Argon,xenon, hydrogen,and the oxygen consumption and glycolysis of mouse tissue slices

The effects of xenon, argon, and hydrogen on the aerobic and anaerobic metabolism of mouse liver, brain, and sarcoma slices have been investigated. Xenon was found to alter the rates of metabolism of these tissues in a manner almost identical with helium. The gas increased the rate of oxygen consumption in all three tissues and significantly depressed that of anaerobic glycolysis in brain and liver. The depression of glycolysis in sarcoma was less pronounced and not highly significant. Although both the magnitude and statistical significance of the effects observed with argon were much smaller, there was a seeming adherence to the general pattern established by xenon and helium. Hydrogen while remaining essentially ineffective insofar as oxygen uptake was concerned, depressed glycolysis in both liver and brain slices but did not significantly affect sarcoma slices. The following points are stressed in the Discussion: (1) the magnitude and direction of effects exerted by helium, argon, xenon, hydrogen, and nitrogen do not conform with the relative values of molecular weight, density, and solubility of these gases; (2) the effect of these gases on tissue metabolism does not necessarily parallel that exerted upon the whole organism.     

Cyclic Changes in Chloroplast Structure in Synchronized Euglena gracilis*

SYNOPSIS. In populations of Euglena gracilis strain Z synchronized by cultivation on a repetitive light-dark cycle, chloroplasts undergo cyclic changes in structure. During most of the light period chloroplasts are relatively compact with closely appressed lamellae; during the dark (division) period the chloroplasts become quite distended. This change persists for at least one cycle even when the cells are left in continuous light, suggesting that the periodicity may be related more to the age of the cell than to a direct effect of light. In addition, the pyrenoid in synchronized cells has a transient existence, being present only in the first half of the light period.     

The gall-inducing habit has evolved multiple times among the eriococcid scale insects (Sternorrhyncha: Coccoidea: Eriococcidae)

The habit of inducing plant galls has evolved multiple times among insects but most species diversity occurs in only a few groups, such as gall midges and gall wasps. This phylogenetic clustering may reflect adaptive radiations in insect groups in which the trait has evolved. Alternatively, multiple independent origins of galling may suggest a selective advantage to the habit. We use DNA sequence data to examine the origins of galling among the most speciose group of gall-inducing scale insects, the eriococcids. We determine that the galling habit has evolved multiple times, including four times in Australian taxa, suggesting that there has been a selective advantage to galling in Australia. Additionally, although most gall-inducing eriococcid species occur on Myrtaceae, we found that lineages feeding on Myrtaceae are no more likely to have evolved the galling habit than those feeding on other plant groups. However, most gall-inducing species-richness is clustered in only two clades ( Apiomorpha and Lachnodius  +  Opisthoscelis ), all of which occur exclusively on Eucalyptus s.s . The Eriococcidae and the large genus Eriococcus were determined to be non-monophyletic and each will require revision.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 83 , 441–452.     

Bicarbonate Transport and Alkalization of the Medium by Four Species of Rhodophyta

Photosynthesis by four species of Rhodophyta: Ceramium rubrum,Ceramium tenuissimum, Gelidium crinale and Pterocladia capillaceawas optimal at 25 to 30?C and at pH 8.0 to 8.5. The measuredrates of photosynthesis exceeded the rate which could be supportedby the carbon dioxide arising from the dehydration of bicarbonatein the medium, from 2.7- to 10.9-fold at pH 8.0 and from 9-to 33.4-fold at pH 9.0, in the absence of measurable extracellularcarbonic anhydrase activity. Assays for malic enzyme and pyruvate,orthophosphate dikinase were negative, indicating that bicarbonateions are taken up by a transport system rather than by an accessorycarbon fixation pathway. When the algae were allowed to photosynthesizein an unbuffered system a DCMU (3-[3', 4'-dichlorophenyl]-1,1-dimethylurea)-sensitive alkalization of the medium was observed.This alkalization was shown to have a 1:1 stoichiometry withphotosynthetic carbon fixation. Alkalization of the medium occurredfrom 3.4 to 5.8 times the theoretical rate of supply of hydroxylions arising from the dehydration of bicarbonate. The data areconsistent with the operation of a bicarbonate transport systemin these macroalgae, in which electrical neutrality and pH balanceare maintained by hydroxyl ion efflux. A difference observedbetween the time-course of alkalization and oxygen evolutionsuggests that the transport of the two ions is not compulsorilycoupled. Key words: Bicarbonate transport, alkalization of the medium, Rhodophyta