Adaptations for matrotrophy in the female reproductive system in the pseudoscorpion Chelifer cancroides (Chelicerata: Pseudoscorpiones,Cheliferidae)

Pseudoscorpiones (pseudoscorpions, false scorpions) is an order of small terrestrial chelicerates. While most chelicerates are lecithotrophic, that is, embryos develop due to nutrients (mostly yolk) deposited in the oocyte cytoplasm, pseudoscorpions are matrotrophic, that is, embryos are nourished by the female. Pseudoscorpion oocytes contain only a small amount of yolk. The embryos develop within a brood sac carried on the abdominal site of the female and absorb nutrients by a pumping organ. It is believed that in pseudoscorpions nutrients for developing embryos are produced in the ovary during a postovulatory (secretory) phase of the ovarian cycle. The goal of our study was to analyze the structure of the female reproductive system during the secretory phase in the pseudoscorpion Chelifer cancroides, a representative of the family Cheliferidae, considered to be one of the most advanced pseudoscorpion taxa. We use diverse microscopic techniques to document that the nutritive fluid is produced not only in the ovaries but also by the epithelial cells in the oviducts. The secretory active epithelial cells are hypertrophic and polyploid and release their content by fragmentation of apical parts. Our observations also indicate that fertilization occurs in the oviducts. Moreover, in contrast to previous findings, we show that secretion of the nutritive material starts when the fertilized oocytes reach the brood sac and thus precedes formation of the pumping organ. Summing up, we show that C. cancroides exhibits traits of advanced adaptations for matrotrophy due to coordinated secretion of the nutritive fluid by the ovarian and oviductal epithelial cells, which substantially increases the efficiency of nutritive fluid formation. Since the secretion of nutrients starts before formation of the pumping organ, we suggest that the embryos are able to absorb the nutritive fluid also in the early embryonic stages.     

The Effect of Various Culture Media on the Formation of Embryo-like Structures in Cultures Derived from Explants Taken from Mature Larix decidua

The effect of various collection dates and nine different culture media on the formation of ‘embryo-like structures’ (ELS) in cultures derived from explants taken from a 42-year-old Larix decidua tree was studied. The best medium was AFC, a medium low in NH₄⁻, NO₃ ⁺, Mg²⁺ and SO₄²⁻ but high in PO₄³⁻ compared with the concentration of these elements in the other media. On AFC, ELS production reached a peak with collections made in late summer during the period when needle primordia are being initiated. For the other media, collection date had a lesser effect on ELS initiation.     

Pollen genotype selection for a simply inherited qualitative factor determining resistance to chlorsulfuron in maize

Pollen genotype selection for genes expressed in both the haploid and diploid phases of the plant life cycle can lead to correlated responses detectable in the sporophyte. A pollen selection was conducted in two genetic backgrounds of maize (Zea mays L.) for chlorsulfuron resistance, conferred by the XA17 allele. Plants of two backcross (BC) lines segregating 1 (heterozygote, resistant) : 1 (homozygote, susceptible) for chlorsulfuron resistance were used as pollen donor. Selection treatment was applied during microspore development, and tassels were cut about 10 days before anthesis and placed into a liquid medium with or without 40 mg l^–1 of chlorsulfuron. Pollen was used to fertilize an unrelated susceptible genotype (tester). The resulting testcrosses (TC) were evaluated in the greenhouse by spraying seedlings with chlorsulfuron at 23 g ha^–1. Non-selected TC progenies derived from heterozygous BC plants showed a proportion of resistant and susceptible plants close to the expected 1:1 ratio, while non-selected TC progenies derived from homozygous BC plants showed susceptible plants only. Selected TC progenies derived from heterozygous BC plants showed a frequency of resistant plants ranging from 89% to 100%. BC plants homozygous for the susceptible allele, subjected to selection treatment, gave poor seed set, and no resistant plants were found in their TC progenies. Resistant TC plants obtained through pollen genotype selection were selfed, and the proportion of resistant plants was close to 3:1 in all selfed families, in accordance with the hypothesis that all of them inherited the XA17 allele through selection. In this study, pollen genotype selection was extremely effective, and its effect persisted in the second sporophytic generation. Received: 19 November 1999 / Accepted: 30 April 2000     

Control of in vitro somatic embryogenesis of the spindle tree (Euonymus europaeus L.) by the sugar type and the osmotic potential of the culture medium

