The transepithelial potential difference in the gills of the fiddler crab,Uca tangeri: Influence of some inhibitors

Summary Euryhaline Crustacea living in dilute media, counterbalance the salt loss by active absorption of NaCl across the gill epithelium. To investigate the mechanisms involved in salt absorption, transeptithelial potential difference (PD_te) was measured in isolated, perfused gills of the fiddler crab,Uca tangeri. The influence of some specific inhibitors of epithelial ion transport on the PD_te was tested.With symmetrical conditions on both sides of the epithelium, the posterior gills ofUca tangeri showed a spontaneous PD_te of +5 to +10 mV, that is an active transport potential which was positive on the bath side as referred to the hemolymph side. This potential decreased considerably after application of KCN or 2,4-dinitrophenol (DNP) to the perfusion saline.Omission of K⁺ from the perfusion saline or addition of ouabain led to a reversible drop of the PD_te, suggesting that the absorption of Na⁺ and also of Cl^– is driven by the (Na⁺+K⁺)ATPase located in the basolateral membrane of the epithelial cells.Perfusion of the hemolymph space with saline containing diphenylamine-2-carboxylate (DPC) or the loop diuretic furosemide resulted in a decrease of the PD_te.After application of amiloride to the bath saline the PD_te increased. Half-maximum response to amiloride was reached at a concentration of about 10^–5 mol·l^–1. This suggests that one of the Na⁺ pathways across the apical membrane may consist of Na⁺ channels.Abbreviations PD _te transepithelial potential difference - DPC diphenylamine-2-carboxylate - R _ps resistance of perfusate shunt - R _te transepithelial resistance - R _in input resistance - DNP 2,4-dinitrophenol Parts of this study have been reported at the 1st Congress of Comparative Physiology and Biochemistry, Liège 1984, and at the Vth European Colloquium on Renal Physiology, Frankfurt, 1985     

Human hepatic triglyceride lipase: cDNA cloning, amino acid sequence and expression in a cultured cell line

By immunoscreening of a human cDNA expression library and hybridization of colonies, four partially overlapping cDNA clones of human hepatic triglyceride lipase (HTGL) mRNA were isolated. The clones included the complete coding sequence, the 3'- and at least part of the 5'-untranslated region. The length of the composite HTGL cDNA segment (1.7 kb) was consistent with the size of the mRNA identified in an established human hepatoma cell line. DNA-sequence analysis of cDNAs of partially unspliced mRNAs, and of cloned genomic DNA indicated that the HTGL coding sequence comprises at least six exons. As predicted from the cDNA, the unprocessed HTGL protein has a molecular weight of 56, three potential glycosylation sites, and a signal peptide of 23 amino acids. Sequence comparison with cDNA of other lipases, including rat hepatic lipase, revealed 30%-75% protein-sequence homology. The data establish that HTGL is a secretory protein produced in the hepatocyte, and that its synthesis can be continued in permanent cell lines of hepatoma origin. Our studies also showed that HTGL is another member of a lipase gene family which has interfacial binding sites and possibly other functional domains in common.     

A monozygotic twin pair with Rett syndrome

Summary A five-year-old, monozygotic, Turkish female twin pair with Rett syndrome is described. The twins are almost completely concordant in all clinical signs. This observation suggests a genetic cause of Rett syndrome.     

Detection of Sap-Transmissible Viruses by ELISA in Tissue-Propagated Plants of Red Raspberry during in vitro Culture

Apple mosaic virus and raspberry bushy dwarf virus were detected by ELISA in plantlets of red raspberry still growing in vitro. The plantlets were derived from explants which were excised from plants infected by either of the viruses mentioned. Detection by ELISA of prune dwarf virus in 4-month-old in vitro cultures of sour cherry was reported earlier. Thus, application of ELISA to tissue cultured plants in vitro seems to be an appropriate method for early detection of virus-infected plant cultures.     

High intensity and blue light regulated expression of chimeric chalcone synthase genes in transgenic Arabidopsis thaliana plants

Summary To establish a genetic system for dissection of light-mediated signal transduction in plants, we analyzed the light wavelengths and promoter sequences responsible for the light-induced expression of the Arabidopsis thaliana chalcone synthase (CHS) promoter fused to the -glucuronidase (GUS) marker gene. Transgenic A. thaliana lines carrying 1975, 523, 186, and 17 by of the CHS promoter fused to the GUS gene were generated, and the expression of these chimeric genes was monitored in response to high intensity light in mature plants and to different wavelengths of light in seedlings. Fusion constructs containing 1975 and 523 by of CHS promoter sequence behaved identically to the endogenous CHS gene under all conditions. Expression of these constructs was induced specifically in response to high intensity white light and blue light. The response to blue light was seen in the presence of the P_fr form of phytochrome. Fusion constructs containing 186 by of promoter sequence showed reduced basal levels of expression and only weak stimulation by blue light but were induced significantly by high intensity white light. These analyses showed that the expression of the A. thaliana CHS gene is responsive to a specific blue light receptor and that sequences between — 523 and — 186 by are required for optimal basal and blue light-induced expression of this gene. The experiments lay the foundation for a simple genetic screen for light response mutants.     

Stearidonic acid (18:4ω3) in Primula florindae

Stearidonic acid (18:4ω3), which is reported to be of rare occurrence in the plant kingdom and which is of considerable dietary and pharmaceutical interest has been found in three closely related Primula species. It occurs, together with γ-linolenic acid (3–4% of the seed oil total fatty acids), in significant percentages in Primula florindae (11%), P. sikkimensis (14%) and P. alpicola (14%). 18:4(ω3 may also be of chemotaxonomic interest in the genus Primula, as high levels may be typical for section Sikkimensis. The only commercial plant source of stearidonic acid known so far is the seed oil of Ribes nigrum.     

