Gamma-radiolysis of N2O-saturated formate solutions. A chain reaction

In the radiolysis of aqueous formate-containing solutions a chain reaction (i, ii) proceeds in the presence of N2O. CO2-. + N2O + H2O----CO2 + N2 + .OH + OH- (i) .OH + HCO2-.----CO2-. + H2O (ii) The chain length depends on the dose rate and the N2O concentration but not on the formate concentration. Typically, G(CO2) approximately 140 molecules (100 eV)-1 is found, with an equivalent amount of N2, at a dose rate of 3 X 10(-3) Gy s-1. The rate constant for the rate-determining step in this chain reaction has been calculated at k(i) = 1600 dm3 mol-1 s-1. The possible relevance of this chain reaction in radiation biological studies is briefly discussed.     

Inside or outside? Localization of the receptor relevant to auxin-induced growth

The localization of the auxin receptor relevant to the control of elongation growth is still a matter of controversy. Auxin-induced elongation of maize coleoptile segments was measured by means of a high resolution auxanometer. When indole-3-acetic acid (IAA) was removed from the bathing solution, a rapid cessation of auxin-induced elongation was detected. This decline was delayed when the auxin efflux carrier was blocked by the phytotropins naphthylphthalamic acid (NPA) and pyrenoylbenzoic acid (PBA) or by triiodobenzoic acid (TIBA). The IAA concentration in NPA-pretreated segments was 2–3 times higher than in NPA-free controls 35 min after the removal of IAA in the bathing medium.
A similar rapid drop of growth after removal of auxin was observed for the rapidly-transported synthetic auxin, naphthaleneacetic acid (NAA). When the auxin efflux was blocked, growth induced by NAA was sustained much longer than IAA-stimulated elongation.
In comparison with NAA, the synthetic auxin 2,4-dichlorophenoxyacetic acid (2,4-D) is known to be excreted very slowly by the efflux carrier. 2,4-D-induced growth remained at a stimulated level when the auxin was washed off, even in the absence of any auxin efflux inhibitor. We conclude from these results that the presence of intracellular auxin is a necessary and sufficient condition for sustained auxin-induced elongation growth, at least for the phases during the 2 h after its application. Consequently, we postulate the existence of an intracellular auxin receptor relevant to the control of growth.     

The biosynthesis of rosmarinic acid in suspension cultures of Coleus blumei

Suspension cultures of Coleus blumei accumulate very high amounts of rosmarinic acid, an ester of caffeic acid and 3,4-dihydroxyphenyllactate, in medium with elevated sucrose concentrations. Since the synthesis of this high level of rosmarinic acid occurs in only five days of the culture period, the activities of the enzymes involved in the biosynthesis are very high. Therefore all the enzymes necessary for the formation of rosmarinic acid from the precursors phenylalanine and tyrosine could be isolated from cell cultures of Coleus blumei: phenylalanine ammonia-lyase, cinnamic acid 4-hydroxylase, hydroxycinnamoyl:CoA ligase, tyrosine aminotransferase, hydroxyphenylpyruvate reductase, rosmarinic acid synthase and two microsomal 3- and 3-hydroxylases. The main characteristics of these enzymes of the proposed biosynthetic pathway of rosmarinic acid will be described.Abbreviations DHPL 3,4-dihydroxyphenyllactate - DHPP 3,4-dihydroxyphenylpyruvate - pHPL 4-hydroxyphenyllactate - pHPP 4-hydroxyphenylpyruvate - RA rosmarinic acid     

Reproductive biology of the Purple-crowned Fairy (Heliothryx barroti, Trochilidae) — Notes on antipredator behaviour

Zusammenfassung Während brutbiologischer Untersuchungen 1988 und 1989 an 2 Nestern der Purpurkopfelfe (Heliothryx barroti) an der pazifischen Seite der Westanden Kolumbiens (200 m NN; 03°46N/77°10W) wurde beim Abfliegen vom Nest eine Verhaltensweise beobachtet, die an ein herabfallendes Blatt erinnert. Die Übereinstimmung der Gleitgeschwindigkeiten von Kolibri und Blättern deutet darauf hin, daß die Imitation fallenden Laubes durch den Vogel als Schutz vor Nesträubern dient.     

Zur ?kologie jamaikanischer Kolibriarten

Zusammenfassung Auf Jamaika brüten 4 Kolibriarten, wobei die beiden congenerischen ArtenTrochilus polytmus undTrochilus scitulus allopatrisch leben. Jede Art weist jeweils eine eindeutige Präferenz bezüglich Meereshöhe und Vegetationshöhe auf.T. polytmus undT. scitulus stimmen in diesen beiden Parametern ihrer ökologischen Nische überein. Da sich beide Arten auch gewichtsmäßig entsprechen, nehmen sie in der nektarivoren Nahrungsgemeinschaft homologe Planstellen ein.Bei den auf Jamaika untersuchten ornithophilen Blütenpflanzen wurden Zuckerkonzentrationen von 15–22% gemessen, bei einigen auch von Insekten frequentierten Pflanzenarten solche bis 44%. Der Verlauf der Nektarsekretionsrate pro Stunde in Abhängigkeit von der Tageszeit entsprach bei Pflanzen, die ausschließlich von Kolibris bestäubt wurden, dem täglichen Aktivitätsrhythmus der Kolibris. Blütenpflanzen, die sowohl von Kolibris als auch von Insekten besucht wurden, zeigten hingegen eine weitgehend konstante stündliche Nektarproduktionsrate am Tage.Artspezifisch unterschiedliche Blütenpflanzen wurden als Nahrungsquelle ausgewählt. Diese nahrungsökologische Separation ist darauf zurückzuführen, daß die Kolibriarten aufgrund ihrer Gewichtsunterschiede jeweils nur bei bestimmten ornithophilen Blütenpflanzenarten einen Nettoenergiegewinn erzielen können (z. B. Nettoenergiegewinn bei der Nahrungsaufnahme im Schwirrflug aus einer Blüte vonAsclepias currassavica vonMellisuga minima: 0.308 cal,Anthracothorax mango: — 0.661 cal).

