The Effect of Hydrocortisone on the Epidermal Proliferation in an Organ Culture of Chick Embryonic Skin

Hydrocortisone is regarded as an initiator of keratinization in embryonic skin. The present investigation dealt with the effect of hydrocortisone on the proliferation of epidermal cells during early development: Cell kinetic analyses using ³H-thymidine autoradiography were applied to a skin organ culture prepared from a 13-day chick embryo.
Hydrocortisone at a concentration between 0.01 and 1.0 μg/ml was effective in initiating a morphological change leading to the epidermal keratinization in vitro and caused a marked decrease in the mitotic and labeling indices of epidermal basal cells, the decrease being maximum at 2 days of culture previous to the morphological change.
During continuous labeling with ³H-thymidine, the number of labeled basal cells reached 100% within 2 days in the control and 4 days in the culture treated with hydrocortisone. This confirmed that the growth fraction of epidermal basal cells was 1.0 even after the administration of hydrocortisone.
The duration of each cell cycle phase at 2 days of culture was determined by percent labeled mitoses and double-labeling analyses. It was concluded that hydrocortisone extended the generation time of epidermal basal cells at this time point about three fold over the control. This extension was mainly due to the elongation of the G ₁ phase.     

Changes in Total Nitrogen and Free Amino Acids in Stem Cuttings of Mulberry (Morus alba L.)

Changes in total nitrogen and free amino acid contents in stemcuttings of Morus alba have been studied. The fresh and dryweights and total nitrogen amounts of the parent stems of cuttingsdecreased initially after cutting. Their increase follows theformation of main roots in cuttings, suggesting that, like carbohydrates,sugars and starch, stored nitrogenous substances are used forsprouting and rooting of cuttings. Amino acids found in stems,roots and shoots are those common in other higher plants withthe exception of pipecolic acid and 5-hydroxypipecolic acid.Significant changes in the levels of asparagine, proline, arginine,-aminobutyric acid and alanine in roots, bark and wood of parentstems were observed during cutting growth, whereas those ofother amino acids remained comparatively constant; the mostpredominant amino acid in the starting materials was proline.while that in the cuttings during growth was asparagine. Theresults suggest that, among free amino acids, asparagine, prolineand arginine play the major part in storage of nitrogen in mulberry.The importance of glut-amine and asparagine in nitrogen metabolismin mulberry has been discussed.     

CHANGES OF THE MEMBRANE POTENTIAL AT THE TIME OF FERTILIZATION IN THE SEA URCHIN EGG WITH SPECIAL REFERENCE TO THE FERTILIZATION-WAVE

An experimental device was developed from the work of U ehara and S ugiyama (1969), in order to study the electrical phenomena accompanying the fertilization-wave in the sea urchin egg.
The change in membrane potential upon fertilization consists of 2 peaks (I to et al. , 1970), being preceded by a shoulder. The shoulder appears within the "latent period" (A llen and G riffin , 1958), and the 2 peaks correspond to the breakdown of the cortical granules and the formation of the fertilization membrane.
When the equatorial region of the egg surface was exposed to a detergent-sea water, the breakdown of the cortical granules and the formation of the fertilization membrane are induced only in this ring-shaped area. Sperm is then added to one of the polar regions. The fertilization-wave, starting from the point of sperm-entry, propagates across the detergent-treated region, and the membrane is formed on the whole egg surface. During such an experiment, changes of the membrane potential in the detergent-treated region were measured. 1 to 3 sudden transient depolarizations appear, followed by a delayed small depolarization. It is presumed that the initial depolarization corresponds to the fertilization-wave. The pattern of the potential change at normal fertilization may be explained by complexity of the cortical change, and the initial depolarizing shoulder is considered to correspond to the fertilization-wave, which is isolated by the above-mentioned device.     

EXPERIMENTAL STUDIES ON THE SITE OF PROPAGATION OF THE FERTILIZATION-WAVE IN THE SEA URCHIN EGG

Although the fertilization-wave in the sea urchin egg is generally considered to propagate over the egg surface, there has been no definite evidence to show the site of propagation. The possibility that the wave passes through the endoplasm, not over the egg surface, has not been denied.
A drop of paraffin was injected into an egg, so that the endoplasm was divided into 2 parts by the paraffin drop, the 2 parts being connected only by the egg cortex. When spermatozoa were added to one side of the egg, the fertilization membrane was formed first on this part of the egg and then on the opposite part. This indicates that the egg surface or the egg cortex is the site of propagation of the fertilization-wave and the endoplasm has no direct influence on the propagation.     

