Development Of Organelles Research Articles

The ultrastructure and cytochemistry of the egg apparatus of Brassica campestris

The egg apparatus of Brassica campestris L. cv. Candle (canola-rapeseed) is composed of an egg and two synergids juxtaposed at the extreme micropylar end of the megagametophyte with the egg cell displaced in a chalazal direction. The cell walls of the synergids and egg are uniformly PAS and PA–TCH–SP-positive, but contained β-linked glucans only in the micropylar region. The number and development of the cytoplasmic organelles suggested that the egg cell is relatively inactive metabolically while the synergid cells are active. The synergids contain large numbers of dictyosomes with PA–TCH–SP-positive vesicles at the maturing face. These vesicles appear to fuse with the plasma membrane in the region of the filiform apparatus. The filiform apparatuses of the synergids are micropylar finger-like projections that extend into the cytoplasm of the synergid. These are PAS and PA–TCH–SP-positive, fluoresce in uv light when stained with Calcofluor, and show a positive response for acidic polysaccharides when stained with alcian blue. After treatment with cellulase, fluorescence was not observed. The incipient degenerate synergid was intensely stained by cationic dyes 24–36 h after anthesis.

Ultrastructure in leaves of Fagus silvatica and Carpinus betulus individuals tolerant and susceptible to SO 2 and heavy metal pollutants

The ultrastructure characteristics of leaves during the development of cell organelles, in the “greening process” of spring, have been studied in pollutant-tolerant and susceptible individuals of beech ( Fagus silvatica) and hornbeam ( Carpinus betulus) in an area polluted with SO 2 (the main pollutant may reach 0.06–2.72 mg/m 3), heavy metals, and other gases discharged by non-iron metal processing factories. Leaves from tolerant beech and hornbeam individuals did not undergo ultrastructural changes compared to control leaves in an unpolluted area. The susceptible and very susceptible individuals of both species gradually undergo modification in organelle ultrastructure not only during the first steps of greening and momentary exposure to air pollution, but also as a result of long-term exposure to chronic pollution in the forest.

Induced Changes in Chloroplast Protein Accumulation during Heat Bleaching in Euglena gracilis

When growing cultures of light-grown Euglena gracilis Z are exposed to slightly elevated temperatures (33 degrees C) there is a time-dependent decrease in chlorophyll (bleaching) and a gradual transformation of chloroplasts into rudimentary plastids. A study was undertaken whose primary objective was to document major changes in polypeptide composition in the stroma and in thylakoids of cells that have been exposed to the bleaching temperature for up to 57 hours. A novel polypeptide of about 60,000 to 63,000 M(r) whose function is presently unknown, accumulates in the stroma and in thylakoids in response to growth at the bleaching temperature. The levels of the large and small subunit of ribuolosebisphosphate carboxylase, on the other hand, decrease to very low levels at about 33 hours and remain very low for the duration of the temperature treatment. Of two polypeptides associated with the light-harvesting chlorophyll-protein complex of photosystem II (28,000 and 24,500 M(r)) only the level of the smaller polypeptide decreases at the elevated temperature. The levels of 28,000 M(r) species remain virtually unchanged throughout the temperature treatment period. Changes in chloroplast polypeptide composition were also studied in cells that were allowed to recover at room temperature from an initial treatment at 33 degrees C. Bleaching Euglena could provide a useful tool for studying the interaction between the nucleus and chloroplast genetic system that govern the development and maintenance of this vital organelle to plants.

