Fasergabelung durch Auftreten lokalisierter Wachstumsbezirke

Summary The formation of forked fibres cannot be explained by the theories of sliding or of symplastic growth, while the theory of local apical growth of fibre ends accounts for all the actual facts observed in xylem and phloem fibres ofSparmannia africana. In this species cambium cells with a split end are found. These cells give rise to forked fibres, the forking point of which does not show any sliding growth, but remains on its original level. This evidence is undoubtedly a proof against the theory of sliding growth during fibre elongation inSparmannia.     

Analysis of <Emphasis Type="Italic">Dictyostelium</Emphasis> TACC reveals differential interactions with CP224 and unusual dynamics of <Emphasis Type="Italic">Dictyostelium</Emphasis> microtubules

We have localized TACC to the microtubule-nucleating centrosomal corona and to microtubule plus ends. Using RNAi we proved that Dictyostelium TACC promotes microtubule growth during interphase and mitosis. For the first time we show in vivo that both TACC and XMAP215 family proteins can be differentially localized to microtubule plus ends during interphase and mitosis and that TACC is mainly required for recruitment of an XMAP215-family protein to interphase microtubule plus ends but not for recruitment to centrosomes and kinetochores. Moreover, we have now a marker to study dynamics and behavior of microtubule plus ends in living Dictyostelium cells. In a combination of live cell imaging of microtubule plus ends and fluorescence recovery after photobleaching (FRAP) experiments of GFP-α-tubulin cells we show that Dictyostelium microtubules are dynamic only in the cell periphery, while they remain stable at the centrosome, which also appears to harbor a dynamic pool of tubulin dimers.     

Sekretomotorische Fasern und Endigungen in der Adenohypophyse

Summary We demonstrated, in the pituitary of the animals examined, fibres which emerge from the Tr. hypothalamo-hypophyseal system and enter partly into the Pars intermedia and partlyvia the Pars tubularis into the Pars distalis and take their course directly towards the glandular cells. In the Pars distalis the nerve fibres end around the glandular cells in a special pericellular net.     

Über einen Gradienten in der Samenschale vonCrepis capillaris bei der Keimung und seine mutmaßliche Bedeutung

Summary In the seed-coat ofCrepis capillaris a gradient is formed shortly before the germination. It consists in the growth of all the cells in a small, sharply delimited area at the end around the root-tip. This process takes place under a decrease of the thickness of the walls and a consumation of the reserve materials of the cells. The rest of the cells in the shell, which can not be distinguished from the cells of the pole during and after the swelling, remain at the same time unchanged. It is supposed that the gradient causes the germination of the root prior to the cotyledones. The investigations are being continued.     

Lipid droplets of neuroepithelial cells are a major calcium storage site during neural tube formation in chick and mouse embryos

In situ precipitation of calcium (Ca²⁺) with fluoride and antimonate shows that Ca²⁺-specific precipitate is localized almost exclusively within lipid droplets of neuroepithelial cells during neural tube formation in chick and mouse embryos. The density of Ca²⁺ precipitate within lipid droplets is generally greater in the apical ends of cells situated in regions of the neuroepithelium that are actively engaged in bending. These findings suggest that lipid droplets, in addition to providing a source of metabolic fuel for developing neuroepithelial cells, also serve as Ca²⁺-storage and-releasing sites during neurulation.This study was supported by grants from the NIH (NS23200), the BRSG fund of UMDNJ, and the Busch Fund of Rutgers University. Dr Bush was supported by a New Jersey State Postdoctoral Fellowship.     

Lysozymempfindlichkeit der SpeziesB. megaterium

Summary The 54 strains ofB. megaterium examined could be divided broadly into 2 groups on the basis of their lysozyme sensitivity. In most of the large-celled strains the cell walls were incompletely digested. Loss of turbidity on addition of lysozyme was comparatively slight and few free protoplasts were formed in the presence of saccharose. In contrast, the small-celled strains usually showed a marked drop in turbidity and complete protoplast formation could be obtained.These results suggest that, in some strains ofB. megaterium, particularly those possessing very large cells, certain substances are included in the cell walls which are not depolymerized by lysozyme.     

Elektronenmikroskopische Aufnahmen von Pollenschläuchen

Summary Electron micrographs were made of the cellulose part of the cell walls of pollen tubes ofPetunia hybrida, grown in selfed self-sterile plants and on agar plates. In sterile plants the tubes showed denser membranes but the orientation of the cellulose strands is the same as in cells germinated on agar.     

Zur Ultrastruktur des Herzschlauches vonCiona intestinalis L.

Summary The electron microscope structure of sectioned heart walls ofCiona intestinalis L. is described. The heart wall consists of one-layered epithelial muscle cells with cross-striated myofibrills, elongated long-shaped mitochondria and various cytoplasmic components.     

