The effect of iron chelate fertilization of poplar upon CO2-uptake,leaf size,and content of leaf pigments and iron

Summary Potted poplars (strainsmarilandica, serotina andFlachslanden ofPopulus euramericana) which developed iron-deficiency symptoms (chlorosis of upper leaves, winter die-back of leader, flushing of lateral buds) were treated with a soil application of iron chelate to study the effect of iron nutrition upon CO₂-uptake, iron and pigment content of leaves, and leaf size of a tree species. Foliar content of each iron, chlorophyll, -carotene, lutein, and violaxanthin was significantly increased by the treatment. Chlorophyll b proved to be particularly sensitive to iron supply and the Q^a/b was also significantly altered.CO₂-uptake increased in fertilized and non-fertilized leaves with increasing light up to 40,000 Lux, but fertilized leaves assimilated more CO₂ than non-fertilized leaves, especially at light intensities from 5,000 Lux upwards. The assimilatory number was decreased by the iron application since larger amounts of chlorophyll were present in fertilized leaves. If CO₂-uptake was based upon an area unit basis the fertilizer effect became distinct even at 500 Lux. Thus CO₂-uptake is a quick, valuable measure of fertilizer responses.In severe cases, iron deficiency also affects leaf size and thus indirectly reduces photosynthetic activity. A chelate application during the growing season will not affect the size of leaves already formed but may considerably increase the size of leaves formed subsequent to the treatment.     

ESR-Untersuchungen an bestrahlten schwefelhaltigen und schwefelfreien Pyridoxinderivaten

Zusammenfassung Sowohl nach UV-Bestrahlung (254 nm) als auch nach Röntgenbestrahlung bei 20 °C ergeben sich für Pyridoxin und einige schwefelhaltige Pyridoxinderivate gleiche Radikalzustände. Wahrscheinlich befindet sich ein unpaares Elektron in der Methylgruppe der Stellung 4 oder 5. Bei den Derivaten, die den Schwefel in Form des Sulfhydryls enthalten, findet eine Radikalwanderung zum Schwefel statt. Dabei wird der Radikalzustand am Schwefel des 4-Mercaptopyridoxins schneller gebildet als im Falle des 5-Mercaptopyridoxins. Die Disulfidbindung des Pyrithioxins ist gegenüber den Sulfhydrylbindungen der Mercaptopyridoxine stabiler. Ist der Schwefel in Form eines Thioäthers vorhanden (4,5-Methylensulfidpvridoxin), so erhält man ein Radikal vom Alkyltyp, ohne daß anschließend eine Radikalwanderung zum Schwefel auftritt. Die ESR-Untersuchungen zeigen darüber hinaus, daß die Bildung und das Zeitverhalten der Radikale nicht nur von ihrer unmittelbaren Umgebung, sondern auch von der ganzen Struktur des Moleküls abhängig sind.Herrn Prof. Dr. KurtSommermeyer zum 60. Geburtstag gewidmet.     

MHC class II invariant chains in antigen processing and presentation

Most protein antigens cannot elicit a T-cell response unless they are processed to peptides, which are then presented to T lymphocytes by surface MHC class II molecules. Recent evidence supports an essential role of the invariant chain associated with class II MHC polypeptides in antigen processing.     

The Na+,K+,2Cl- -cotransport system in HeLa cells and HeLa cell mutants exhibiting an altered efflux pathway

We have investigated the characteristics of a transport system in HeLa cells, which turned out to be very similar to a previously described Na+, K+, 2Cl- -cotransport system. For further understanding about the physiological role of the cotransporter, we have mutagenized HeLa cells and selected progeny cells for growth in low potassium (0.2 mM) medium. The selected HeLa cells (LK1) exhibited alterations in the Na+,K+,2Cl- -cotransport system. LK1 cells showed a remarkable reduction of 86Rb+ efflux via the cotransporter when compared to the parental HeLa cells. In contrast, bumetanide-sensitive potassium influx, measured by 86Rb+ uptake, was increased in the LK1 cells (increase in Vmax). Km values of the cotransporter in HeLa cells and LK1 mutants revealed similar properties for 86Rb+ and 22Na+ uptake. In addition, (3H)-bumetanide binding studies were carried out on intact HeLa cells; 1.7 pmol/mg protein (3H)-bumetanide was specifically bound to HeLa parental cells, which could be calculated to a number of 103,000 binding sites/cell. LK1 cells present, 1.44 pmol/mg protein, specifically bound (3H)-bumetanide and, respectively, 137,000 binding sites/cell. The LK1 cells also exhibited an increase in the number of (3H)-ouabain binding sites as well as an increase in the activity of the Na+,K+-ATPase, expressed as a function of ouabain-sensitive 86Rb+ uptake. Furthermore, LK1 cells were different in the concentrations of intracellular Na+ (increases) and K+ (decreases) when compared to the HeLa parental cells. When grown in low K+ medium (0.2 mM K+), protein content and cell volume were increased in the LK1 cells, while the DNA content was not significantly different between both cell lines.     

Development of chicken embryos in a pulsed magnetic field

Six independent experiments of common design were performed in laboratories in Canada, Spain, Sweden, and the United States of America. Fertilized eggs of domestic chickens were incubated as controls or in a pulsed magnetic field (PMF); embryos were then examined for developmental anomalies. Identical equipment in each laboratory consisted of two incubators, each containing a Helmholtz coil and electronic devices to develop, control, and monitor the pulsed field and to monitor temperature, relative humidity, and vibrations. A unipolar, pulsed, magnetic field (500-microseconds pulse duration, 100 pulses per s, 1-microT peak density, and 2-microseconds rise and fall time) was applied to experimental eggs during 48 h of incubation. In each laboratory, ten eggs were simultaneously sham exposed in a control incubator (pulse generator not activated) while the PMF was applied to ten eggs in the other incubator. The procedure was repeated ten times in each laboratory, and incubators were alternately used as a control device or as an active source of the PMF. After a 48-h exposure, the eggs were evaluated for fertility. All embryos were then assayed in the blind for development, morphology, and stage of maturity. In five of six laboratories, more exposed embryos exhibited structural anomalies than did controls, although putatively significant differences were observed in only two laboratories (two-tailed Ps of .03 and less than .001), and the significance of the difference in a third laboratory was only marginal (two-tailed P = .08). When the data from all six laboratories are pooled, the difference in incidence of abnormalities in PMF-exposed embryos (approximately 25 percent) and that of controls (approximately 19 percent), although small, is highly significant, as is the interaction between incidence of abnormalities and laboratory site (both Ps less than .001). The factor or factors responsible for the marked variability of inter-laboratory differences are unknown.