Differentiation of leucoplasts: Comparative transition of proplastids to chloroplasts or leucoplasts in trichomes ofStachys lanata leaves

The development of proplastids to chloroplasts or leucoplasts was followed in uniseriate nonglandular hairs, containing chloroplasts, and in glandular hairs, containing leucoplasts, ofStachys lanata leaves. Both hairs grow at the same time from the epidermis. Both chloroplasts and leucoplasts originate from structurally identical proplastids in meristematic cells. At the early stage, ribosomes are absent. After production of the first ribosomes, each plastid population differentiates along its own developmental pathway. In nonglandular hairs, ribosome multiplication occurs within the plastid stroma and a thylakoid system with grana stacks is formed. Ribosomes are attached to membrane vesicles produced by the inner membrane of the plastid envelope, to thylakoids, or are clustered in specialized areas of the stroma. Further development produces typical, small differentiated chloroplasts. In glandular hairs, the production of additional complete ribosomes ceases early. Smaller, transient dense particles are seen within the stroma in the course of the developmental process. The plastids increase in size and there is a transient tubular system but no thylakoids develop. Plastid division proceeds by neck constriction. The latter stage of leucoplast differentiation is characterized by the complete disappearance of ribosomal material and of tubular inner membranes. DNA nucleoids are obvious throughout the developmental period. Unlike chloroplasts, the development of these nonphotosynthetic heterotrophic organelles and the expression of their specialized metabolic activity probably does not involve the synthesis of specific peptides via plastoribosomes.

Septal Structures in Apothecial Tissues of Taxa in the Tribes Scutellinieae and Sowerbyelleae (Pyronemataceae, Pezizales, Ascomycetes)

Septal pore structures are described in asci, ascogenous hyphae, paraphyses, and excipular cells of species of Cheilymenia and Scutellinia (tribe Scutellinieae), and Acervus and Caloscypha (tribe Sowerbyelleae) of the Pyronemataceae. The ascus pore plugs of Cheilymenia and Scutellinia begin as a single electron-opaque band across the pore but develop into banded hemispherical structures within the ascus. Ascus pores of Acervus and Caloscypha are filled with an electron-opaque matrix in young asci, but by maturity they are plugged by a hemispherical, electron opaque structure with membranelike, translucent borders. Pores of the ascogenous hyphae of Cheilymenia and Scutellinia are occluded by Woronin bodies covered by deeply staining amorphous material. Plugging of ascogenous hyphal pores in Acervus and Caloscypha is similar to that of their asci. Lamellate structures are found in the pores of excipular cells in all species studied.Structure and development of septal pore organelles in Acervus and Caloscypha are very similar to those found in members of the tribe Aleurieae but differ significantly from those of the Scutellinieae. Comparisons of pore structures of these two tribes are made with those of the Pezizaceae and Asco-bolaceae. The taxonomic and phylogenetic significance of these data is discussed.

Ultrastructural observations on gastrodermal regeneration in the planarian Dugesia japonica (Turbellaria)

The earliest detectable change during regeneration of the gastrodermis in Dugesia japonica was an aggregation of regenerative cells underneath the gastrodermis remaining at the wound margin. The gastrodermal cells in experimental regenerates retained some of their original characters and presented no indication of cell dedifferentiation. The regenerative cells came into contact with the basal surface of gastrodermal cells, forming stratified cell layers. Differentiation of these cells into gastrodermal cells was initiated by the development of synthetic organelles within their cytoplasm. These differentiating cells gave rise to two different types of gastrodermal cells, namely phagocytic cells and sphere cells. In later stages, there was an apparent movement of differentiated gastrodermal cells towards the parenchyma.

Cytological and ultrastructural changes in the pituitary pars distalis of the goldfish kept in calcium-free environments.

