Ultrastructure of the plasmodial slime moldPerichaena vermicularis

Summary The development of the peridium ofPerichaena vermicularis has been examined using light and electron microscopy and acid phosphatase localization. A newly formed fruiting body consists of undifferentiated protoplasm which is enveloped by a slime coat. Almost immediately after formation of the plasmodiocarp, the protoplasm differentiates into autolytic and fruiting regions. The autolytic region is located at irregular intervals between the slime coat and the fruiting region and separated from both of them by membranes.Soon after the autolytic region has formed, additional signs of degeneration appear in the autolytic region including unusual appearance of nuclei, increase in autophagic vacuoles, and the presence of clear areas in the ground substance. The plasma membrane, which once completely separated the slime coat from the autolytic region, is no longer continuous. Electron micrographs of the autolytic region from later developmental stages show formation of extensive channels which contain protoplasm in various stages of degradation. Acid phosphatase is present in the channels of the autolytic region. The morphological evidence and the presence of hydrolytic enzyme suggest the region is being digested and re-adsorbed.After the autolytic region has been digested, an even layer of peridial wall material is laid down, and at regular intervals additional wall material is produced. The additional wall material forms the reticulation on the inside of the peridial wall.This work was supported by National Sciences Foundation grants (GB-5883 and GB-8537) to Dr.Ian K.Ross and an NSF Traineeship (GZ 445 and 796) to I.Charvat.This constitutes a portion of a thesis presented to the Regents of the University of California by the first author in partial fulfillment of the requirements for the Ph. D. degree.     

Peripheral Nerve-Derived CXCL12 and VEGF-A Regulate the Patterning of Arterial Vessel Branching in Developing Limb Skin

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Highlights? Cxcr4 is expressed by a subset of endothelial cells in the capillary network ? Genetic inactivation of Cxcl12-Cxcr4 signaling perturbs nerve-vessel alignment ? Cxcl12 controls endothelial migration, whereas VEGF directs arterial differentiation     

Molecular evolutionary dynamics of cytochrome b in strepsirrhine primates: the phylogenetic significance of third-position transversions

DNA sequences of the complete cytochrome b gene are shown to contain robust phylogenetic signal for the strepsirrhine primates (i.e., lemurs and lorises). The phylogeny derived from these data conforms to other molecular studies of strepsirrhine relationships despite the fact that uncorrected nucleotide distances are high for nearly all intrastrepsirrhine comparisons, with most in the 15%-20% range. Cytochrome b sequences support the hypothesis that Malagasy lemuriforms and Afro-Asian lorisiforms each comprise clades that share a sister- group relationship. A study (Adkins and Honeycutt 1994) of the cytochrome c oxidase subunit II (COII) gene placed one Malagasy primate (Daubentonia) at the base of the strepsirrhine clade, thereby suggesting a diphyletic Lemuriformes. The reanalysis of COII third- position transversions, either alone or in combination with cytochrome b third-position transversions, however, yields a tree that is congruent with phylogenetic hypotheses derived from cytochrome b and other genetic data sets.      

Functional differences between two structurally distinct types of steroidogenic cell in the avian adrenal gland

Summary There are two regions of steroidogenic cells in the duck adrenal gland. An outer, subcapsular zone (SCZ), consisting of cells with irregularly shaped nuclei, shows relatively little smooth endoplasmic reticulum and mitochondria with shelf-like cristae. This region surrounds the inner zone (IZ) of the gland which is comprised of smaller cells with rounded nuclei, a more abundant smooth endoplasmic reticulum and mitochondria with tubular cristae. When samples of tissue from these distinct regions of the gland are superfused in vitro with media containing concentrations of 1–24 ACTH ranging from 100 to 1000 ng per ml (0.034 to 0.34 M) the steroidogenic cells in both zones release corticosterone in a dose-dependent manner. The dose-responsiveness of both the SCZ and the IZ cells over this range is a complex quadratic function of the 1–24 ACTH concentration in the medium and the semilogarithmic linear portions of the dose-response curves are restricted to a narrow midrange of ACTH concentrations. Throughout the dose-response range, however, the steroidogenic cells of the IZ are more responsive to corticotropic stimulation than are the cells of the SCZ. The cells of the two zones are further distinguished by their responses to a challenge for a second time with medium containing 1–24 ACTH; the responses of the IZ cells to a second challenge were greater than those of the SCZ cells, and at a high concentration of ACTH the SCZ slices showed no significant second response.This work was supported by a grant from the National Science Foundation (PCM 79-15777) to James Cronshaw and W.N. Holmes     

The structural organization and the steroidogenic responsiveness in vitro of adrenal gland tissue from the neonatal mallard duck (Anas platyrhynchos)

