌的关系

利用光镜及透射电子显微镜技术研究了杭白芷根中分泌道结构及其挥发油的分泌,并重点探讨分泌道中挥发油的分泌过程。结果显示:(1)杭白芷的分泌道是由上皮细胞围绕着的伸长的胞间隙,腔道内贮存着挥发油。(2)分泌道细胞的质体、细胞基质以及线粒体参与挥发油或其前体物质的合成。(3)在分泌道发育的后期,大量小泡与分泌细胞的液泡膜和细胞质膜融合,将其内的物质释放进入空腔。研究认为,杭白芷分泌道中挥发油主要合成部位为质体及细胞基质,之后以扩散渗透或通过膜质小泡与液泡及质膜融合这两种方式分泌到空腔内,丰富的线粒体可能为这一系列过程提供能量。     

Unusual transfer cells in the epithelium of the nectaries ofAsclepias curassavica L.

Summary The secretory cells of the nectaries ofAsclepias curassavica form a glandular epithelium in the inner parts of the stigmatic chambers. They resemble transfer cells in having many infoldings of the plasmalemma. The wall protuberances, however, are poorly developed and often lacking. The plasmalemma is highly convoluted and forms, in places, external compound membranes where the extracytoplasmic space is collapsed completely. Active glands contain dilated cisternae of the ER and large vesicles which are mainly associated with the cis face of the dictyosomes. In addition, small vesicles are observed in high number. It is discussed whether the secretion is granulocrine or eccrine and whether the enlargement of the plasmalemma is the cause or the consequence of the high secretory activity. After the secretory phase the outer peripheral part of the cytoplasm disintegrates. The remaining part of the protoplast is covered by a new plasmalemma.     

鹅掌楸油细胞的发育解剖学研究

鹅掌楸油细胞比相邻组织细胞分化,因而在叶肉细胞未完全分化的叶原基、幼叶以及未完全分化的幼茎中,都可看到已分化的油细胞。通常,在第二叶原基中可发现油细胞原始细胞,由于其染色深、细胞核大而易与周围组织的细胞相区别。以后,油细胞逐步液泡化,直至形成一个大的液泡,此时,细胞核呈扁平状,并与细胞质一起成为一薄层围绕着大液泡。当油细胞发育成熟后,细胞质及核开始解体,整个油细胞的腔由大液泡充满,成为油囊,在部分     

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.     

Electron microscope investigation of sieve-element ontogeny and structure inUlmus americana

Summary During advanced stages of sieve-element differentiation inUlmus americana L., dispersal of the P-protein (slime) bodies results in formation of a peripheral network of strands consisting of aggregates of P-protein components having a striated, fibrillar appearance. The tonoplast is present throughout the period of P-protein body dispersal. Perforation of the sieve plates is initiated during early stages of P-protein body dispersal.Small P-protein bodies consist of tubular components, most of which measure about 180 Å in diameter. With increase in size of the P-protein bodies narrower components appear. At the time of initiation of P-protein body dispersal, most of the components comprising the bodies are of relatively narrow diameters (most 130–140 Å) and have a striated, fibrillar appearance. Both wide and narrow P-protein components are present throughout the period of sieve-element differentiation and in the mature cell as well, and a complete intergradation in size and appearance exists between the two extremes. Both extremes of P-protein component have a similar substructure: an electron-transparent lumen and an electronopaque wall composed of subunits, apparently in helical arrangement. The distribution of P protein in mature sieve elements was quite variable.The parietal layer of cytoplasm in matureUlmus sieve elements consists of plasmalemma, endoplasmic reticulum cisternae in two forms (as a complex network closely applied to the plasmalemma and in stacks along the wall), mitochondria, and plastids.     

Development,structure, and occurrence of secretory trichomes ofPharbitis

Summary Secretory trichomes develop from epidermal cells on the leaf primordia and stem ofPharbitis nil. Following an initial growth phase, trichomes begin active secretion of a protein-carbohydrate mucilage. This mucilage covers the shoot apex and developing leaves ofPharbitis.The secretory cells possess cellular organelles in forms usually associated with actively secreting cells: many mitochondria, an elaborate network of rough endoplasmic reticulum (RER), many free ribosomes, and numerous dictyosomes. The role of the dictyosomes is twofold: 1. dictyosome vesicles bud coated vesicles which transport materials from the cell and, 2. dictyosome vesicles coalesce, forming large storage vesicles. The storage vesicles are surrounded by, and often in contact with, poculiform RER. The RER forms an interconnected network throughout the cytoplasm, extending from the nuclear envelope to the plasmalemma. Distended profiles of RER are frequently in direct contact with the plasmalemma. Thus, inPharbitis secretory trichomes, it is the coated vesicles and RER which are active in secretion export. These findings imply a secretory pathway which deviates from the usual pattern in glandular cells.Predoctoral fellow of National Science Foundation during part of the investigation.     

Dorsal-ventral differentiation in Simonsiella and other aspects of its morphology and ultrastructure

The morphology and ultrastructure of the aerobic, Gram-negative multicellular-filamentous bacteria of the genus Simonsiella were investigated by scanning and transmission electron microscopy. The flat, ribbon-shaped, multicellular filaments show dorsal-ventral differentiation with respect to their orientations to solid substrata. The dorsal surface, orientated away from the substrate, is convex and possesses an unstructured capsule. The ventral surface, on which the organisms adhere and glide, is concave and has an extracellular layer with fibrils extending at right angles from the cell wall. The cytoplasm in the ventral region contains a proliferation of intracytoplasmic membranes and few ribosomes in comparison to the cytoplasm in other parts of the cell. Centripetal cell wall formation is asymmetrical and commences preferentially in the ventral region. Quantitative differences in morphology and cytology exist among selected Simonsiella strains. Functional aspects of this dorsalventral differentiation are discussed with respect to the colonization and adherence of Simonsiella to mucosal squamous epithelial cells in its ecological habitat, the oral cavities of warm-blooded vertebrates.List of Abbreviations SEM scanning electron microscope - TEM transmission electron microscope     

Programmed cell death during pigment gland formation in Gossypium hirsutum leaves

Ultrastructural studies have shown that the formation of pigment glands in Gossypium hirsutum L. leaves is a lysigenous process, originating from a cluster of cells in the ground meristem. Various techniques were used here to investigate whether programmed cell death (PCD) plays a critical role in this developmental process. Nuclei of internal cells in the pigment gland‐forming tissue were TUNEL‐positive and DAPI‐negative, suggesting that DNA cleavage is an early event and complete DNA degradation is a late event. Smeared bands and a lack of laddering after gel electrophoresis indicate that DNA cleavage is random. Ultrastructurally, secretory cells in the pigment glands become distorted, nuclei are densely stained, and chromosomes become condensed until completely degraded at late stages. Vacuoles with electron‐dense bodies and membrane‐bound autophagosomes are seen in both secretory and sheath cells, suggesting that autophagy plays a key role in PCD during cytoplasm degradation. Buckling of cell walls, seen at early stages, later leads to a complete breakdown of the walls. Together, these results suggest that PCD plays a critical role in the lysigenous development of pigment glands in G. hirsutum leaves.