The cytology and ultrastructure of the pars distalis, mainly that of prolactin (PRL) cells, were investigated in goldfish adapted to fresh water (FW) or deionized water (DW) for 20 and 40 days, or gradually adapted to 1/3 artificial sea water (ASW) or 1/3 Ca-free sea water. When compared to PRL cells of goldfish kept in FW, those of goldfish adapted to DW did not show signs of increased activity. The lack of exocytotic activity and the low development of various organelles suggested that cell activity was slightly reduced. In 1/3 ASW, PRL cells were smaller and less active. In 1/3 Ca-free ASW, PRL cells appeared slightly stimulated compared with those of fish in 1/3 ASW. The Golgi area was more developed and a few lamellae of endoplasmic reticulum were observed in some cell islets. However, there was no significant difference between PRL cells of goldfish kept in 1/3 Ca-free ASW and in FW. In 1/3 ASW, which is isosmotic to the blood, thyrotrophs (TSH cells) corticotrophs (ACTH cells) and somatotrophs (STH cells) were not clearly affected. In DW, these cells and their nuclei were significantly enlarged. Their stimulation was also evident in 1/3 Ca-free ASW; values for cellular and nuclear areas were maximal in this environment and significantly higher than those of fish in FW and 1/3 ASW. These data suggest that in addition to the PAS-positive cells of the pars intermedia, highly stimulated in Ca-free environments, other cell types of the pars distalis may be involved in osmoregulation, and that the role of PRL cells is not primordial in the goldfish.

Paracrine control of Leydig cell activity by FSH dependent proteins from sertoli cells: An in vitro study

The regulating effect of follicle-stimulating hormone (FSH) on Leydig cell function was studied using a model of immature porcine Leydig and Sertoli cells cultured in a hormone supplemented defined medium. FSH pretreatment for 2 days of Leydig cells cultured alone was with no effect. FSH pretreatment of Leydig cells cocultured with Sertoli cells increases Leydig cell activity in an FSH dose-dependent manner with a maximal effect observed at 50 ng/ml porcine FSH (pFSH). Leydig cells cultured for 2 days in conditioned medium (CM) by FSH stimulated (FSH-CM) Sertoli cells, as compared to CM by unstimulated (control) (C-CM) Sertoli cells show an increase of their activity with a maximal effect observed at 50 ng/ml pFSH. Leydig cells cultured in CM as compared to non CM, show a marked development of organelles (smooth endoplasmic reticulum and mitochondria) involved in the steroidogenic activity. The activity of FSH-CM as compared to C-CM on Leydig cell function was non dialyzable and trypsin sensitive. These data suggest that Sertoli cells exert a regulatory action on Leydig cell steroidogenic activity via FSH dependent secreted proteins.

Ultrastructural changes in Sertoli cells in ageing humans

Ultrastructural study of seminiferous tubules in ageing men revealed a varying degree of spermatogenetic arrest associated with changes in the Sertoli cells. Approximately half of the Sertoli cells showed a normal mature nuclear appearance although the cytoplasm was altered morphologically. These cells were classified as containing abundant lipid droplets (30%), containing large cytoplasmic vacuoles filled with an amorphous material similar to that in the tubule lumen and surrounded by junctional specializations (8%), multinucleated Sertoli cells (4%), or Sertoli cells with numerous mitochondria displaying tubular cristae (2%). The remaining 7% of Sertoli cells had an immature nuclear appearance and sparse development of the cytoplasmic organelles; these cells probably represent dedifferentiated Sertoli cells. Although individual differences were marked, a correlation between the increase in gonadotrophin levels and changes in both germ cell development and Sertoli cell structure was observed.

Photosynthesis, Morphology, Leaf Anatomy, and Cytogenetics of Hybrids between C3 and C3/C4Panicum Species

