Corn Mitochondrial Swelling and Contraction-an Alternate Interpretation

Mitochondria isolated from 3-day-old etiolated corn shoots (Zea mays L.) can be categorized into three separate groups, each group characteristic of the cell type from which the mitochondria were isolated. Phloem sieve tubes and some adjacent parenchyma cells contain mitochondria that have few cristae and little amorphous matrix. Mitochondria from meristematic and undifferentiated cells have more cristae and matrix. Vaculate and differentiated cells have mitochondria with well-developed cristae and abundant matrix. Each mitochondrial type exhibits typical in vitro spontaneous swelling and substrate-induced contraction responses. characterized by change or lack of change in cristae size and in density of amorphous material. For the second and third types of mitochondria, swelling and contraction are characterized by a change in degree of cristae size and in matrix density. The first type undergoes few changes upon swelling or contraction. Radical changes of the inner membrane, withdrawal and infolding, are associated with cell differentiation and not with swelling and contraction of isolated corn shoot mitochondria.     

Isolation and properties of cholesterol esterstorage granules from ovarian tissues

Cholesterol ester-storage granules were isolated from luteinized rat ovary and rabbit ovarian interstitial tissue by centrifugal flotation and were investigated with regard to their structure and function. Cholesterol ester, protein, phospholipid and unesterified cholesterol accounted for the dry weight of granules from luteinized rat ovary. The protein and the phospholipid were resistant to removal by washing. Substrate specificities of nucleotide phosphatase and specific radioactivities of lipid-soluble P (determined after administration of [³²P]P_i in vivo) were the same in granules and in a microsomal fraction from the same tissue. After administration of [³²P]P_i in vivo, luteinizing hormone increased the specific radioactivity of lipid-soluble P in granules, mitochondria and the microsomal fraction. Since granules did not swell in hypo-osmotic media, whereas microsomal particles did, it is suggested that adherent phospholipid and protein in granule suspensions is unlikely to result from contamination with endoplasmic reticulum. Luteinizing hormone administered in vivo increased the phospholipid and unesterified cholesterol contents of isolated granules relative to their cholesterol ester content, and also tended to raise their protein content. This treatment decreased the ability of isolated granules to act as a substrate for cholesterol esterase in vitro and increased the activity of cholesterol esterase. Cycloheximide in vivo also raised the unesterified cholesterol/cholesterol ester ratio of isolated granules, and when administered with luteinizing hormone acted synergistically to bring about a further increase. These results are considered compatible with evidence obtained by microscopy which suggests that granules may be surrounded by a membrane, that they arise by pinching off from the endoplasmic reticulum, and that they shrink on trophic stimulation of the tissue.     

Structural studies of the adrenal zona glomerulosa and renal juxtaglomerular apparatus in pregnant sheep

The ultrastructural changes in the adrenal zona glomerulosa and renal juxtaglomerular apparatus have been examined during normal pregnancy in sheep. As pregnancy progressed, increasing numbers of cells in the adrenal zona glomerulosa displayed mitochondria with straight tubular "rod-like" structures replacing their normal lamelliform cristae; groups of cells showing these mitochondrial changes were predominantly located in the middle and superficial regions of the zona glomerulosa, but at all stages remained interspersed with cells with apparently normal mitochondria. In the same animals, the renal juxtaglomerular index was raised, reflecting an increase in renin storage, and juxtaglomerular myoepithelioid cells showed increased numbers of cytoplasmic granules, but no apparent increase in granular endoplasmic reticulum and Golgi profiles; there were no distinguishing morphological changes in juxtaglomerular peripolar cells. These findings provide morphologic evidence of stimulation of the adrenal zona glomerulosa in association with increased juxtaglomerular renin storage during pregnancy. The mitochondrial changes observed in an increasing proportion of cells in the zona glomerulosa closely resemble those seen in sodium-depleted animals, and may reflect the altered steroidogenic capacity of the adrenal gland in pregnant sheep. The finding of groups of cells displaying altered mitochondria lying next to cells with normal mitochondria suggests the presence of cells with different sensitivities to stimuli for aldosterone production or may indicate the presence of different cell types in the zona glomerulosa responding to different stimuli.     

MITOCHONDRIAL BIOGENESIS DURING DIFFERENTIATION OF ARTEMIA SALINA CYSTS

Mitochondria isolated from cysts of Artemia salina (brine shrimp) were found to be devoid of cristae and to possess a low respiratory capability. Hydration of the cysts induces marked biochemical and morphological changes in the mitochondria. Their biogenesis proceeds in two stages. The first stage is completed within 1 h and is characterized by a rapid increase in the respiratory capability of the mitochondria, their cytochrome oxidase, cytochrome b, cytochrome c and perhaps some morphological changes. In the second stage there is an increase in the protein-synthesizing capacity of the mitochondria as well as striking changes in mitochondrial morphology leading to the formation of cristae.     

