Über den Einfluß der Vorbelichtung auf die anschließende Phosphorylierung im Dunkeln bei einzelligen Grünalgen (Ankistrodesmus braunii)

Zusammenfassung Wird einzelligen Algen (Ankistrodesmus braunii) nach Vorbelichtung in anschließender Dunkelheit ³²P-markiertes Phosphat geboten, so tritt gegenüber Dauerdunkel eine erhebliche Förderung der ³²P-Einlagerung auf. Die nach Vorbelichtung bestimmte Markierung der aufgetrennten Phosphatfraktionen ähnelt sehr derjenigen im Dauerlicht. Die erhöhte Dunkelphosphorylierung nach Vorbelichtung hängt von der CO₂-Konzentration, von der Lichtintensität und der Zeit der Vorbelichtung ab. Unter den vorliegenden Bedingungen waren 7 min Vorbelichtung zur maximalen Förderung nötig. Die Halbwertzeit des Abklingens betrug etwa 4 min.Aus den Experimenten geht hervor, daß durch die Belichtung der Algen auch in vivo ein Zustand gebildet wird, der noch nach Belichtung eine Zeitlang im Dumkeln eine Erhöhung der ³²P-Einlagerung erlaubt.Es wird diskutiert, ob es sich einerseits um die Bildung einer im Licht reduzierten Substanz R handeln könnte, die für eine begrenzte Zeit in Dunkelheit noch einen cyclischen, mit Phosphorylierung gekoppelten Elektronentransport aufrechterhalten kann. Andererseits könnte durch die Vorbelichtung ein energiereiches Zwischenprodukt X _E — oder auch ein Protonenpool — gebildet werden, das bei dem Energietransfer vom Elektronentransportsystem zur ATP aufgebaut wird. Schließlich muß berücksichtigt werden, daß durch die Vorbelichtung an den Chloroplastenmembranen ein verstärkter ATP-Pi-Austausch zustande kommen könnte, der nach Belichtung nur langsam abklingt.

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Influence of preillumination on subsequent phosphorylation in the darkness of unicellular green algae (Ankistrodesmus braunii)

Summary Preilluminated unicellular green algae (Ankistrodesmus braunii) were treated in the subsequent darkness with ³²PO₄. The post-illumination dark incorporation was considerably increased compared with the control in continuous dark. The labeling of the separated phosphate-fractions was similar to that of continuous light. The light-induced dark incorporation depended from the light intensity as well as from the time of preillumination. A preillumination of 7 min was required for a maximal enhancement of this preillumination effect. On the other hand the effect diminished in darkness with a half life of approximately 4 min. Finally the enhancement was found to be greater in the absence of CO₂ than in the presence of CO₂.The experiments demonstrate the light-induced formation of a state in the algae, which permits the enhancement of ³²P-incorporation into several phosphate-fractions for a limited time during subsequent darkness.It is discussed, that this may be performed through the formation of a light-reduced substance R maintaining for a limited time a cyclic electron transport in darkness, coupled with phosphorylation. On the other hand it seems possible, that preillumination induces a high energy intermediate X _E—this could also be a pool of protons—formed in the course of energy-transfer from electron transport to ATP-formation. But we must consider also the possibility that light accellerates the ATP-Pi exchange on chloroplast-membranes for a time after preillumination.

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Abkürzungen ATP Adenosintriphosphat - ADP Adenosindiphosphat - Pi Orthophosphat - Poly-P anorganisches Polyphosphat - RNS Ribonucleinsäure - TCE Trichloressigsäure - 2,4-DNP 2,4-Dinitrophenol Stipendiat der Nishina-Gedächtnis-Stiftung (Japan) für 1963.     

Control of Mn status and infection rate by genotype of both host and pathogen in the wheat take-all interaction