The Laxa group of the Panicum genus contains species which have CO(2) exchange and anatomical characteristics intermediate to C(3) and C(4) photosynthetic types (C(3)/C(4)), and also species characterized as C(3). Hybrids were made between two of the C(3)/C(4) species and two C(3) species. Carbon dioxide exchange and morphological, leaf anatomical, and cytogenetic characteristics of F(1) hybrids between Panicum milioides Nees. ex Trin (C(3)/C(4)) and P. laxum Mez. (C(3)), P. spathellosum Doell (C(3)/C(4)) and P. boliviense Hack. (C(3)), and P. spathellosum and P. laxum were studied. There were no consistent differences in apparent photosynthesis, although two of the three hybrids had higher net CO(2) uptake than the C(3) parent. Values of inhibition of apparent photosynthesis by 21% O(2), CO(2) loss in the light, and CO(2) compensation concentration for the hybrids were between those of the parents. All three hybrids showed leaf anatomical traits, especially organelle quantities in the bundle sheath cells, between those of their respective parents. Linear regression of CO(2) compensation concentration on the percentage of mitochondria and chloroplasts in vascular bundle sheaths of the parents and hybrids gave correlation coefficients of -0.94. This suggests that the reduction in CO(2) loss in the C(3)/C(4) species, and to a lesser degree in the F(1) hybrids, was due to development of organelles and perhaps a higher proportion of leaf photorespiration in bundle sheaths. The overall morphology of the hybrids was so different from the parents that they could be described as new taxonomic forms. The chromosomes in the hybrids were mainly unpaired or paired as bivalents indicating possible homology between some parental genomes.

Interaction between benzyladenine and fusicoccin on the development of excised watermelon cotyledons. I. Growth and organelle development

Benzyladenine (BA) stimulates growth and orgenelle development in watermelon cotyledons while fusicoccin (FC) stimulates growth, but has no effect on organelle development. Here, we have examined the effect of BA and FC when administered together to the cotyledon. Cotyledons of watermelon ( Citrullus vulgaris Schrad., cv. Fairfax) were excised from the embryo after 24 h of imbibition and cultured for several days in presence of BA and FC, both 10 −5 M. In some experiments the concentration of BA was varied from 10 −6 to 10 −4 M. In BA + FC the growth rate was higher than in either of the two substances alone. Conversely, all parameters related to organelle development (carotenoid and enzyme levels) were much lower than with BA alone and barely higher than in the water control. Thus FC appears to be a powerful inhibitor of BA-induced organelle development. The inhibition is nearly abolished if the cotyledons are grown in 10 −5 M BA for 2 days before transfer to BA + FC. Enhancement of growth by FC is maximal in the presence of BA concentrations that are not very effective while inhibition of BA-induced carotenoid synthesis is maximal in the presence of BA concentrations that have the highest stimulating effect.

Synthesis of DNA in excised watermelon cotyledons grown in water and benzyladenine

Excised watermelon cotyledons were grown in water and benzyladenine, which greatly promotes growth, breakdown of reserves and development of organelles. In order to investigate the involvement of DNA synthesis in these benzyladenine-induced effects, [(3)H]thymidine was applied continuously (for 3 d) or administered briefly (5 h) to excised cotyledons at various stages of development. Autoradiographic analysis of squashed and sectioned cotyledons showed that both the cytoplasm (mainly in the region of the plastids) and most of the nuclei were labelled. Both types of labelling were promoted by benzyladenine treatment. The highest percentage of labelled nuclei was found in the early stages of growth (first day after excision of cotyledons), long before the burst of enzymatic activities involved in the germination processes. The possible meaning of the increase of nuclear DNA, apart from the normal replicative synthesis preceding cell division, is discussed.

Interaction between benzyladenine and fusicoccin on the development of excised watermelon cotyledons. II. Correlation between growth and proton extrusion

Treatment of excised watermelon ( Citrullus vulgaris Schrad., cv. Fairfax) cotyledons with 10 −5 M fusicoccin (FC) induces stimulation of growth and a marked decrease in pH of the external medium. Treatment of the same cotyledons with 10 −5 M benzyladenine (BA) also stimulates growth, but does not induce a decrease in pH. When BA and FC are administered together the growth rate is higher than with either of the two regulators alone, but the decrease in pH is slightly smaller than with FC alone. The accompanying paper, Fantelli et al., Plant Sci. Lett., 33 (1984) 267, reports that a 2-day preincubation in 10 -5 M BA prevents the inhibitory effect of FC on BA-induced organelle development. We have measured pH changes of the external medium under these experimental conditions. After transfer to FC the pH decreases for 8 h as observed in absence of preincubation with BA, but then increases again, while without preincubation the pH of the medium continues to decrease for an indefinite time. The results suggest that cytokinin-stimulated cotyledon expansion does not involve the continued operation of a proton pump, thus confirming the data obtained by Ross and Rayle, Plant Physiol., 70 (1982) 1470, with cucumber cotyledons. The activation of the pump by FC probably causes an imbalance in ion transport that blocks BA-stimulated organelle development. The preincubation in BA may help to keep the proton pump under control.