Indolderivate im Apfel

Zusammenfassung Zur Identifizierung der Streckungswuchsstoffe in Apfelgeweben wurden Extrakte aus vegetativen und reproduktiven Organen in verschiedenen Entwicklungsstadien chromatographiert und mit Hilfe des Weizen-Koleoptilzylinder-Tests, verschiedener Farbreagentien und synthetischer Vergleichssubstanzen auf ihre Wuchsstoffwirkung und ihren Gehalt an Indolderivaten geprüft. Alle untersuchten Gewebe ergaben im biologischen Test dieselben Wuchsstoffe, allerdings mit erheblichen quantitativen Unterschieden.In der sauren Fraktion von Ätherextrakten aus dem Fruchtfleisch verschiedener Apfelsorten ließen sich Malonyltryptophan, Indol-3-carbonsäure, 2-Hydroxy-indol-3-essigsäure, Indol-3-essigsäure, Indol-3-aldehyd (vor allem in reifen Früchten) und Indol-3-essigsäure-äthylester (in unreifen Früchten) identifizieren. In Gegenwart von IES trat häufig auch Indol-3-acetamid auf; dieses, die Indol-3-essigsäure und 2-Hydroxy-indol-3-essigsäure und der Indol-3-essigsäure-äthylester zeigten im Weizen-Koleoptilzylinder-Test Wuchsstoffwirkung.Nach Hydrolyse des mit Äther extrahierten Materials fanden sich neben einer größeren Anzahl unbekannter Substanzen, die im Farb-Test Indolreaktionen ergaben, drei weitere, im biologischen Test aktive Indolderivate, von denen das eine als Indol-3-acetylasparaginsäure identifiziert werden konnte; die anderen beiden sind möglicherweise ebenfalls Verbindungen der IES mit Aminosäuren.Im Weizen-Koleoptilzylinder-Test konnte eine Überlagerung der Indolderivate mit unbekannten, ebenfalls aktiven Substanzen nicht ausgeschlossen werden.Mit 3 Textabbildungen     

Amplification of small signals by voltage-gated sodium channels in drone photoreceptors

Summary Photoreceptor cells of the drone,Apismellifera , have a voltage-gated Na⁺ membrane conductance that can be blocked by tetrodotoxin (TTX) and generates an action potential on abrupt depolarization: an action potential is triggered by the rising phase of a receptor potential evoked by an intense light flash (Autrum and von Zwehl 1964; Baumann 1968). We measured the intracellular voltage response to a small (9%), brief (30 ms) decrease in light intensity from a background, and found that its amplitude was decreased by 1M TTX. The response amplitude was maximal when the background intensity depolarized the cell to –38 mV. With intensities depolarizing the cell membrane to –45 to –33 mV the average response amplitude was decreased by TTX from 1.2mV to 0.5mV. TTX is also known to decrease the voltage noise during steady illumination (Ferraro et al. 1983) but, despite this, the ratio of peak-to-peak signal to noise was, on average, decreased by TTX. The results suggest that drone photoreceptors use voltage-gated Na⁺ channels for graded amplification of responses to small, rapid changes in light intensity.Abbreviations TTX tetrodotoxin - V _i intracellular potential with respect to the bath - V _o extracellular potential - V _m,V _i-V _o approximate transmembrane potential - S amplitude of the voltage response to an 8.9% decrease in light intensity - N voltage noise, usually measured as root mean square voltage deviation as described in Methods     

The effect of endogenous and externally supplied nitrate on nitrate uptake and reduction in sugarbeet seedlings

The pericarp of the dormant sugarbeet fruit acts as a storage reservoir for nitrate, ammonium and -amino-N. These N-reserves enable an autonomous development of the seedling for 8–10 d after imbibition. The nitrate content of the seed (1% of the whole fruit) probably induces nitrate-reductase activity in the embryo enclosed in the pericarp. Nitrate that leaks out of the pericarp is reabsorbed by the emerging radicle. Seedlings germinated from seeds (pericarp was removed) without external N-supply are able to take up nitrate immediately upon exposure via a low-capacity uptake system (v_max = 0.8 mol NO ₃ ^- ·(g root FW)^–1·h^–1; K_s = 0.12 mM). We assume that this uptake system is induced by the seed nitrate (10 nmol/seed) during germination. Induction of a high-capacity nitrate-uptake system (v_max = 3.4 mol NO ₃ ^- ·(g root FW)^–1·h^–1; K_s = 0.08 mM) by externally supplied nitrate occurs after a 20-min lag and requires protein synthesis. Seedlings germinated from whole fruits absorb nitrate via a highcapacity uptake mechanism induced by the pericarp nitrate (748 nmol/pericarp) during germination. The uptake rates of the high-capacity system depend only on the actual nitrate concentration of the uptake medium and not on prior nitrate pretreatments. Nitrate deprivation results in a decline of the nitrate-uptake capacity (t_1/2 of v_max = 5 d) probably caused by the decay of carrier molecules. Small differences in K_s but significant differences in v_max indicate that the low- and high-capacity nitrate-uptake systems differ only in the number of identical carrier molecules.Abbreviations NR nitrate reductase - pFPA para-fluorophenylalanine This work was supported by a grant from Bundesministerium für Forschung und Technologie and by Kleinwanzlebener Saatzucht AG, Einbeck.