The effect of heating on the respiration of MC7 and D23 tumour tissue

The sensitivity of the tissue respiration of two tumours and liver slices to heat has been studied. The tumour tissue is sensitive to in vitro preincubation at temperatures above 43°C, whereas liver slices were less temperature sensitive. The inclusion of 1 mM tetracaine during preincubation sensitizes the tumour tissue to heating. In vivo heating of the tumour tissue at 44°C for 1h was not inhibitory of respiration when subsequently measured at 37°C. Mitochondria isolated from the D23 hepatoma tissue showed coupled respiration, however mitochondria isolated from in vivo heated tumour did not show coupled respiration. It contrast to mitochondria isolated from unheated tissue, these mitochondria lacked cristae and contained electron-dense granules, indicators of damage. The lack of effect of an in vivo heat-dose, known to cause tumour regression, on respiration and the reports that ATP levels are unaffected by such heating, suggests that cell respiration is not a primary lesion in cellular heat injury. This implies that the observed impairment of mitochondrial function following in vivo heating is best explained if the heating sensitized the mitochondria to subsequent damage during isolation.     

泥螺卵黄发生过程中线粒体的变化

利用透射电镜（TEM）技术研究了泥螺卵黄发生过程中线粒体的形态结构的变化特点,结果表明,从卵黄发生早期到晚期,卵母细胞内线粒体经历了从外部形态到内部结构的一系列变化。卵黄合成初期的卵母细胞内,线粒体多,结构典型,仅部分线粒体外膜破裂,嵴 和内膜逐渐消失,卵黄发生中期,线粒体基质空泡化,嵴和内膜消失,腔内充满颗粒状物质,最后演变成卵黄颗粒,随着卵母细胞的发育,卵黄颗粒的数量和直径逐渐增加,卵黄发生后期,卵质中胞器不发达,细胞质中充满卵黄颗粒,在卵黄颗粒之间仅有少量线粒体存在,提供细胞代谢所需的能量,此外,对线粒体在卵黄形成中的功能,去向及行为变化等 进行了讨论。     

Fine structure of the parotid gland in the crest-tailed marsupial-rat (Dasyuroides byrnei).

The parotid gland of Dasyuroides byrnei was examined by light microscopy, and transmission and scanning electron microscopy. The acini were composed predominantly of seromucous cells with a few mucous cells. The seromucous cells were light or dark cells containing acidophilic spherical granules of moderate to high electron density and had well-developed cytoplasmic organelles-ordinary mitochondria and large mitochondria with tubular cristae, RER with vesicular or tubular elements, and Golgi apparatus with lamellae, vesicles and vacuoles. The mucous cells had basophilic amorphous granules of low electron density, like those of ordinary mucous cells. The intercalated ducts were composed of simple cuboidal light cells having a few electron-dense granules. The striated ducts consisted of tall columnar light cells containing numerous vesicles and mitochondria with tubular cristae, the same as found in acinar seromucous cells.     

Structural changes occurring in interrenal tissue of the duck (Anas platyrhynchos) following adenohypophysectomy and treatment in vivo and in vitro with corticotropin

Adrenal glands from ACTH-treated intact ducks and chronically adenohypophysectomized ducks showed clear zonation into a subcapsular zone (SCZ) and an inner zone (IZ). Adenohypophysectomy caused ultrastructural changes in the IZ but not in the SCZ cells. These included increases in lipid droplets, changes in mitochondrial cristae from tubular to shelf-like, and changes in the shape of the nuclei from spherical to crenated. These changes were reversed by treatment with ACTH. Also, cells of the IZ, but not the SCZ, of adrenals from intact birds given ACTH showed more SER, more dense bodies, fewer lipid droplets and more prominent Golgi complexes. IZ cells incubated in buffer containing no ACTH developed mitochondria with shelf-like cristae and numerous opaque granules in the matrix. Exposure to buffer containing ACTH caused the mitochondrial cristae to become tubular and the matrix granules either decreased in number or disappeared. The granules could be extracted by incubating sections with chelating agents. The mitochondria in SCZ cells did not respond structurally to the presence of ACTH in the incubation medium but the matrix granules, like those in IZ cells, responded to the presence of chelating agents.     