Analisi ultrastrutturale degli effetti della monensina in Euglena gracilis, con particolare riguardo all'apparato di Golgi

Abstract Ultrastructural analysis of the effects of monensin in Euglena gracilis, with special reference to the Golgi apparatus. - The monovalent ionophore, monensin, is known to affect the mature (trans) half of the dictyosomes of several organisms, including Euglena gracilis. We demonstrated that the exposure to high concentrations of this compound (2.5 × 10−5 to 10−4M) provoked remarkable swelling also in the forming (cis) half of Euglena cisternae. Additional dilations affected the thylakoids of both mature chloroplasts and proplastids of greening cells in which the organelle development was slower than in the control group. No osmotic swelling was observed for the mitochondria. Since monnesin exchanges one proton for each monovalent cation (Na+ or K+) transported, it follows that an energy driven influx of H+ is necessary to accumulate sufficient osmotically active ions in a membrane compartment. Thus it is possible that H+-ATPases are present on both forming and mature half of Euglena dictyosomes.

Cytophysiological correlations between prothoracic gland activity and hemolymph ecdysteroid concentrations in Rhodnius prolixus during the fifth larval instar: Further studies in normal and decapitated larvae

Hemolymph ecdysteroid titers in fifth instar larvae of Rhodnius prolixus were determined by radioimmunoassay, and their prothoracic glands were excised and examined by electron microscopy. During the last larval instar, the titer of ecdysteroid increased between the head-critical period until Day 13, at which time the peak titer was 3100 pg 20-hydroxyecdysone equivalents/μl. The activation of secretory cells at the time of the second period of prothoracicotropic hormone release was correlated with the development of major cellular organelles. The smooth endoplasmic reticulum first appeared at the head-critical period and the proliferated in close relation to the increase in ecdysteroid titer until Day 13, after which time it disappeared. Mitochondria expand and develop tubular cristae. They are closely associated with the smooth endoplasmic reticulum. When insects were decapitated, hemolymph ecdysteroid titer remained below 10 pg/μl and the prothoracic gland cells failed to develop smooth endoplasmic reticulum. We conclude that in the prothoracic gland cells as well as other steroidogenic tissues the smooth endoplasmic reticulum in association with mitochondria is involved in ecdysone biosynthesis.

Lysosomes and removal of the basal lamina of ameloblasts in early stages of odontogenesis

Differentiation of ameloblasts is characterised by the development of cytoplasmic organelles and changes in the distal cytoplasm and surface adjacent to the basal lamina. Examination of rat tooth germs prepared for thin section electron microscopy and for freeze fracture, and also stained for acid phosphatase, reveals that three concomitant events occur in this region. The distal surface membrane becomes progressively more undulated, there is an increase in acid phosphatase-containing membrane-bound vesicles (lysosomes) and the basal lamina becomes less apparent and finally disappears. Since the progressive disappearance of the basal lamina is accompanied by an increase in lysosomes, it is possible that lysosomal enzymes are involved in the breakdown of the basal lamina or, alternatively, that the basal lamina is broken down by enzymes derived from odontoblasts, and that its remnants are taken up by the many coated pits and invaginations of the distal surface membrane to be further degraded in the lysosomal system.

Subcellular compartments and protein topogenesis.

