The ultrastructural development of plastids in leaves of maize plants exposed to continuous illumination

Summary Chloroplast differentiation in relation to increasing leaf age has been investigated in maize plants exposed to continuous illumination. In the young leaves the proplastids differentiate into chloroplasts containing well organized grana as well as prolamellar bodies. In the older leaves, while plastids differentiate, the prolamellar bodies are no longer detectable. Chloroplast ability to build up prolamellar bodies does not seems so much a light dependent process as it is affected by cell differentiation rate.Supported by a grant of C.N.R.     

Ultrastructural evidence for inhibition of chitin synthesis by nikkomycin

Summary The nucleoside antibiotic nikkomycin has proved to be an effective inhibitor of chitin synthesis in the Mexican bean beetleEpilachna varivestis. Ultrastructural investigations show defects in the procuticular area after nikkomycin application which suggest the complete absence of chitin. A cuticle like this is inflexible and too brittle to satisfy its normal function as an exoskeleton. The individuals are not able to free themselves from the exuvia and finally die. Therefore nikkomycin seems to be a potential insecticide with high specifity.     

Ultrastructural localization of mercury in adrenals from rats exposed to methyl mercury

Accumulations of mercury have been demonstrated in adrenal glands by light and electron microscopy with a highly sensitive histochemical technique. Rats were exposed to methyl mercury in drinking water (20 mg/l) for 7-180 days, or were given intraperitoneal injections of methyl mercury (daily dose 100 or 200 micrograms). The amount and location of the mercury deposits were dependent upon the exposure time, the method of administration and the amount administered. In rats exposed to methyl mercury in drinking water, accumulations were often observed in both the zona glomerulosa and reticularis. They appeared first in the zona glomerulosa of animals treated for 1 week. In the zona fasciculata, deposits were observed only in the animals treated for 50 to 180 days. In animals treated for 180 days the cytoplasm of the cells in the zona fasciculata was heavily vacuolated and distinct necrotic cells were observed in other cortical zones. In the chromaffin cells, a slight increase in the amount of deposits was observed with increasing exposure time. Both epinephrenic and norepinephrenic cells contained deposits. Only a few deposits were observed in the cortical and chromaffin cells of animals treated with intraperitoneal injections. Ultrastructural deposits were observed in the lysosomes of cortical cells and in both lysosomes and secretory granules of chromaffin cells.     

Morphologic changes in the pineal gland of rats exposed to continuous darkness

We examined the pineal structure of rats exposed to constant darkness (DD) at light microscopic level. Two groups of rats were exposed to 12:12 light/dark cycle (LD) or DD from their prenatal ontogenesis and then for 3 months after birth. The gland structure of DD rats was observed to have an active appearance. Some of the observed pinealocytes with light nuclei from DD rats were determined to contain double nucleoli. Nuclear area and perimeter of both dark and light types were greater in rats kept in DD than in LD. Rats exposed to DD had more cells with light nuclei and lesser cells with dark ones than rats kept in LD. No significant differences in nuclear characteristics of intermediate type were found between rats kept in LD and those kept in DD. The activity of mammalian pineal can be altered by light conditions to which the animal is exposed.     

Ultrastructural characteristics of aortic endothelial cells in borderline hypertensive rats exposed to chronic social stress

Genetic predisposition and social stress may represent important risk factors in etiology of hypertension associated with endothelial dysfunction. Perturbations of endothelial structural integrity are also critical for the pathogenesis of vascular diseases. We examined effect of chronic social stress on structure of aortic endothelium in borderline hypertensive (BHR) and normotensive Wistar rats. Male BHR - offspring of Wistar mothers and SHR fathers and age-matched W were exposed to 6-week crowding stress (5 rats/cage, 200 cm2/rat). Aortic tissue was processed for electron microscopy and NO synthase activity measurement. Crowding stress significantly increased blood pressure in BHR compared to basal values (140+/-3 mm Hg vs. 130+/-3 mm Hg, p<0.05) and reduced enzyme activity by 37 % (p<0.01) in the aorta of BHR. Local slight structural alterations of endothelium were found in non-stressed BHR (p<0.001) when compared with Wistar rats. Chronic stress caused marked (p<0.005) subcellular injury of endothelial cells in aorta of BHR characterized by mitochondrial damage, presence of vacuoles, increased number of lysosomes, Weibel-Palade bodies, changes of intercellular connections and local disruption of endothelium, while only slight changes were seen in Wistar rats. Results suggest increased sensitivity of aortic endothelium of BHR to chronic crowding that may contribute to acceleration of arterial dysfunction.     