Fasciola hepatica: Stereological analysis of vitelline cell development

Cytomorphosis of vitelline cells in Fasciola hepatica has been studied quantitatively by means of a Kontron Videoplan computerized image analyser. The process of vitelline cell development was subdivided into four characteristic phases: the stem cell, the intermediate type 1 cell, the intermediate type 2 cell, and the mature cell. The whole cell and the following constituent organelles, the nucleus, nucleolus, mitochondria, granular endoplasmic reticulum (GER), secretory granules, glycogen, heterophagosomes, and lipid, were analysed at each phase. Results indicated that there was a significant increase in nuclear size between the two intermediate cell stages, and a significant increase in nucleolar size between the stem cell and intermediate type 1 cell; the changes were related to possible gene activation, ribosome production, and cell synthesis required for both cell growth and secretory production. Mitochondria increased in number and showed changes in volume and surface area of whole organelles and their cristae such that these correlated with the energy demands of growth and synthesis. The GER increased its average total volume some 16 times and its average total surface area some 25 times between the stem cell and mature cell stages. Even this increase masked the true extent of membrane production by this system, since membrane was transferred to secretory granules; in reality the GER or GER-derived membranes increased more than 42 times between the stem cell and mature cell stages. Shell globules and glycogen eventually contributed 21 and 20%, respectively, to cytoplasmic volume, while heterophagosomes contributed 14% and lipid only 3%. Residual cytoplasm was shown to be an important component in cytomorphosis, comprising never less than 40% of the total cytoplasmic volume and it was shown to increase prior to or parallel with the development and expansion of other systems.     

Mitochondria Isolated from Rat Brown Adipose Tissue and Liver

Mitochondrial fractions, relatively free from contamination by other cytoplasmic structures, have been isolated by differential centrifugation from homogenates of brown adipose tissue from starved rats. It was possible in such fractions to distinguish two types of mitochondria in this tissue. Type I mitochondria, when morphologically intact, are limited by a bilaminar membrane and show regular parallel cristae. In isolated fractions, a proportion of these mitochondria are swollen, vacuolation occurring within the cristae between their limiting membranes. Type II mitochondria are distinguished from the more numerous type I bodies by the opaque appearance of their matrix. They are limited by a membrane which is in part single, and in part double. They show a few, but crisply outlined internal membranes. Vacuolation of this type of mitochondrion has not been observed. Vacuolation comparable to that in brown fat mitochondria was also observed between the two laminae of the enclosing membrane and within the cristae of liver mitochondria.     

A study of oogenesis and early embryogenesis in the rabbit, Oryctolagus cuniculus, with special reference to the structural changes of mitochondria

The structural changes of mitochondria that occur during oogenesis and early embryogenesis in the rabbit have been examined with the electron microscope. Mitochondria of oogonia are both elongate and oval and contain a variable number of cristae which may or may not traverse the longitudinal axis of the organelle. When oogonia differentiate into oocytes, mitochondria become spheroidal and their cristae are sparse when compared with those found in the ellipsoidal organelles of concomitantly maturing follicle cells. As differentiation proceeds, the cristae of the mitochondria display varied configurations. For example, many display an arch-like arrangement in several regions of the organelle whereas others contain a pair of concentric membranes closely associated with limiting membrane of the mitochondrion. Mitochondria of stages from the fertilized egg to the morula possess the same internal structure as those of young oocytes. As the morula differentiates into a blastocyst there is a gradual increase in the size of the mitochondria and an increase in the number of cristae. We believe that the number and modifications of cristae indicate stages of mitochondriogenesis and the level of enzymatic activity in which this organelle is engaged during oogenesis and early embryogenesis.     

Three-Dimensional Reconstruction,by TEM Tomography,of the Ultrastructural Modifications Occurring in Cucumis sativus L. Mitochondria under Fe Deficiency

Background

Mitochondria, as recently suggested, might be involved in iron sensing and signalling pathways in plant cells. For a better understanding of the role of these organelles in mediating the Fe deficiency responses in plant cells, it is crucial to provide a full overview of their modifications occurring under Fe-limited conditions. The aim of this work is to characterize the ultrastructural as well as the biochemical changes occurring in leaf mitochondria of cucumber (Cucumis sativus L.) plants grown under Fe deficiency.

Methodology/Results

Mitochondrial ultrastructure was investigated by transmission electron microscopy (TEM) and electron tomography techniques, which allowed a three-dimensional (3D) reconstruction of cellular structures. These analyses reveal that mitochondria isolated from cucumber leaves appear in the cristae junction model conformation and that Fe deficiency strongly alters both the number and the volume of cristae. The ultrastructural changes observed in mitochondria isolated from Fe-deficient leaves reflect a metabolic status characterized by a respiratory chain operating at a lower rate (orthodox-like conformation) with respect to mitochondria from control leaves.