A cell is surrounded by a plasma membrane. It contains various organelles, most of which are enclosed by limiting membranes. The intracellular space is thus divided into a number of subcellular compartments. Structurally, a cell is composed of membranes and the spaces enclosed by those membranes. In order to classify these compartments, the extracellular space has been designated S1 and whenever a unit membrane structure is crossed to arrive at the next space, one is added to term; the cytoplasmic space becomes S2, the intraluminal space of the endoplasmic reticulum and the intermembrane space of the mitochondria S3, and the matrix space of the mitochondria S4. Similarly, the plasma membrane is M1, the outer membrane of the mitochondria M2, and the inner counterpart M3. This classification of the subcellular compartments is useful in understanding a number of complicated cellular structures and functions. The intracellular transport of newly synthesized protein (protein topogenesis) and the probable development of subcellular organelles during phylogenesis of eukaryotic cells is discussed in terms of these subcellular compartments.

Quantitative analyses of neuronal development in the lateral motor column of mouse spinal cord. II. Development of motor neuronal organelles.

The development of organelles within presumptive alpha motor neuronal somata was studied by electron microscopic morphometric analysis. Cells with large nuclei were selected for sampling from the lateral motor column of the brachial spinal cord of mouse embryos ranging in age from embryonic day 11 (E11) through E16. The first objective was to compare the cytodifferentiation of alpha motor neuronal somata among three genetically different strains of mice that differ in the development of forelimb reflex behavior and associated pathway synaptogenesis (Vaughn et al., '75). On the basis of multiple linear regression analyses, no significant differences were found among strains for either the initial levels or rates of cytodifferentiation. As a result, the data were combined for all three strains to analyze organelle changes during early neuronal development. The average areas of perikaryal cytoplasm and nuclei increased significantly. In addition, the relative areas of nucleoli, mitochondria, Golgi complexes, and rough endoplasmic reticulum increased, while the relative areas of heterochromatin and "free" ribosomes decreased. There were significant increases in the number of mitochondria and Golgi complexes per unit area of perikaryal cytoplasm. The average size of mitochondria appeared to increase during development, but was significantly smaller in adult alpha motor neurons than in embryonic specimens. In contrast, the average size of individual Golgi complexes was relatively constant throughout embryonic development, as well as in the adult. In general, the cytodifferentiation of alpha motor neurons appeared to progress in a relatively constant, linear fashion between E11 and E16.

Study on the influence of NA-872 (ambroxol) and dexamethasone on the differentiation of Clara cells in albino mice.

The techniques of light and electron microscopy were used to study the sequence of changes in the fine structure of the developing nonciliated bronchiolar cells in the last quarter of gestation in the mouse, and up to the 3rd postnatal day. Control animals were compared with two groups that received either dexamethasone or ambroxol. At the beginning of the study no identifiable Clara cells were seen in any group, and phenotypically differentiated cells were seen until 1 day post partum in every group examined. Dexamethasone appears to increase the glycogen deposition found in the cells, reaching its maximum 1 day prior to delivery. Ambroxol induced an earlier development of the secretory organelles, beginning on day 17 of gestation. In the differentiated cells more secretory dense granules were found in this group; and at the 3rd day post partum a great accumulation of secretory product that filled large areas of cytoplasm was seen only in the ambroxol-treated group. The significance of these finding is discussed.

CELLULAR ORGANELLES AND CELL‐WALL FORMATION IN FIBRES FROM THE FLOWERING STEM OF LOLIUM TEMULENTUM L.

SummaryThe structure of the thick wall of lignified fibre cells from the flowering stem of Lolium temulentum L. is described. The formation of wall layers is related to the period of cell elongation and to the presence or absence and state of development of organelles which are possibly involved in the formation of the cell wall.It is suggested that while the fibre cells are still elongating, rough endoplasmic reticulum (RER) and dictyosomes associated with small, electron transparent vesicles are involved in the formation of the cell wall, whereas in fibre cells which are nearing the end of elongation, and those which have stopped elongating, it is suggested that microtubules, lomasomes and dictyosomes associated with large electron transparent vesicles and small vesicles with electron dense cores are involved.The nomenclature for labelling wall layers as primary or secondary is discussed.