Survival Rate and Enzyme Activities ofLactobacillus acidophilusFollowing Frozen Storage

The ability of two strains of Lactobacillus acidophilus, CRL 640 and CRL 800, to survive and retain their biological activities under frozen storage was determined. Freezing and thawing, as well as frozen storage, damaged the cell membrane, rendering the microorganisms sensitive to sodium chloride and bile salts. Both lactic acid production and proteolytic activity were depressed after 21 days at -20 degreesC, whereas beta-galactosidase activity per cell unit was increased. Cell injury was partially overcome after repair in a salt-rich medium. Copyright 1998 Academic Press.     

Novel regulatory mechanisms for generation of the soluble leptin receptor: implications for leptin action

Background

The adipokine leptin realizes signal transduction via four different membrane-anchored leptin receptor (Ob-R) isoforms in humans. However, the amount of functionally active Ob-R is affected by constitutive shedding of the extracellular domain via a so far unknown mechanism. The product of the cleavage process the so-called soluble leptin receptor (sOb-R) is the main binding protein for leptin in human blood and modulates its bioavailability. sOb-R levels are differentially regulated in metabolic disorders like type 1 diabetes mellitus or obesity and can, therefore, enhance or reduce leptin sensitivity.

Methodology/Principal Findings

To describe mechanisms of Ob-R cleavage and to investigate the functional significance of differential sOb-R levels we established a model of HEK293 cells transiently transfected with different human Ob-R isoforms. Using siRNA knockdown experiments we identified ADAM10 (A Disintegrin And Metalloproteinase 10) as a major protease for constitutive and activated Ob-R cleavage. Additionally, the induction of lipotoxicity and apoptosis led to enhanced shedding shown by increased levels of the soluble leptin receptor (sOb-R) in cell supernatants. Conversely, high leptin concentrations and ER stress reduced sOb-R levels. Decreased amounts of sOb-R due to ER stress were accompanied by impaired leptin signaling and reduced leptin binding.

Conclusions

Lipotoxicity and apoptosis increased Ob-R cleavage via ADAM10-dependent mechanisms. In contrast high leptin levels and ER stress led to reduced sOb-R levels. While increased sOb-R concentrations seem to directly block leptin action, reduced amounts of sOb-R may reflect decreased membrane expression of Ob-R. These findings could explain changes of leptin sensitivity which are associated with variations of serum sOb-R levels in metabolic diseases.     

Embryogenic callus induction and plant regeneration media for bentgrasses and annual bluegrass

Summary Embryogenic callus induction and plant regeneration systems have long been established for creeping bentgrass (Agrostis palustris Huds.), but little research has been reported on optimal medium for embryogenic callus induction and plant regeneration in velvet bentgrass (Agrostis canina L.), colonial bentgrass (Agrostis capillaries L.), and annual bluegrass (Poa annua L.). The present study compared 14 callus induction media and eight regeneration media for their efficacies on embryogenic callus induction and plant regeneration in these four species. The embryogenic callus initiation media contained the Murashige and Skoog inorganic salts and vitamins supplemented with 2,4-dichlorophenoxyacetic acid or 3,6-dichloro-anisic acid and 6-benzyladenine. l-Proline or casein hydrolyzate was included in some media to stimulate embryogenic callus formation and plant regeneration. The frequencies of embryogenic callus formation ranged from 0% to 38% and exhibited medium differences within each of the four species. Callus induction media, plant regeneration media, and genotypes affected plant regeneration rates, which varied between 0% and 100%. The embryogenic callus induced on Murashige and Skoog medium supplemented with 500 mgl⁻¹ casein hydrolyzate, 6.63 mg l⁻¹ (30 μM) 3,6-dichloro-anisic acid and 0.5–2.0 mg l⁻¹ (2–9 μM) 6-benzyladenine had much higher regeneration rates than those formed on other callus induction media. Embryogenic callus of annual bluegrass had higher regeneration rates than those of bentgrass species. MSA2D, a media containing 2 mgl⁻¹ (8 μM) 2,4-dichlorophenoxyacetic acid, 100 mgl⁻¹ myo-inositol, and 150 mgl⁻¹ asparagine, was effective in promoting embryogenic callus formation in creeping bentgrass but not in colonial and velvet bentgrasses and annual bluegrass.     

Physiologische Wirkungen kleinster Saugkräfte

Ohne ZusammenfassungMit 2 TextabbildungenMit Unterstützung der Deutschen Forschungsgemeinschaft.     

Saugkraft und Wassernachleitung im Boden als physiologische Faktoren

Ohne ZusammenfassungMit 19 Textabbildungen.Für die Anregung und Förderung dieser Arbeit, die im Rahmen meiner Dissertation entstanden ist, habe ich Herrn Professor Dr.O. Stocker zu danken. Die Deutsche Forschungsgemeinschaft gewährte finanzielle Unterstützung.     

Licht- und ultraviolettmikroskopische Beobachtungen an Schließzellen nach ihrer Reaktion auf verschiedene Umweltbedingungen1

• 1 . Zellkerne, Chloroplasten und Sphärosomen der Schließzellen lassen sich in der Regel schon im sichtbaren Licht mit dem DIK-Verfahren sehr gut darstellen
• 2 . Wichtige Strukturunterschiede an Zellkern, Chloroplasten und Vakuolen wurden in geöffneten und geschlossenen lebenden Schließzellen mit dem UV-Mikroskop (ZEISS) gefunden
• 3 . Die UV-Absorption der Flavonoide bzw. phenolischen Pflanzeninhaltsstoffe in geschlossenen Stomata ist hoch, die der geöffneten gering (Abbau?). Wegen der großen Menge an Flavonoiden im Zellsaft der Freilandpflanzen wird eine Veränderung ihres Absorptionsvermögens nur schwer nachweisbar sein
• 4 . Hohe Temperaturen (bis 41 °C) oder Lagerung der Epidermen in Paraffinöl führen nach etwa 24 Stunden zu einem Verschwinden der Flavonoidabsorption und zu einer Schädigung der Stomata
• 5 . Wassermangel durch Welken des Blattes führt zu einer reversiblen Konvexplasmolyse der Schließzellen. Die Flavonoidabsorption bleibt dabei weitgehend erhalten

     

Comparison of the Respiratory Metabolism of Plantago lanceolata L. and Plantago major L.

Bryce, J. H. and ap Rees, T. 1985. Comparison of the respiratorymetabolism of Plantago lanceolata L. and Plantago major L.—J.exp. Bot. 36 1559–1565. The aim of this work was to discover if the respiratory metabolismof the roots of Plantago lanceolata L. differed from that ofthe roots of Plantago major L. Measurements of oxygen uptakeand dry weight of excised root systems during growth of seedlingsprovided evidence that the two species differed in the amountof respiration needed to support a given increase in dry weight.Excised root systems were given a 6-h pulse in [U-¹⁴C]sucrosefollowed by a 16.5-h chase in sucrose. The detailed distributionof ¹⁴C amongst the major components of the roots at the endof the pulse and the chase revealed no significant differencebetween the two species. Patterns of ¹⁴CO₂ production from [1-¹⁴C],[2-¹⁴C], [3,4-¹⁴C], and [6-¹⁴C]glucose of excised root systemsfrom plants of three ages were similar for the two species.It is suggested that there is no conclusive evidence for anysignificant inherent difference in the respiratory metabolismof the roots of the two species. Key words: ¹⁴C sugar metabolism, respiration, roots, Plantago