Conclusions

To our knowledge, this is the first report showing a 3D reconstruction of plant mitochondria. Furthermore, these results suggest that a detailed characterization of the link between changes in the ultrastructure and functionality of mitochondria during different nutritional conditions, can provide a successful approach to understand the role of these organelles in the plant response to Fe deficiency.     

Electron microscopy of the adrenal medulla of the newborn dog under hypothermia and asphyxia.

The left adrenal medullas of 20 (5 litters of 4) day-old dogs were studied with the electron microscope. The right adrenal medullas of the same animals had been examined by fluorescence microscopy and the results reported previously. In each litter one animal served as a coenothermic (37 degrees C) and one a hypothermic control (15 degrees C). The third animal (at 37 degrees C) was asphyxiated until twice its time of last gasp (about 32 min) and the fourth was cooled to 15 degrees C and asphyxiated for the same length of time as the third animal. The induction of hypothermia (to 15 degrees C) in unanesthetized puppies results in a decrease (32%) in dense-cored granules, an enlargement of mitochondria, and slight dilation of the endoplasmic reticulum. In coenothermic puppies asphyxiation to twice the time of last gasp is accompanied by the following changes: loss of dense-cored granules (52%); swelling of nuclei; clumping and marginal aggregation of nuclear chromatin material; dilation of the endoplasmic reticulum; swelling, loss of cristae and rarefaction of the matrices of mitochondria. The changes in some cells were greater than others. Many of these changes are considered to demonstrate anoxic damage. Under the conditions of the present experiments, hypothermia protected most of the adrenal medullary cells from anoxic damage.     

Incorporation of tritiated thymidine into mitochondrial DNA of the liver and kidney cells of chickens and mice in tissue culture

Summary ³H-thymidine incorporation into mitochondrial DNA of the liver and the kidney cells of chick embryos and newborn mice in tissue culture was shown by means of electron microscope radioautography with accurate localization. In these cells, about 20% of all the mitochondria were labeled at their matrices between the cristae within 4 hours in contact with the radioisotope, which were removed by DN'ase.From the results, it is clear that the mitochondria of avian and mammalian cells in tissue culture synthesize DNA.     

SOME OBSERVATIONS ON THE FINE STRUCTURE OF THE LUTEIN CELLS OF X-IRRADIATED RAT OVARY

The ovaries of 10- to 13-week-old rats were exteriorized and irradiated with sterilizing doses of X-rays. Following treatment, the animals entered a phase of constant vaginal cornification. Animals were killed 8 to 12 wk after the onset of this phase, and their ovaries were prepared for electron microscopy. Tissue was fixed in glutaraldehyde, postfixed in osmium tetroxide (Millonig's, phosphate-buffered), and embedded in Epon. Lutein cells from these ovaries were compared with those from sham-irradiated controls. The cytoplasm of lutein cells from experimental animals was characterized by an increase in the amount of agranular endoplasmic reticulum and by an increase in the number of mitochondria. These mitochondria are more variable in external form and often possess increased numbers of villiform cristae. Other features noted were a decrease in the amount of cytoplasmic lipid granules and an increase in cell size and surface irregularity. The significance of the morphological findings is discussed in relation to ovarian hormone production in animals sterilized by X-irradiation.     

Ultrastructural studies of oocytes and embryos derived from females flies carrying the grandchildless mutation in Drosophila subobscura

The maternal effect mutant grandchildless in Drosophila subobscura has been analyzed with the electron microscope. The original mutation was linked to a visible genetic marker and established in a balanced stock. Oocytes and early embryos were examined by both transmission and scanning electron microscopy. The earliest defect is seen in mutant eggs and occurs at the end of oogenesis. In the cortex, at both the anterior and the posterior tips, regions appear which are free of ribosomes, mitochondria, and other cytoplasmic organelles. Most of the polar granules are included in these regions at the posterior tip. Following oviposition, this cytoplasmic segregation is no longer observed and most polar granules have disappeared. The few remaining granules are presumed to derive from the peripheral polar plasm which does not become segregated. During embryogenesis there is a retarded movement of nuclei to the anterior and posterior cortices. At the posterior tip nuclei are delayed in reaching the lateral sides and never move directly into the posterior polar plasm. Pole cells never form. After the last syncytial division the lateral nuclei move under the posterior polar plasm to complete the blastoderm. The posterior polar plasm itself protrudes during blastoderm formation as long cytoplasmic extensions which separate from the blastoderm as cytoplasmic blebs. Neither polar granules nor mitochondria are found in these blebs. The grandchildless phenotype is due to the failure of nuclei to migrate directly into the posterior polar plasm. The defect in the polar plasm presumably is related to the process in mature eggs whereby portions of the cortex become segregated at both anterior and posterior tips. This process may change the properties of the posterior polar plasm so that nuclei do not penetrate into it.     