Take-all is a world-wide root-rotting disease of cereals. The causal organism of take-all of wheat is the soil-borne fungus Gaeumannomyces graminis var tritici (Ggt). No resistance to take-all, worthy of inclusion in a plant breeding programme, has been discovered in wheat but the severity of take-all is increased in host plants whose tissues are deficient for manganese (Mn). Take-all of wheat will be decreased by all techniques which lift Mn concentrations in shoots and roots of Mn-deficient hosts to adequate levels. Wheat seedlings were grown in a Mn-deficient calcareous sand in small pots and inoculated with four field isolates of Ggt. Infection by three virulent isolates was increased under conditions which were Mn deficient for the wheat host but infection by a weakly virulent isolate, already low, was further decreased. Only the three virulent isolates caused visible oxidation of Mn in vitro. The sensitivity of Ggt isolates to manganous ions in vitro did not explain the extent of infection they caused on wheat hosts. In a similar experiment four Australian wheat genotypes were grown in the same Mn-deficient calcareous sand and inoculated with one virulent isolate of Ggt. Two genotypes were inefficient at taking up manganese and were very susceptible to take-all, one was very efficient at taking up manganese and was resistant to take-all, and the fourth genotype was intermediate for both characters. All genotypes were equally resistant under Mn-adequate conditions.     

Microwave fixation of the lung

A technique for microwave fixation of inflated rat lung is described. Conventional intratracheal fixation with instillation of fixative into the airways at a constant pressure results in pressure artifacts as well as flushing and disruption of cells and exudates. Microwave fixation fixes these elements in situ without disruption and thus is valuable when evaluating the distribution of inflammatory infiltrates. Exudative pneumonitis was produced in the rat using intratracheal instillations of either endotoxin or silica and comparisons were made between histologic sections fixed using either standard formalin fixation or microwave fixation.     

Blood–Brain Barrier Permeability to Sodium. Modification by Glucose or Insulin?

In order to explore the pathogenetic mechanism underlying the changes in blood-brain barrier sodium transport in experimental diabetes, the effects of hyperglycemia and of hypoinsulinemia were studied in nondiabetic rats. In untreated diabetes, the neocortical blood-brain barrier permeability for sodium decreased by 20% (5.6 +/- 0.7 versus 7.0 +/- 0.8 X 10(5) ml/g/s) as compared to controls. Intravenous infusion of 50% glucose for 2 h was associated with a decrease in the blood-brain barrier permeability to sodium (5.4 +/- 1.2 X 10(5) ml/g/s), whereas rats treated with an inhibitor of insulin-secretion (SMS 201-995, a somatostatin-analogue) had normal sodium permeability (7.3 +/- 2.0 X 10(5) ml/g/s). Acute insulin treatment of diabetic rats normalized the sodium permeability within a few hours as compared to a separate control group (7.7 +/- 1.1 versus 6.9 +/- 1.4 X 10(5) ml/g/s). To elucidate whether the abnormal blood-brain barrier passage is caused by a metabolic effect of glucose or by the concomitant hyperosmolality, rats were made hyperosmolar by intravenous injection of 50% mannitol. Although not statistically significant, blood-brain barrier sodium permeability increased in hyperosmolar rats as compared to the control rats (8.3 +/- 1.0 and 7.0 +/- 1.9 X 10(5) ml/g/s, respectively). It is concluded that either hyperglycemia per se or a glucose metabolite is responsible for the blood-brain barrier abnormality which occurs in diabetes. Further, we suggest that the specific decrease of sodium permeability could be the result of glucose-mediated inhibition of the Na+K+-ATPase localized at the blood-brain barrier.     

Quenching of Hoechst 33258 fluorescence in erythroid precursors.

Quenching of the fluorescence of DNA-bound Hoechst 33258 in erythroid precursors was studied by flow cytometry and cytochemistry. This quenching artifact may affect the measurement of ploidy in specific cases. The bone marrow cells of two patients with hemolytic disease and active erythropoiesis contained subpopulations of cells with an apparent hypodiploid DNA content as measured by flow cytometry of paraformaldehyde-fixed cells stained with Hoechst 33258. No aneuploidy was detected in either of the two cases when cells were stained with mithramycin or 7-aminoactinomycin D. Cells exhibiting reduced Hoechst 33258 fluorescence expressed glycophorin A and low amounts of CD36, and were therefore erythroid precursors. In one case studied, the number of cells with reduced Hoechst 33258 fluorescence and glycophorin A expressed agreed well with the number of cells containing nuclear hemoglobin. In the other case, hemoglobin was present in a significant proportion of nucleated cells. Calculated values for the efficiency of resonance energy transfer from Hoechst 33258 to hemoglobin were in accordance with the observed levels of quenching (approximately 10%). However, the results could also be explained by hemoglobin reabsorption of Hoechst 33258 fluorescence. Nuclei stained with Hoechst 33258 showed uniform fluorescence, probably due to extraction of hemoglobin during the isolation procedure.