Summary The adrenal steroidogenic tissue of the neonatal mallard duckling is differentiated into an outer subcapsular zone where the cells contain many large lipid droplets, and an inner zone in which the cells appear to contain less lipid. The cells in both zones contain numerous mitochondria and an abundance of smooth endoplasmic reticulum, and their interdigitating plasma membranes possess many filipodia, coated pits and desmosome-like junctions. Islands of chromaffin cells are distributed throughout the steroidogenic tissue. Two types of chromaffin cell are present, one with vesicles containing densely staining material and the other more lightly staining material. Non-myelinated preganglionic fibers synapse with the chromaffin cells and the axonal terminals contain two types of dense-cored vesicles as well as acetylcholine-containing vesicles. The basal rates of corticosterone (B) and aldosterone (Aldo) release from tissue superfused with buffer containing no secretogogue were low and almost equal (B: Aldo=1.25); the corresponding rate of deoxycorticosterone (DOC) release was less than one-fortieth of the rates of B and Aldo release. The addition of 1–24 ACTH to the medium caused the rate of release of each hormone to increase as a semi-logarithmic function of the concentration and the induced increase in B release was always significantly higher than that of Aldo (B: Aldo=4.8). The corticotropin-induced rates of B and Aldo, but not DOC, release reflected do novo hormone synthesis. Norepinephrine, epinephrine and dopamine each suppressed the basal rates of B and Aldo release, but had no effect when the medium contained 1–24 ACTH. Acetylcholine (ACh) similarly suppressed the basal rates of hormone release, and neither suppressed nor enhanced the responses to medium containing 1–24 ACTH. The suppressive effects of the catecholamines and ACh were not dose-related. [Asp¹, Val⁵] angiotensin II induced significant semi-logarithmic dose-dependent increases in Aldo synthesis but had no effect on the release of either B or DOC.This work was supported by grants to J. Cronshaw and W.N. Holmes from the University of California Committee on Research and the National Science Foundation (DIR-8820923), Washington, D.C., USA     

The effect of plant growth substances on the development of tension wood in horizontally inclined stems ofAcer rubrum seedlings

Summary In horizontally placedAcer rubrum seedlings the development of tension wood is inhibited by auxin especially when applied along the upper side of the axis. Treatment separately with GA and K does not alter the normal pattern of tension wood formation. The development of tension wood appears to be correlated with a reduced auxin level on the upper side of the stem.Geotropic reorientation of the woody stem ofAcer rubrum seedlings that are placed in the horizontal position is related closely to the amount of tension wood that is formed on the upper side of the axis. Evidence is discussed which indicates that tension wood itself participates actively in the reorientation mechanism.The following abbreviations will be used TIBA (2,3,5-tri-iodobenzoic acid) - IAA (indole-3-acetic acid) - GA (gibberellic acid) - NAA (naphthaleneacetic acid) - 2,4-D (2,4-dichloro-phenoxyacetic acid) - K (kinetin) This material was included in a doctoral thesis submitted by P. R.Morey to the graduate school of Yale University, New Haven.     

Fine structure of the aesthetasc hairs ofPagurus hirsutiusculus dana

Summary The thin-walled aesthetasc pegs on the antennules of a small hermit crab,Pagurus hirsutiusculus, were studied by light and electron microscopy. The lumen of each aesthetasc was found to be filled with the dendrites of 300–500 bipolar neurons whose cell bodies lie beneath the base of the aesthetasc. These dendrites are ciliary in nature, having well developed basal bodies and rootlets.Each basal body gives rise to a cilium which divides to form a cluster of slender branches, each of which contains a microtubule running lengthwise. These structures occupy most of the length of the hair.The cuticle of the aesthetasc wall is thin and tenuous. Except for the pore canals in the basal region, we have found no pores at either light or electron microscope level, but as the hair is extremely permeable, we conclude that the cuticle itself may permit the passage of solutions. This permeability of the cuticle and the large numbers of dendrites within support the hypothesis that the aesthetascs are chemoreceptors.     

A BIOCHEMICAL AND CYTOCHEMICAL STUDY OF ADENOSINE TRIPHOSPHATASE ACTIVITY IN THE PHLOEM OF NICOTIAN A TABACUM

A biochemical and cytochemical study has been made of the distribution of ATPase in mature and differentiating phloem cells of Nicotiana tabacum and of the substrate specificity and effects of fixation on enzyme activity. Homogenates of unfixed leaf midveins and midveins fixed in formaldehyde-glutaraldehyde were assayed for enzyme activity by determining the amount of P_i, liberated per milligram of protein from various substrates in a 30 min period at pH 7.2. In fresh homogenates, hydrolysis of ATP was not significantly different from that of ITP, CTP, and UTP. Hydrolysis of GTP was slightly higher than that of ATP. ATP hydrolysis by fresh homogenates was 17% more extensive than that of ADP, 76% more extensive than that of 5'-AMP, and was inhibited by fluoride and p-chloromercuribenzoate (PCMB). There was little or no hydrolysis of the competitive inhibitors 2'- and 3'-AMP nor with the alternate substrates p-nitrophenylphosphate (PNP) or β-glycerophosphate (β-GP). In homogenates of material fixed in formaldehyde-glutaraldehyde for 1¼ h, ATPase activity was 13% preserved. Hydrolysis of ATP by fixed homogenates was not significantly different from that of ADP, 5'-AMP, ITP, CTP, and GTP. Hydrolysis of UTP was lower. Fluoride and PCMB inhibited fixed ATPase activity. The results of cytochemical localization experiments using a lead phosphate precipitation technique were in agreement with the biochemical results. Similar localization patterns were obtained with the nucleoside triphosphates ATP, CTP, GTP, ITP, and UTP. Activity was also localized with ADP and 5'-AMP but not with the competitive inhibitors 2'- and 3'-AMP, nor with PNP or β-GP. Little or no reaction product was deposited in other controls incubated without substrate or with substrate plus fluoride, PCMB, or N-ethylmaleimide. ATPase activity was demonstrated chiefly at the plasma membrane of mature and differentiating phloem cells and was associated with the P-protein of mature sieve elements. It is suggested that the phloem transport system derives its energy from the demonstrated nucleoside triphosphatase activity.