Fine structure of spermatogonia and intercellular bridges in Macaca nemestrina

Spermatogonia of the monkey, Macaca nemestrina, were studied with the electron microscope. The spermatogonial nucleus is characterized by dense homogeneous chromatin and an eccentric nucleolus with a prominent surrounding clear zone. Cytoplasm consists chiefly of free ribosomes and vesicular endoplasmic reticulum. Scattered mitochondria with closely spaced transverse cristae are arranged singly and in pairs separated by thin electron-dense bands. Binucleated spermatogonia resemble other spermatogonia in their ultrastructural characteristics, but contain an increased number of lysosome-like structures and degenerating mitochondria. Spermatogonial interconnections are of two types: broad cytoplasmic connections and narrow intercellular bridges. Connected cells are always identical in appearance and stage of maturation. Multiple connections occur. Interconnection of spermatogonia provides a syncytial type of arrangement which allows synchronization of differentiation and results in similar apperance of adjoining cells. Similarity of regressive changes in adjacent degenerating cells is explained by the presence of intercellular bridges.     

Paragonimus westermani possesses aerobic and anaerobic mitochondria in different tissues,adapting to fluctuating oxygen tension in microaerobic habitats

We previously showed that adult Paragonimus westermani, the causative agent of paragonimiasis and whose habitat is the host lung, possesses both aerobic and anaerobic respiratory chains, i.e., cyanide-sensitive succinate oxidase and NADH-fumarate reductase systems, in isolated mitochondria (Takamiya et al., 1994). This finding raises the intriguing question as to whether adult Paragonimus worms possess two different populations of mitochondria, one having an aerobic succinate oxidase system and the other an anaerobic fumarate reductase system, or whether the worms possess a single population of mitochondria possessing both respiratory chains (i.e., mixed-functional mitochondria). Staining of trematode tissues for cytochrome c oxidase activity showed three types of mitochondrial populations: small, strongly stained mitochondria with many cristae, localised in the tegument and tegumental cells; and two larger parenchymal cell mitochondria, one with developed cristae and the other with few cristae. The tegumental and parenchymal mitochondria could be separated by isopycnic density-gradient centrifugation and showed different morphological characteristics and respiratory activities, with low-density tegumental mitochondria having cytochrome c oxidase activity and high-density parenchymal mitochondria having fumarate reductase activity. These results indicate that Paragonimus worms possess three different populations of mitochondria, which are distributed throughout trematode tissues and function facultatively, rather than having mixed-functional mitochondria.     

Fine structure of the merozoites of Barroussia schneideri parasitic in Lithobius forficatus

The ultrastructure of the merozoites of the parasite Barroussia schneiden (Bütschli, 1882) Reichenow & Schellack, 1912 in the intestinal cells of its centipede host, Lithobius forficatus (L) is described. The pellicle consists of a single outer and a double inner membrane under which there are 51 microtubules extending longitudinally. A micropore is present. The characteristic organelles and cytoplasmic inclusions of the merozoites of the Eimeriidac arc present: conoid, rhoptries (possibly 6), micronemes, nucleus with nueleolus, mitochondria with bulbous cristae, prominent Golgi complex, polysaccharide granules and granular endoplasmic reticulum.     

Histological, histochemical and ultrastructural studies on the interrenal and chromaffin cells of the fathead minnow, Pimephales promelas Rafmesque

Light and electron microscopic examination of fathead minnow head kidneys revealed that the interrenal and chromaffin cells were intermingled and always closely associated with the cardinal veins and their tributaries. Histochemical tests for lipids in the interrenal cells were positive, and two types of chromaffin cells were indicated by chromaffin reactions. Interrenal cells contained abundant smooth endoplasmic reticulum and mitochondria with tubulo-vesicular cristae, characteristic of steroid-producing cells. Only one interrenal cell type was found. Two types of chromaffin cells were present with differences in cytoplasmic density and in types of granules. In light cells, adrenaline granules were most common, and in dark cells noradrenaline granules predominated.