Chloroplast fine structure in the japonica-2 maize mutant exposed to continuous illumination. 2. The white tissues.

Exposure to continuous illumination causes an enhancement of thylakoid swelling in the mesophyll chloroplasts of the white tissues of the japonica-2 maize mutant. In the bundle sheath plastids the effects of continuous illumination are striking and intriguing, because a regular honeycomb-like fret of membranes is formed from a provesicular body. No interpretation of this fret of membranes is, at present, possible.     

Chloroplast fine structure in the japonica-2 maize mutant exposed to continuous illumination. 1. The green tissues.

Exposure to continuous illumination causes the appearance of numerous plastoglobuli in the stroma of both the mesophyll and bundle sheath chloroplasts of the green tissues of the leaves of the japonica-2 mutant of maize. In the pale green tissues the thylakoids have markedly swollen membranes. Another feature of the plastids exposed to continuous illumination is the heavy accumulation of starch. The japonica-2 chloroplasts show a different sensitivity to light, the chloroplasts of the pale green tissues being affected more markedly than the ones of the dark green tissues, and the bundle sheath chloroplasts more than those of the mesophyll. The effects of continuous illumination may be interpreted as an acceleration of chloroplast ontogenesis.     

Dopamine antagonist speeds up tail regeneration in lizards exposed to continuous darkness: evidence for prolactin involvement

In earlier studies, we demonstrated that continuous light (LL:LD, 24:0) stimulated tail regeneration whereas continuous darkness (DD:LD, 0:24) and pinealectomy depressed the same in the Gekkonid lizard, Hemidactylus flaviviridis, and, furthermore, exogenous prolactin significantly enhanced the regeneration process in lizards kept in 0:24 LD. However, the regeneration process in animals exposed to 24:0 LD was unaffected by the dopamine agonist, bromocriptine. This study with pimozide, an antipsychotic drug, and a potent dopamine receptor antagonist was conducted to ascertain whether the dopaminergic regulation of prolactin release is operative in lizards, as in mammals, and to provide further evidence for prolactin involvement in regenerative growth. Once daily intraperitoneal injection of 50 micrograms/kg pimozide to H. flaviviridis, 5 days prior to tail autotomy and 50 days thereafter, stimulated the regeneration process in lizards exposed to 0:24 LD. The initiation of regeneration, the total length of new growth (regenerate) produced by Day 50, and the total percentage replacement of the lost (autotomized) tails at the end of 50 days of experimentation were all significantly enhanced in pimozide-treated animals as compared with their counterparts injected with 0.6% sterile saline; in fact, better than saline-injected controls exposed to 24:0 LD of 638 lux intensity. The daily growth rate was also enhanced in pimozide-treated lizards. Interestingly, the pattern of regeneration as well as the final regenerate of pimozide-treated lizards were similar to those observed earlier in ovine prolactin-treated animals exposed to similar experimental photoperiodic schedules.(ABSTRACT TRUNCATED AT 250 WORDS)     

Ultrastructural aspects of the earwig ovary

Ultrastructural studies of the pre-vitellogenic ovaries of Euborellia annulipes indicate an overall structure basically similar to that of other insect ovaries. The membrane surrounding the pore connecting the nurse cell and oöcyte is coated with a thick electron dense material, whereas the cytoplasmic bridge contains few microtubules. All evidence indicates a unidirectional flow of materials synthesized or assembled in the nurse cell into the developing oöcyte.     

