The differentiating agent, retinoic acid, causes an early inhibition of inositol lipid-specific phospholipase C activity in HL-60 cells

Retinoic acid, a derivative of vitamin A, is shown to inhibit the levels of inositol phosphates and diacylglycerol by 25-30% when added to intact HL-60 cells at concentrations which induce differentiation. The onset of inhibition occurs after 10 min and reaches a maximum at 45 min. To study the mechanism and the site of action of retinoic acid, the activity of the phosphatidylinositol bisphosphate-specific phospholipase C was studied in cells permeabilized with streptolysin O and in membrane preparations. Phospholipase C activity was stimulated either via the guanine nucleotide regulatory protein (G-protein) or directly by Ca2+. Retinoic acid treatment, in a time- and concentration-dependent manner, led to a decrease in phospholipase C activity when stimulated with either GTP gamma S or NaF, both of which activate the enzyme via the G-protein. By contrast, it had no effect on the enzyme activity when stimulated with Ca2+ alone. This indicates that retinoic acid interferes with the coupling of the G-protein and phospholipase C. A relationship between the inhibition of phospholipase C activity and the induction of differentiation by retinoic acid was investigated. Only a small inhibition of GTP gamma S-stimulated phospholipase C activity was observed when an analogue of retinoic acid, etretine or Ro10-1670, with low differentiating activity, was used. Moreover, no inhibition of the GTP gamma S-stimulated phospholipase C activity was observed in an HL-60 sub-line resistant to retinoic acid. These results suggest that phospholipase C inhibition is an important step in the induction of differentiation.     

A Mouse Chromosome-Specific YAC Probe Collection forin SituHybridization

To facilitate the identification of mouse metaphase chromosomes by fluorescencein situhybridization (FISH), a complete collection of mouse chromosome-specific markers has been established. Yeast artificial chromosome libraries were screened by polymerase chain reaction using primers for known loci. DNAs from positive clones were then tested by FISH. One probe per chromosome was selected on the basis of high specificity (nonchimerism) and strong fluorescence.     

Proteasomes (prosomes) inhibit the translation of Tobacco mosaic virus RNA by preventing the formation of initiation complexes

Proteasomes (prosomes) are large multiprotein complexes. They are involved in protein degradation of ubiquitin-conjugated proteins and in the generation of MHC class I peptides. We gave further evidence that they interfere within vitro protein synthesis. Proteasomes inhibit the translation of Tobacco mosaic virus RNA. Analysis of cell-free systems by sucrose gradient centrifugation revealted that they prevent the formation of 80S initiation complexes but not the early phase of initiation.     

A tripartite culture system for endomycorrhizal inoculation of micropropagated strawberry plantlets in vitro

The objective of the current investigation was to develop a reliable method to obtain vesicular arbuscular mycorrhizae (VAM) in micropropagated plantlets and to determine their influence on growth. An in vitro system for culturing the VA mycorrhizal fungus Glomus intraradices with Ri T-DNA-transformed carrot roots or nontransformed tomato roots was used in this study as a potential active source of inoculum for the colonization of micropropagated plantlets. After root induction, micropropagated plantlets grown on cellulose plugs (sorbarod) were placed in contact with the primary mycorrhizae in growth chambers enriched with 5000 ppm CO₂ and fed with a minimal medium. After 20 days of tripartite culture, all plantlets placed in contact with the primary symbiosis were colonized by the VAM fungus. As inoculum source, 30-day-old VA mycorrhizal transformed carrot roots had a substantially higher infection potential than 5-, 10-or 20-day-old VAM. Colonized plantlets had more extensive root systems and better shoot growth than control plants. The VAM symbiosis reduced the plantlet osmotic potential. This response may be a useful pre-adaptation for plantlets during transfer to the acclimatization stage.     

Preparation of α- and β-dienyl glycosides used as dienes in aqueous Diels-Alder reactions. Influence of the carbohydrate moiety on the thermodynamics of the reaction

A series of 1,3-butadienyl glycosides (mono- and di-saccharides) have been prepared and the kinetics of their Diels-Alder reaction with buten-2-one in water have been studied. The activation parameters for these aqueous cycloadditions provide clues for the hydration structure of such glyco-organic compounds.     

Qualité des eaux en milieu estuarien: Suivi annuel de critères physiques et chimiques dans les eaux de l'estuaire de la Loire

Chemical composition and physical parameters of waters from the Loire estuary were examined in 1981–1982 in order to assess water quality. It appears that riverflow is of first importance on suspended matter load, dissolved nutrient concentrations and oxygenation. The annual hydrological cycle is made of two periods. During the first one low riverflow, low nutrient concentrations, high suspended matter load and oxygen depletion are noticed. During the second one higher riverflows occur accompanied with increasing nutrient concentrations, decreasing turbidity and restoration of dissolved oxygen. Results indicate that annual inputs of dissolved nutrients attain 60 000 t a^–1 for nitrogen, 2 400 t a^–1 for phosphorus and 100 000 t a^–1 for silica. It is suggested that the high suspended matter loading (¹ million t a^–1) is a significant factor disturbing oxygenation and by the way limiting water quality within the estuary.

     

Proton gradient across membranes of lecithin vesicles as measured by 31P-NMR: Asymmetrical behaviour of internal and external layers

The ionization of phosphate ions trapped inside sonicated egg yolk lecithin vesicles was determined as a function of internal pH values using a ³¹PNMR. The chemical shift of the internal phosphate signal reflects the intravesicular pH perfectly. At 30°C, protons once inside vesicles (pH int < pH ext) cannot get across the inner layer even under a pH gradient up to five units. On the other hand, when pH (int) >pH(ext), the results suggest that protons may cross the outer but not the inner layer and interact with the internal phosphate ions.