 In vitro somatic embryogenesis was achieved from zygotic embryo explants of a woody angiosperm species, the spindle tree, cultivated on various culture media differing in their sugar type and concentration, or in the applied osmotic potential. The highest frequency of somatic embryogenesis was obtained with a 350 mM sucrose, or a 89 mM glucose concentration in the culture medium. Experiments with culture media differing only in osmotic potential indicated that a minimal threshold osmotic potential is required to stimulate the emergence of somatic embryos. Elevated concentrations of glucose have an inhibitory effect, independent of their osmotic effect, while elevated concentrations of sucrose mainly act osmotically, stimulating the emergence of numerous somatic embryos. Received: 15 July 1997 / Revision received: 27 October 1997 / Accepted: 24 March 1998     

Focal adhesion kinase is abundant in developing blood vessels and elevation of its phosphotyrosine content in vascular smooth muscle cells is a rapid response to angiotensin II

Focal adhesion kinase (FAK) is a structurally unique nonreceptor protein-tyrosine kinase that localizes to focal adhesion plaques. Regulation of its activity has been implicated in diverse signaling pathways, including those mediated by extracellular matrix/integrin interactions, G-protein coupled receptors for mitogenic neuropeptides, and certain oncogene products. To gain evidence for specific processes in which FAK may be involved in vivo, a study was initiated to determine its expression pattern during mouse development. FAK expression was detected in early embryos and appeared to be distributed throughout all cell types at about the time of neurulation. Subsequent to neural tube closure, expression became particularly abundant in the developing vasculature. This included expression in the medial layer of arteries populated by smooth muscle cells. In vitro studies using cultured rat aortic vascular smooth muscle cells demonstrate that FAK phosphotyrosine content is dramatically elevated in response to plating cells onto the adhesive glycoprotein, fibronectin. Also, enhanced tyrosine phosphorylation of FAK is observed in these cells upon stimulation with the vasoconstrictor angiotensin II. Thus, in vascular smooth muscle cells, like fibroblasts, FAK appears to play a role in signaling mechanisms induced by extracellular matrix components as well as G-protein coupled receptor agonists. The combined results of this study suggest that signaling through FAK may play an important role in blood vessel morphogenesis and function. © 1994 Wiley-Liss, Inc.     

Competence of blastomeres for the expression of molecular tissue markers is acquired by diverse mechanisms in the embryo of Platynereis (Annelida)

This paper is devoted to the role of cell divisions for the establishment of histospecificity in the embryo of the spiralian, Platynereis dumerilii (Annelida). We have incubated successive cleavage stages in cytochalasin B (CCB) and observed whether the cells thereafter were able to acquire the competence for expressing histospecific antigens of larval gland cells (labelled by the monoclonal antibody OI64) and of neural components of the ventral nerve cord (labelled by mAb OI7 or by testing acety1cholinesterase activity), respectively. Incubation in CCB results in permanent cleavage arrest, but does not necessarily interfere with biochemical differentiation of such markers. Synthesis of the differentiation marker specific for larval gland cells does not require any cleavages but this capacity becomes restricted to the 1a and 1b cell lines if cleavages are allowed to occur. In contrast, the progenitors of neural cells need at least 6.5 h of normal development before they acquire the competence to synthesize two neural differentiation markers, which can be demonstrated after at least two more days of development. Thus, prespecifying and diversifying cleavages are a prerequisite for neurogenesis and production of the investigated neural markers. Competence for the expression of histospecific antigens may also depend on cell-cell interactions. If 20–24 h old embryos are treated with puromycin, pioneering fibres fail to grow out from a pair of posterior nerve cell progenitors as they would have done normally 24–48 h after fertilization. Concomitantly, a number of potential nerve cells which now do not come into contact with pioneering fibres do not express the neural antigen. This suggests that a local inductive stimulus from the pioneering fibres normally imprints cell fate onto ventral plate cells and turns them into neuroblasts. Correspondence to: A.W.C. Dorresteijn     

A novel type of FKBP in the secretory pathway of Neurospora crassa

FKBPs define a subfamily of peptidyl-prolyl cis/trans isomerases (PPIases). PPIases are known to play roles in cellular protein folding, protein interactions and signal transduction. Here we describe NcFKBP22 from Neurospora crassa, a novel type of FKBP. NcFKBP22 is synthesized as a precursor protein with a cleavable signal sequence. In addition to a typical FKBP domain in the amino-terminal part mature NcFKBP22 contains a novel second domain which is unique amongst all known FKBPs. The amino acid composition of this carboxy-terminal domain is highly biased. Secondary structure predictions suggest that this domain may form an amphipathic α-helix. The carboxy-terminus of NcFKBP22 is –HNEL, a potential endoplasmic reticulum (ER) retention signal, suggesting that NcFKBP22 is a resident protein of the ER.     

Independent parental contributions initiate zygote polarization in Arabidopsis thaliana

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