DISTRIBUTION OF MATURATION-PROMOTING FACTOR IN STARFISH OOCYTE STRATIFIED BY CENTRIFUGATION

In starfish, cytoplasm taken from maturing oocytes is capable of inducing breakdown of the germinal vesicle and subsequent maturation when injected into immature oocytes. The cytoplasmic factor has been designated as "maturation-promoting factor" (MPF). Ooplasm was stratified by centrifugation of maturing oocytes in density-graded Ficoll-seawater, without disrupting the cell. Three strata were distinguished beginning with the centripetal side: oil cap, hyaline layer and yellow layer. MPF activity was shown to be localized in the hyaline layer. Electron microscopic observation revealed that the hyaline layer contains Golgi complexes, many lucent vesicles and multi-vesicular bodies as distinct organelles, but seldom contains such inclusions as the lipid droplets forming the oil cap, mitochondria, yolk and pigment granules contained in the yellow layer. Based on these observations, a possible cytoplasmic component with MPF activity is discussed.     

Ion gradients in xylem exudate and guttation fluid related to tissue ion levels along primary leaves of barley

The concentration of ions in plant cells and tissues is an essential factor in determining physiological function. In the present study, we established that concentration gradients of mobile ions exist in both xylem exudates and tissues within a barley (Hordeum vulgare) primary leaf. For K⁺ and NO₃^?, ion concentrations generally decreased from the leaf base to the tip in both xylem exudates and tissues. Ion gradients were also found for Pi and Cl^? in the xylem. The hydathode strongly absorbed Pi and re‐translocated it to the rest of the plant, whereas Cl^? was extruded. The ion concentration gradients developed early during leaf growth, increased as the tissue aged and remained under both high and low transpiration conditions. Measurement of the expression profiles of Pi, K⁺ and NO₃^? transporters along the longitudinal axis of the leaf revealed that some transporters are more expressed at the hydathode, but for most transporters, there was no significant variation along the leaf. The mechanisms by which longitudinal ion gradients develop in leaves and their physiological functions are discussed.     

Phylogenetic analysis of the Brazilian microendemic Paepalanthus subgenus Xeractis (Eriocaulaceae) inferred from morphology

Paepalanthus subgenus Xeractis (Eriocaulaceae) comprises 28 recognized species endemic to the Espinhaço Range, in Minas Gerais state, Brazil. Most species of the subgenus are restricted to small localities and critically endangered, but still in need of systematic study. The monophyly of the subgenus has already been tested, but only with a few species. Our study presents the first phylogenetic hypothesis within the group, based on morphology. A maximum parsimony analysis was conducted on a matrix of 30 characters for 30 terminal taxa, including all species of the subgenus and two outgroups. The biogeographical hypotheses for the subgenus were inferred based on dispersal–vicariance analysis (DIVA). The analysis provided one most‐parsimonious hypothesis that supports most of the latest published subdivisions (sections and series). However, some conflicts remain concerning the position of a few species and the relationships between sections. The distribution and origin(s) of microendemism are also discussed, providing the ground for conservation strategies to be developed in the region. © 2011 The Linnean Society of London, Botanical Journal of the Linnean Society, 2011, 167 , 137–152.     

INDUCTION OF OOCYTE MATURATION BY DISULFIDE-REDUCING AGENT IN THE SEA CUCUMBER, STICHOPUS JAPONICUS

1-Methyladenine (1-MeAde) is known to be a natural inducer of starfish oocyte maturation. Disulfide-reducing agents such as dithiothreitol (DTT) and 2, 3-dimercapto-1-propanol (BAL) are known to mimic the action of 1-MeAde in inducing starfish oocyte maturation. Although 1-MeAde failed to induce oocyte maturation in sea cucumbers, breakdown of germinal vesicles and subsequent meiotic behaviour of chromosomes were induced by the treatment with DTT in the pronase-treated oocytes of the sea cucumber, Stichopus japonicus. These findings suggest that reduction of disulfide bonds plays an important role in triggering oocyte maturation in some marine forms such as echinoderms.     

Oocyte Competence to Maturation-inducing Hormone. I. Breakdown of Germinal Vesicles of Small Oocytes in Starfish,Asterina pectinifera*

1-Methyladenine (1-MeAde) is the endogenous maturation-inducing substance (MIS) in starfish. However, small oocytes have no competence to 1-MeAde even at the concentration of 10^?5M. Furthermore, when they were injected with cytoplasm of fully-grown (large) and maturing (1-MeAde-treated) oocytes, known to contain maturation-promoting factor (MPF), they did not undergo germinal vesicle breakdown (GVBD). On the other hand, germinal vesicles (GV) of the small oocytes underwent nuclear breakdown when the small oocytes were fused with the large maturing oocytes. Therefore it is concluded that the GV of the small oocytes are capable of undergoing nuclear breakdown in the presence of the sufficient MPF, but that the small oocytes can not amplify the injected MPF. Fused cells displayed particular shape changes during the course of nuclear breakdown of both the large and the small oocytes.