Factors controlling somatic embryogenesis

Histological and ultrastructural, molecular and elemental distribution changes were investigated during the induction of direct somatic embryogenesis using theCamellia japonica leaf culture system. In this culture system, direct somatic embryogenesis is induced in a controlled way in a specific leaf region (leaf blade) within a leaf. Embryogenic and non-embryogenic leaf regions have characteristic energy-dispersive X-ray spectra already before induction. According to these results electron probe X-ray microanalysis (EPMA) can be a tool for early diagnosis of embryogenic competence. Histological studies showed that severe fluctuations in the number of calcium oxalate crystals and in starch accumulation occur after induction but only in induced tissues. Changes in the cell wall composition of competent cells occur shortly after the induction treatment. The induction of morphogenesis is linked to the appearance of callose covering the surface cells of induced leaves and calluses. A 2^nd deposition of material (cutin) is necessary for normal somatic embryogenesis to occur. The involvement of lipid transfer proteins in the appearance of cutin in the embryogenic regions of the explant is suggested.     

Influence of external factors on secondary embryogenesis and germination in somatic embryos from leaves of Quercus suber

Somatic embryogenesis was obtained in cultures of leaves from young seedlings of Quercus suber L. A two-stage process, in which benzyladenine and naphthaleneacetic acid were added first at high and then at low concentrations, was required to initiate the process. Somatic embryos arose when the explants were subsequently placed on medium lacking plant growth regulators. The embryogenic lines remained productive, by means of secondary embryogenesis, on medium without growth regulators. However, this repetitive induction was influenced by the macronutrient composition of the culture medium. Both low total nitrogen content and high reduced nitrogen concentration decreased the percentage of somatic embryos that showed secondary embryogenesis. Our results suggest that alternate culture on medium that increases embryo proliferation and a low salt medium prohibiting embryo formation will partially synchronize embryo development. Chilling slightly reduced secondary embryogenesis but gave a modest increase in germination. Maturation under light followed by storage at 4 °C for at least 30 days gave the best results in switching embryos from an embryogenic pathway to a germinative one. Under these conditions 15% of embryos showed coordinated root and shoot growth and 35% formed either shoots or mostly roots. These percentages were higher than those of embryos matured in darkness. This result indicates that a specific treatment is required after maturation and before chilling to activate the switch from secondary embryo formation to germination.Abbreviations BA benzyladenine - NAA naphthaleneacetic acid - 2,4-D 2,4-dichlorophenoxyacetic acid - BA indolebutyric acid - MS Murashige & Skoog (1962) medium - SH Schenk & Hildebrandt (1972) medium - G Gamborg (1966, PRL-4-C) medium (macronutrients in mg l^–1: NaH₂PO₄·H₂O, 90; Na₂HPO₄, 30; KCl, 300; (NH₄)₂SO₄, 200; MgSO₄·7H₂O, 250; KNO₃, 1000, CaCl₂·2H₂O, 150) - PGR plant growth regulator     

Analysis of vertical ozone and nitrogen oxides profiles in aPrunus cerasifera canopy

An automatic system was installed for continuous analyses of ozone, sulphur dioxide, nitrogen monoxide and nitrogen dioxide in an experimental orchard with a canopy ofPrunus cerasifera plants in summer 1993. Air samples from three elevations (0.8 m, 1.6 m and 3 m above ground) were sequentially analyzed. Ozone concentrations above the canopy were usually higher than within the canopy; their relationships with stomatal resistance have been investigated. Sulphur dioxide levels were negligible. Nitrogen oxides showed a complex profile, with no particular trend, likely due to a reciprocal exchange between the atmosphere and the ground surface.     

Synthesis and biological evaluation of novel NK-1 tachykinin receptor antagonists: The use of cycloalkyl amino acids as a template

In the course of a program aimed at synthesizing novel, potent NK-1 tachykinin receptor antagonists, we developed upon a bioactive model by comparing the low energy structures of a series of peptide and nonpeptide Substance P antagonists. The comparison was based on the super imposition of the aromatic rings, assuming that the rest of the molecule behaves predominantly as a template to arrange the key aromatic groups in the right spatial position. A series of 2-aminocyclohexane carboxylic acid analogues were then selected as the best templates for reproducing the postulated bioactive structure, leading to several pseudo-peptides with interesting biological activity. According to the molecular modeling, these compounds exhibit a neat parallel facing of the indolyl and naphthyl groups at about 3 Å distance. Ultraviolet absorption and steady state fluorescence measurements support this conclusion, showing a linear correlation between the spectral properties and the binding affinity of these analogues. Stacking of the indole ring with naphthalene gives rise to a complex characterized by a well-defined molar extinction coefficient. Consistently, steady state and lifetime fluorescence measurements suggest that the quenching process is ascribable to ground-state interactions between the chromophores. Implications of the π stacking propensity of aromatic groups in the biological activity of the compounds examined are briefly discussed. © 1995 John Wiley & Sons, Inc.     