Isolation and properties of cell walls fromAgrobacterium tumefaciens B 6 1

Summary Purified cell walls were prepared fromAgrobacterium tumefaciens B ₆ by extraction of intact cells with hot sodium dodecyl sulfate and digestion with proteases. Such preparations contained peptidoglycan that accounted for about 40% of their dry weight. Electron micrographs of the purified walls showed that they conserved their characteristic shape despite the drastic extraction procedure.This work was supported in part by a contribution from a friend of the Weizmann Institute of Science in Buenos Aires, Argentine.I wish to thank Professor Nathan Sharon for his constant interest and critical discussion during this work.     

Nuclear fusion and irregular cytokinesis in binucleate and tetraploid cells ofVicia faba after caffeine treatment

Summary By means of 3 h treatment with 0.2% caffeine solution, binucleate and tetraploid cells were obtained in the lateral root meristem ofVicia faba. During recovery changing rates of fused interphases were noticed. Cell walls were formed in the equatiorial plane of the preceeding division of binucleate and tetraploid cells at interphase and in the course of bimitosis or 4n-mitosis at prophase or metaphase; during bitelophase a constriction of the fused nuclei could be seen. The conclusion is that the basic requirements of cytokinesis are not affected by caffeine.     

A histochemical study of the pectoralis muscle of the south indian flying lizard,Draco dussumieri

Résumé Le muscle pectoral duDraco dussumieri comprend des fibres de trois sortes: minces, intermédiaires et épaisses. Les fibres minces sont adaptées à un métabolisme glycolytique et les fibres épaisses au lipolytique. L'activité des fibres minces révèle la présence de phosphorylase et de synthétase glycogénique.     

Ultrastructure of muscle spindles in C57BL/6Jdy 2J/dy 2J dystrophic mice

Summary The sensory organs of skeletal muscles, the muscle spindles, were examined using electron microscopy indy ^2J/dy ^2J dystrophic mice. Despite widespread damage to the extrafusal (skeletomotor) fibres the intrafusal (spindle) fibres appeared normal and seemed resistant to the aetiological factors for murine dystrophy.This work was supported by grants from the Medical Research Council and the Science Research Council of Great Britain.     

Neuer Beitrag zur Determination der Imaginalscheiben beiDrosophila

Summary The temperature effective period for the formation of double antennæ and palpi in the gene-combinationsc ec ct; Dfd ^r-L ends with the second half of the third larval stage. The t.e.p. of the mutantsaristopedia andproboscipedia ends with puparium formation. Thus we have another proof that the imaginal discs ofDrosophila are not definitely determined in the last larval stage.     

Redundant regulation of localization and protein stability of DmPar3

Apical–basal polarity is an important characteristic of epithelia and Drosophila neural stem cells. The conserved Par complex, which consists of the atypical protein kinase C and the scaffold proteins Baz and Par6, is a key player in the establishment of apical–basal cell polarity. Membrane recruitment of Baz has been reported to be accomplished by several mechanisms, which might function in redundancy, to ensure the correct localization of the complex. However, none of the described interactions was sufficient to displace the protein from the apical junctions. Here, we dissected the role of the oligomerization domain and the lipid-binding motif of Baz in vivo in the Drosophila embryo. We found that these domains function in redundancy to ensure the apical junctional localization of Baz: inactivation of only one domain is not sufficient to disrupt the function of Baz during apical–basal polarization of epithelial cells and neural stem cells. In contrast, mutation of both domains results in a strongly impaired protein stability and a phenotype characterized by embryonic lethality and an impaired apical–basal polarity in the embryonic epithelium and neural stem cells, resembling a baz-loss of function allele. Strikingly, the binding of Baz to the transmembrane proteins E-Cadherin, Echinoid, and Starry Night was not affected in this mutant protein. Our findings reveal a redundant function of the oligomerization and the lipid-binding domain, which is required for protein stability, correct subcellular localization, and apical–basal cell polarization.     

Protein-O-mannosyltransferases in virulence and development

Protein-O-mannosyltransferases (Pmt proteins) catalyse the addition of mannose to serine or threonine residues of secretory proteins. This modification was described first for yeast and later for other fungi, mammals, insects and recently also for bacteria. O-mannosylation depends on specific isoforms of the three Pmt1, 2 and 4 subfamilies. In fungi, O-mannosylation determines the structure and integrity of cell walls, as well as cellular differentiation and virulence. O-mannosylation of specific secretory proteins of the human fungal pathogen Candida albicans and of the bacterial pathogen Mycobacterium tuberculosis contributes significantly to virulence. In mammals and insects, Pmt proteins are essential for cellular differentiation and development, while lack of Pmt activity causes Walker-Warburg syndrome (muscular dystrophy) in humans. The susceptibility of human cells to certain viruses may also depend on O-mannosyl chains. This review focuses on the various roles of Pmt proteins in cellular differentiation, development and virulence. Received 6 September 2007; received after revision 3 October 2007; accepted 5 October 2007     

β-(6-Bromopyridin-3-yl)alanine. A new plant growth regulator

Summary The heterocyclic amino acid, -(6-bromopyridin-3-yl)alanine [DL-a-amino--(6-bromopyridin-3-yl)propanoic acid], interferes with the morphological development of the cruciferArabidopsis thaliana when incorporated in the growth medium. It appears to overcome the normal apical dominance control mechanism within the seedling, producing multirather than single-stemmed plants.     