Influence of long-term continuous illumination on the nuclear volume of hypothalamic neurons in female rats

A light microscopic quantitative analysis was performed for studying the effects of long-term exposure to continuous illumination on hypothalamic morphology in female rats. Nuclear volumes of neurons in the suprachiasmatic nucleus, paraventricular nucleus, ventromedial nucleus and preoptic area were measured in 16-18 month-old Long-Evans female rats which had been exposed to continuous light for 11 months. Significant nuclear volume shrinkage could be observed in all investigated regions except for the preoptic area in these animals when compared to that of control rats kept under a photoperiod of 14h light and 10h dark. The relationship between morphological changes of hypothalamic neurons and the marked alteration of melatonin and estrogen levels induced by long-term exposure to continuous light is discussed.     

Ultrastructural changes in the mitochondria of Retzius' neuron exposed to hydrocortisone

The ultrastructure of the Retzius cell (gigantic neurone) mitochondria of the medical leech was investigated. After seven repeated injections of hydrocortisone into the coelomic cavity, the transformation of laminar cristae of mitochondria into tubule-vesiculated structures was discovered. A question of correlation between the structure and function independently of the systematical position of the organism is discussed.     

Ultrastructural changes in populations of the pertussis microbe exposed to antibiotics

The ultrastructural changes in the populations of the pertussis causative agent maintained for a prolonged period of time on nutrient media containing antibiotics were studied with the method of electron microscopy. Significant changes in the ultrastructure of the cells and the population composition due to the effect of tetracycline, levomycetin or erythromycin were observed. The ultrastructure of the populations affected by penicillin or streptomycin and their biological properties were most similar to those of the initial strains. The electronogrammes revealed morphological heterogeneity of the initial and experimental cultures and changes in the subpopulation composition induced by the antibiotics.     

Immunohistochemical demonstration of estradiol in the guinea pig ovary

Histochemical study of estradiol in the guinea pig ovary using RIA antiserum revealed specific estradiol fluorescence in theca interna cells and in single cells of atretic follicles. The fluorescence intensity was highest in the estrus phase.     

Ultrastructural changes of radish leaf exposed to cadmium

Cadmium (Cd²⁺) is one of the most toxic heavy metal pollutants in nature. Mesophyll cells from the leaf of radish seedlings exposed to 0.25 and 1.0 mM of CdCl₂ during 24 h exhibited structural changes of chloroplasts, mitochondria and nuclei when compared to non-treated control plants. Chloroplasts from Cd²⁺-exposed samples exhibited changes in the organelle shape, an increase in the stroma volume and a deposition of electron-dense material in the double membrane. The changes in the chloroplast membranes were not very drastic, however and reorganization of the thylakoids and stroma was observed. In contrast, the breakdown of the nuclear envelope of the plant cells treated with Cd²⁺ was very clear. The accumulation of electron-dense granules was also observed in mitochondria. No alterations were observed in the vacuoles of radish seedlings grown at different Cd²⁺ concentrations for the periods tested.     

Ultrastructural alterations in ciliary cells exposed to ionizing radiation

Summary Early effects of ionizing radiation were investigated in an experimental in vitro system using the ciliary cells of the tracheal mucous membrane of the rabbit, irradiated at 30° C and at more than 90% humidity. The changes in physiological activities of the ciliary cells caused by irradiation were continuously registered during the irradiation. The specimens were examined immediately after irradiation electron microscopically. The morphological changes in irradiated material after 10–70 Gy are compared with normal material. After 40–70 Gy, scanning electron microscopy revealed the formation of vesicles on cilia, and club-like protrusions and adhesion of their tips. After 30–70 Gy, a swelling of mitochondrial membranes and cristae was apparent transmission electron microscopically. The membrane alterations caused by irradiation are assumed to disturb the permeability and flow of ATP from the mitochondria, which in turn leads to the recorded changes in the activity of the ciliated cells.This investigation was supported by grants from Konung Gustaf V:s Jubileumsfond, John and Augusta Perssons Stiftelse, B. Kamprads Fond, the Faculty of Medicine, University of Lund, Sweden and the Swedish Medical Research Council (No. B77-17X-03897-05)The authors are greatly indebted to Miss Inger Norling, Miss Marianne Palmegren and Miss Birgitta Sandström for their excellent technical assistance