Maintenance of transposable element copy number in natural populations of Drosophila melanogaster and D. simulans

To investigate the main forces controlling the containment of transposable elements (TE) in natural populations, we analyzed the copia, mdg1, and 412 elements in various populations of Drosophila melanogaster and D. simulans. A lower proportion of insertion sites on the X chromosome in comparison with the autosomes suggests that selection against the detrimental effects of TE insertions is the major force containing TE copies in populations of Drosophila. This selection effect hypothesis is strengthened by the absence of the negative correlation between recombination rate and TE copy number along the chromosomes, which was expected under the alternative ectopic exchange model (selection against the deleterious rearrangements promoted by recombination between TE insertions). A cline in 412 copy number in relation to latitude was observed among the natural populations of D. simulans, with very high numbers existing in some local populations (around 60 copies in a sample from Canberra, Australia). An apparent absence of selection effects in this Canberra sample and a value of transposition rate equal to 1–2 × 10^-3 whatever the population and its copy number agree with the idea of recent but temporarily drastic TE movements in local populations. The high values of transposition rate in D. simulans clearly disfavor the hypothesis that the low amount of transposable elements in this species could result from a low transposition rate. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of lipids on activity and conformation of lysolecithin:lysolecithin acyltransferase from rabbit lung

Summary Lysolecithin:lysolecithin acyltranferase is an enzyme which in several previous studies has shown a dual behavior catalyzing two types of reaction, transacylation or hydrolysis, with the same substrate. Both activities have shown to be dependent on several environmental conditions and among them, the presence of lipids.The addition of several classes of lipids activated in all the cases the enzyme, decreasing the hydrolysis/transacylation molar ratio. This effect was higher for PC/PE/Chol mixture than for other lipids assayed. Circular dichroism spectra of the enzyme did not show any change with the addition of lipids, concluding that the effect of lipids was not due to any structural change in the protein. The hypothesis has been made of an influence of lipids on the physical state of the substrate as well as, possibly, on the enzyme-substrate interaction.The significance of these effects on the physiological role of lysolecithin:lysolecithin acyltransferase from soluble fraction of rabbit lung is discussed.Abbreviations Chol cholesterol - CMC critical micellar concentration - DPPC dipalmitoylphosphatidylcholine - FA fatty acid - H/T hydrolysis/transacylation molar ratio - LPC lysophosphatidylcholine - PC phosphatidylcholine - PE phosphatidylethanolamine - TG triglyceride - UV ultraviolet     

Triplex gene dosage effect for β-glucronidase and possible assignment to band q22 in a partial duplication 7q

Summary A 2-year-old girl had a de novo duplication in the long arm of one chromosome 7 and an increased level of the enzyme -glucuronidase in cultured fibroblasts. The phenotype of the girl partly overlaps those of two presumptive syndromes due to secondary partial trisomies 7q. The ratio of the enzyme activity was 1.43 to the controls, and 1.37 to her parent's values. We could not define the abnormality but suggest two alternatives: either the patient is trisomic for region q112 to q22 or for the region q22 to q34. If the second alternative is correct the locus for -glucuronidase is possibly assigned to band 7q22.     

Evaluation of antibody inhibition assays of melanoma antigens in sera to monitor tumor growth in melanoma patients

Summary It was reported previously that melanoma leukocyte-dependent antibody (LDA) in the sera of melanoma patients was inhibited by small-molecular-weight (small-mol.-wt.) glycoproteins which were similar to cell surface antigens identified in cell membrane extracts of melanoma cells. The present study was to determine whether measurement of the levels of these factors in sera may be a useful monitor of tumor growth in melanoma patients. Small-mol.-wt. fractions were obtained by gel filtration or membrane chromatography of acidified sera and tested for their ability to inhibit LDA in ⁵¹Cr release cytotoxic assays. A panel of LDA was used, consisting of three antisera from melanoma patients, which appeared relatively specific for melanoma, and three non-melanoma antisera against carcinoembryonic antigen, ₂ microglobulin, and fetal antigens. The results showed that in patients with melanoma, approximately 70% had melanoma LDA-inhibitory activity detected in the small-mol.-wt. fractions of their sera when these were tested against the panel of melanoma LDA. The specificity of the inhibitory activity for melanoma LDA was shown by failure of the serum fractions to inhibit non-melanoma LDA and by absence of inhibitory activity in equivalent serum fractions from non-melanoma carcinoma patients for melanoma LDA. The levels of melanoma LDA-inhibitory activity in the serum fractions appeared to correlate with tumor growth, as shown by clearance of the inhibitory activity after surgical removal of melanoma and reappearance in the serum of patients who subsequently developed recurrent melanoma. The 30% false-negative rate indicated that the assays could not be used to reliably exclude melanoma, but the close correlation with tumor growth and the low number of false-positive results suggested that in 70% of patients detection of these small-mol.-wt. antigens would be of value to detect recurrence from melanoma and to monitor the effectiveness of therapy.     

Correlative immunocytochemical and electron microscopic studies: Identification of (Entero)glucagon-somatostatin- and pancreatic polypeptide-like-containing cells in the human colon

Summary Correlative immunocytochemical and electron microscopic studies, using the semi thin-thin technic, were performed to identify the (entero) glucagon, somatostatin and pancreatic polypeptide-like immunoreactive cells of the human colonic mucosa. Mean granule diameter for each cell type was estimated according to two methods and histograms showing the granule size distribution were constructed. A total of 139 immunostained cells identified at the ultrastructural level were analyzed. Mean granule diameter for (entero)glucagon-containing cells was 318±11 nm but a reduction of granule size with age was noteworthy: granules were larger in the fetus (mean diameter 350±15) than in adults (mean diameter 310±10 nm). Somatostatin-containing cells, very rare in adults, were present in the fetal distal colon. Their general mean granule diameter was 354±18 nm but many cells had a mean granule diameter of more than 400 nm. A pancreatic polypeptidelike immunoreactivity was found only in (entero)glucagon-containing cells, pointing out the possible occurrence of both peptides (or of similar sequences) in the same cells. Previous ultrastructural studies dealing with a tentative classification of the human colonic endocrine cells were compared with the present data.This work was supported by the Institut National de la Santé et de la Recherche Médicale (INSERM).