Quelques aspects de la croissance rhizomorphique chez leSphaerostilbe repens

Summary The rhizomorphs ofSphaerostilbe repens attached to synnemata and mycelia or severed from them, grew providing that their apices were kept inside the culture medium. Exposed to air, apical regions became dark brown, stopped growing and differentiated into synnemata. However central canals in the middle of the rhizomorphs had to be continuously maintained in contact with the atmosphere; nitrogen immediately stopped rhizomorphic growth. This indicates that oxygen for growing apices is supplied through central canals and that the partial pressure of oxygen has to be higher at the origin of the rhizomorphs than that which is in contact with the outside surfaces of their apices.     

Ultrastructure of 30–40 million year old leaflets from Dominican amber (Hymenaea protera,Fabaceae: Angiospermae)

Hymenaea protera leaflet fossils entombed in amber, dated at 30 to 40 million years (mine strata and exomethylene dating) were observed by both light and transmission electron microscopy. Ultrastructure preservation in these leaflets shows the presence of chloroplasts with thylakoid membranes, cell walls, mitochondria with associated endoplasmic reticulum, nuclei, and xylem tissue. Tissues show varying degrees of degradation; however, natural resin, which has perfused the cells, seems to maintain the structural integrity of the membranes and walls. We conclude that preservation of amber entombed organisms results from dehydration and slow fixative properties leaving the ultrastructure in excellent condition. These findings parallel reports on the exceptional preservation of amino acids and of DNA in amber-entombed organisms.     

Effects of mistletoe (Viscum album L.) extracts on cultured tumor cells

Summary Bacterially fermented mistletoe preparations (BFMP) were tested on rat hepatoma tissue culture (HTC) cells and human leukemia Molt 4 cells. A dose-dependent inhibition of the growth rate of the cells was observed. For both cell lines, cytostatic concentrations, expressed in weight of fresh plant, were 0.5 mg/ml culture medium for oak BFMP and 1 mg/ml for apple tree BFMP. However, the action of the two preparations was markedly different on each cell line. Non-viable HTC cells were not stained by trypan blue while non-viable Molt 4 cells were fully colored by this reagent. A lysis of cellular membranes of HTC cells was observed by electron microscopy. Furthermore, oak BFMP inhibited the growth of virus transformed 3T3-SV40 cells more than that of non-transformed 3T3 cells. In contrast to BFMP, non-fermented extracts and a purified mistletoe lectin showed a greater inhibition of the growth of Molt 4 cells than of HTC cells. Samples withdrawn at different times during fermentation gradually lost their inhibitory effect on the growth of Molt 4 cells while their action on HTC cells increased up to the 4th day of fermentation. These results are discussed in relation to the cytotoxic substances of mistletoe already characterized.The bacterially fermented mistletoe preparations, named BFMP in the text, were obtained from the Hiscia Institute, CH-4144 Arlesheim, Switzerland, under the name of Iscador. For oak BFMP, mistletoe was fromQuercus petraea Liebl. andQuercus robur L.; for apple tree BFMP fromMalus domestica Borkh.     

Telomeres and DNA double-strand breaks: ever the twain shall meet?

Telomeres were first recognized as a bona fide constituent of the chromosome based on their inability to rejoin with broken chromosome ends produced by radiation. Today, we recognize two essential and interrelated properties of telomeres. They circumvent the so-called end-replication problem faced by genomes composed of linear chromosomes, which erode from their termini with each successive cell division. Equally vital is the end-capping function that telomeres provide, which is necessary to deter chromosome ends from illicit recombination. This latter property is critical in facilitating the distinction between the naturally occurring DNA double-strand breaks (DSBs) found at chromosome ends (i.e., telomeres) and DSBs produced by exogenous agents. Here we discuss, in a brief historical narrative, key discoveries that led investigators to appreciate the unique properties of telomeres in protecting chromosome ends, and the consequences of telomere dysfunction, particularly as related to recombination involving radiation-induced DSBs. Dedication. In appreciation of his heart-felt commitment to research and education, and the life-long influence he has had on the lives of students and colleagues, the authors wish to dedicate this paper to Professor Joel S. Bedford. Received 21 May 2007; received after revision 28 June 2007; accepted 6 August 2007