The respiration of insects at reduced pressures II. The uptake of oxygen by Tenebroides mauritanicus

The respiration of larvae of Tenebroides mauritanicus exposed to reduced pressures in air was measured in a specially designed chamber by means of gas chromatography. Both O₂ uptake and CO₂ output were progressively reduced as the pressure was lowered from 200 to 35 mm Hg. There were differences in the amounts of gases exchanged when the insects were exposed under dry or moist conditions. When expired CO₂ was allowed to accumulate, in some experiments it had a marked stimulating effect on O₂ uptake between 60 and 200 mm. The respiratory quotient at the various pressures was calculated and the values found under different conditions of pressure and moisture are discussed.

---

Zusammenfassung In der ersten Veröffentlichung dieser Reihe beschrieben Monro, Dumas und Buckland (1962) die Kohlendioxyd-Ausatmung der Larven von T. mauritanicus bei verringertem atmosphärischen Druck. Unter 65 mm nahm die CO₂-Ausatmung deutlich und fortschreitend ab. Um zu zeigen, daß dieser Verringerung der CO₂-Produktion tatsächlich eine Abnahme der Atmung entspricht, wurde ein Apparat entwickelt, mit dessen Hilfe O₂-Aufnahme und CO₂-Abgabe der Insekten gaschromatographisch gemessen werden konnten.Bei dreistündiger Exposition wurde unter den experimentellen Bedingungen gefunden, daß sich im Vergleich mit der Reaktion bei höherem Druck sowohl O₂-Aufnahme als auch CO₂-Abgabe bei 100, 60 und 30 mm fortschreitend verringert. Bei so niedrigem Druck war die Atmung während der Expositionszeit gleichmäßiger als bei höherem Druck, bei dem von Zeit zu Zeit deutliche Schwankungen auftraten. Bemerkenswert war ein deutlicher Unterschied in der Respirationsrate bei feuchtigkeitsgesättigter Luft und unter trockenen Bedingungen. Bei hoher Luftfeuchtigkeit war die O₂-Aufnahme zwischen 100 und 400 mm größer als bei Trockenheit und die CO₂-Abgabe war größer von 65 mm aufwärts. Daraus wird gefolgert, daß in diesem Druckbereich bei Trockenheit der Austausch beider Gase durch dauernden oder zeitweisen Verschluß der Atmungswege behindert wird.In einigen Versuchen wurde CO₂ durch Absorption aus der die Insekten umgebenden Atmosphäre entfernt. Abwesenheit von CO₂ verringerte die O₂-Aufnahme im Bereich von 60–200 mm besonders bei Feuchtigkeit. Bei Trockenheit war die O₂-Aufnahme bei hohem CO₂-Gehalt signifikant geringer. Hier mag wiederum Schließung der Atmungswege die stimulierende Wirkung des CO₂ vermindert haben.Berechnungen des Respirationsquotienten aus den verfügbaren Daten zeigen eine stetige Abnahme dieses Wertes mit abnehmendem Druck bei Feuchtigkeit, während der R.Q. in trockener Umgebung bei jedem Druck ziemlich konstant blieb. Es werden keine endgültigen Schlüsse aus diesen Berechnungen gezogen, aber es wird angenommen, daß die feuchte Umgebung einen freieren Gasaustausch durch die Atmungswege erlaubt und daher bessere Bedingungen zur Bestimmung des tatsächlichen R.Q.-Wertes bei vermindertem Druck bietet.

---

---

In this paper pressures are given as absolute pressures expressed in mm Hg.     

Further observations on the effect of ethionine on the synthesis of β-galactosidase inEscherichia coli: Formation of an immunologically cross-reacting protein

It was found that ethionine partially inhibits the transport of the inducer (TMG) of β-galactosidase into the cells ofEscherichia coli ML-30. The synthesis of β-galactosidase-specific messenger RNA is not inhibited. Ethionine appears to be incorporated into proteins synthesized by the strains used. The incorporation of ethionine into the molecule of β-galactosidase results in the synthesis of an enzymically inactive, immunologically cross-reacting protein.     

Presence and oxidation of amino acids in rhizosphere and non-rhizosphere soil

Manometric studies were carried out on the respiratory activity of different rhizosphere and non-rhizosphere soils to follow quantitatively the over-all microbial activity in the rhizosphere soil as affected by the species and growth phase of plant. Oxygen consumption was distinctly greater in rhizosphere soils as compared to that in non-rhizosphere soils. The difference between oxygen consumption by rhizosphere and non-rhizosphere soils changed with the course of plant growth and it was not the same in different plants. This difference in oxygen consumption might be a measure of the amount of available oxidizable substrate in the rhizosphere. A rhizosphere sample had greater diversity as well as higher concentration of free amino acids than a non-rhizosphere sample of the same soil. Bacterial counts pointed to preferential stimulation in the rhizosphere of bacteria requiring individual amino acids. amino acids, such as glycine, alanine, asparsic acid of tyrosine were oxidized more rapidly in rhizosphere than in non-rhizosphere soil, but the extsent of oxidation for each of the amino acids studied did not differ. The amount of oxygen consumed during oxidation of alanine, aspartic acid or tyrosine was about one-half of the total amount necessary for complete oxidation. With glycine a higher extent of oxidation (60%) was observed. These extents of oxidation of glycine and aspartic acid did not change on investigation at two different phases of plant growth.     

Mycoplasma-like bodies in plants infected with potato witches' broom disease and the response of plants to tetracycline treatment

The virus origin of a Czechoslovak isolate of potato witches' broom disease is discounted: electron micrographs of ultrathin section of phloem tissues from plants infected with potato witches' broom disease demonstratedMycoplasma-like bodies, spherical or elongated showing binary fission and fragmentation. The minute corpuscles have a diameter of about 50–60 nm, the largest bodies of 1000 nm. The width of elongated filamentous structures is about 200 nm, most oval bodies have a diameter of 250 nm. A weak tetracycline treatment of diseased plants causes a delay of symptom development; a strong dose of tetracycline (applied by means of the wick method into the stem) inhibits symptom appearance completely. Tetracycline produces a phytotoxic effect inhibiting the growth of tomato plants and causing (at higher concentrations) necrosis and death of these plants. There is a note in the paper dealing with the term “mycoplasma”. The word mycoplasma in the sense ofEriksson (1897) or ofMereschkowsky (1910) does not correspond to the genus nameMycoplasma Nowak (1929).     

The dependence of the frequency of recessive lethal and vital mutations inArabidopsis thaliana (L.)Heynh. on the concentration of N-nitroso-N-methylurea

The dependence of the frequency of recessive lethal (two groups), chlorophyll and morphological mutations on the mutagen concentration was determined in M₂ after subjection to N-nitroso-N-methylurea applied to seeds ofArabidopsis in three concentrations (0·05, 0·10 and 0·20mm). The observed frequencies were compared with the theoretically expected ones for the linear and for two exponential types of dependence, by using the t-test, according to the formulas m=k. C, m=k. C^3/2, m=k. C². No satisfactory agreement with any expected type of dependence was found when directly observed frequencies were used. Since a considerable deficit of mutation frequency was observed in high concentrations, the correction of frequency values was done with respect to the probability of occurence of double mutations. After such a correction, a clear exponential relation was found in both types of lethals and a linear one in chlorophyll and morphological mutations. The probable occurence of multiple mutations should be, therefore, taken into account if the dependence of mutation frequency on the concentration of mutagen is discussed.