Ultrastructure d'une cyanophycée aérienne calcifiée cavernicole:Scytonema julianum (Frank) Richter (Hormogonophycideae,Nostocales, Scytonemataceae)

The ultrastructure of the atmophytic lime-encrusted filamentous blue-green algaScytonema julianum (Frank) Richter which grows in caves, is studied here for the first time. The cytology of this organism is compared with that of another filamentous and lime-encrusted cyanophycea,Geitleria calcarea Friedmann, which grows in the same biotope. The authors also discuss the nomenclature of this quite rare species.

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Ultrastructure d'une cyanophycée aérienne calcifiée cavernicole:Scytonema julianum (Frank) Richter (Hormogonophycideae, Nostocales, Scytonemataceae)

     

Synaptic membranes from Torpedo marmorata electric organ. 1. Separation and analysis of nicotinic acetylcholine receptor- and acetylcholinesterase-containing membrane vesicles using aqueous two-phase systems

Two-phase systems consisting of water, dextran and poly(ethylene glycol) have been used for partition of membranes obtained from Torpedo marmorata electric organ. The partition behaviour of the membranes could be adjusted by using a polymer with covalently-bound charged groups. By using this method, the membranes were divided into several fractions which were analyzed for nicotinic acetylcholine receptor and acetylcholinesterase content. It was found that nicotinic receptor-enriched membranes were separated from those containing esterase in a single partition step. Receptor-enriched membranes obtained by gradient centrifugation could be further separated into two receptor fractions by the two-phase technique. The results also reveal at least two types of acetylcholinesterase-rich membranes.     

Sekundäre Weichbodenbewohner unter den Cirripediern

For various reasons, but mainly because of reproductional constraints, cirriped arthropods have evolved less secondary soft bottom dwellers than other sessile groups of organisms. Presented examples are (1) a modern balanid that lives commensally on a small burrowing bivalve and (2) the Cretaceoous /EoceneWaiparaconus, wich is re-established as a lepadomorph whose peduncle has become transformed into a solid, horn shaped anchoring device.     

Characteristics of human chondrocyte cultures in completely defined medium

Summary Chondrocytes derived from normal human adult articular cartilage were established and maintained for over 5 months in a completely defined medium without the addition of serum or any other growth factors. At the end of 5 months, these cells were still metabolically active. The cells incorporated [³H]thymidine into DNA, incorporated [³⁵S]sulfate into proteoglycans, and exhibited lysosomal enzyme activities. The³⁵S-labeled proteoglycans isolated from the culture medium had elution profiles on high pressure liquid chromatography (HPCL) similar to those observed from proteoglycans from other mammalian sources. This self-contained growth competence may reflect a need produced by the unusual avascular and alymphatic character of articular cartilage. This research was supported, in part, by Grant AM22057 from the National Institutes of Health, Bethesda, MD.     

Effect of ageing on enzymes of phenylpropanoid metabolism in Solanum tuberosum discs

-Separation of cell fractions or cell organelles of potato tuber by differential centrifugation and by sucrose density gradient centrifugation showed that, in dormant tissue, nearly all the activity of shikimate and prephenate dehydrogenases, phenylalanine ammonia lyase, cinnamate-4-hydroxylase and an O-methyltransferase for caffeate was in the soluble fraction. All these enzymes increased in activity in slices aged in light for 18 hr. In contrast to the other enzymes, cinnamate hydroxylase becomes associated with the microsomal fraction in aged discs.     

Pitfalls in the Assay of Cyclic AMP-Dependent Protein Kinase Activity in Microsacs from Torpedo marmorata

Endogenous phosphorylation of the nicotinic acetylcholine receptor (nAChR) in microsacs from Torpedo marmorata was found to be affected by several reagents commonly used in the preparation of cyclic AMP (cAMP)-dependent protein kinases and in its activity determination. The presence of a Na+,K+-ATPase inhibitor is essential to avoid a rapid depletion of ATP, even when a membrane fraction highly enriched in the nAChR is used. The presence of the thiol reducing agent dithiothreitol was found to abolish the cAMP dependence of nAChR phosphorylation, whereas the less potent reagent 2-mercaptoethanol did not affect the assay. Concentrations in the millimolar range of the chelators EDTA and EGTA were found to inhibit nAChR phosphorylation effectively. This inhibition was not due to a withdrawal of Ca2+ by the chelators, but rather to a reversible inhibition by the Mg2+ complexes. These observations may explain some of the discrepancies found in the literature concerning endogenous and exogenous nAChR phosphorylation.     

On selective partial sterility as an explanation of the behavior of the double-throwing stock and the Petunia

Ohne Zusammenfassung

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On selective partial sterility as an explanation of the behavior of the double-throwing stock and the Petunia