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On the ecology of Jamaican hummingbirds

Summary On Jamaica 4 hummingbird species are resident. The congeneric speciesTrochilus polytmus andTrochilus scitulus are geographically separated (allospecies). Relative abundance depending on altitude and on height of vegetation (proportional occurence of each species in mist-netted samples s. Fig. 1,2) indicate a species-specific preference in both parameters.T. polytmus andT. scitulus correspond in both ecological parameters as well as in morphological characteristics. It is argued that both species occupy homologous niches in their range of distribution.Nectar of all studied ornithophilic plant species varied in sugar concentration from 15% to 22%. Flowering plants visited by insects and hummingbirds reached a sugar concentration in nectar of 44% (s. Tab. 1). The rate of daily nectar production per hour in plant species solely visited by hummingbirds varied according to the daily rhythm of activity of the birds (s. Fig. 3 B). Plant species visited by hummingbirds and insects showed little daily variation in nectar production per hour (s. Fig. 3 A).To gain energy benefits Jamaican hummingbirds selected flowering plants according to their weight-specific energy requirements (s. Tab. 3, 4).

     

Hypotonic stress induces E-cadherin expression in cultured human keratinocytes

Human epidermis marks the interface between internal and external environments with the major task being to maintain body hydration. Alternating exposure of skin to a dry or humid environment is likely to cause changes in the epidermal water gradient resulting in osmotic alterations of epidermal keratinocytes. The present in vitro approach studied the effect of hypotonicity on cell-cell contact. It was demonstrated that hypotonic stress applied to human epithelial cells (HaCaT, A-431) induced upregulation of E-cadherin at both, the protein and mRNA level. 5'-deletional mutants of the E-cadherin promoter identified an element ranging from -53 to +31 that conveyed strong transactivation under hypotonic stress. In order to define relevant upstream regulators members of the MAP kinase family, the epidermal growth factor receptor (EGFR) and protein kinase B/Akt (PKB/Akt) were investigated. Hypotonic conditions led to a fast activation of ERK1/2, SAPK/JNK, p38, EGFR and PKB/Akt with distinct activation patterns. Experiments using specific inhibitors showed that p38 contributes to the E-cadherin transactivation under hypotonic conditions. Further upstream, adhesion was found to be a prerequisite for E-cadherin transactivation in this model. In summary, the present study provides evidence that E-cadherin is an osmo-sensitive gene that responds to hypotonic stress. The function of this regulation may be found in morphological changes induced by cell swelling. It is likely that induction of E-cadherin contributes to the stabilization between adjacent cells in order to withstand the physical forces induced by hypotonicity.     

Nestbau und Nestanpassung an den tropischen Regenwald beiGlaucis hirsuta

Ohne Zusammenfassung     

A combined CaMKII inhibition and mineralocorticoid receptor antagonism via eplerenone inhibits functional deterioration in chronic pressure overloaded mice

In the diseased and remodelled heart, increased activity and expression of Ca^2+/calmodulin‐dependent protein kinase II (CaMKII), an excess of fibrosis, and a decreased electrical coupling and cellular excitability leads to disturbed calcium homeostasis and tissue integrity. This subsequently leads to increased arrhythmia vulnerability and contractile dysfunction. Here, we investigated the combination of CaMKII inhibition (using genetically modified mice expressing the autocamtide‐3‐related‐peptide (AC3I)) together with eplerenone treatment (AC3I‐Epler) to prevent electrophysiological remodelling, fibrosis and subsequent functional deterioration in a mouse model of chronic pressure overload. We compared AC3I‐Epler mice with mice only subjected to mineralocorticoid receptor (MR) antagonism (WT‐Epler) and mice with only CaMKII inhibition (AC3I‐No). Our data show that a combined CaMKII inhibition together with MR antagonism mitigates contractile deterioration as was manifested by a preservation of ejection fraction, fractional shortening, global longitudinal strain, peak strain and contractile synchronicity. Furthermore, patchy fibrosis formation was reduced, potentially via inhibition of pro‐fibrotic TGF‐β/SMAD3 signalling, which related to a better global contractile performance and a slightly depressed incidence of arrhythmias. Furthermore, the level of patchy fibrosis appeared significantly correlated to eplerenone dose. The addition of eplerenone to CaMKII inhibition potentiates the effects of CaMKII inhibition on pro‐fibrotic pathways. As a result of the applied strategy, limiting patchy fibrosis adheres to a higher synchronicity of contraction and an overall better contractile performance which fits with a tempered arrhythmogenesis.