Oxidation and reduction of cytochrome oxidase in the neonatal brain observed by in vivo near-infrared spectroscopy.

Near-infrared spectroscopy was used to determine the relationship between the redox state of mitochondrial cytochrome oxidase CuA and haemoglobin oxygenation in the isoflurane-anaesthetized neonatal pig brain. Adding 7% CO2 to the inspired gases increased the total haemoglobin concentration by 8 microM and oxidized CuA by 0.2 microM. Decreasing the inspired oxygen fraction to zero for 90 s dropped the oxyhaemoglobin concentration by 27 microM and reduced CuA by 1.8 microM. However, no change in the CuA redox state was observed until oxyhaemoglobin had decreased by more than 10 microM. The response of the CuA redox state to these stimuli was very similar following 80% replacement of the haemoglobin by a perfluorocarbon blood substitute; this demonstrates that the results in the normal haematocrit were not a spectral artefact due to the high haemoglobin/cytochrome oxidase ratio. We conclude that the large reductions in the CuA redox state during anoxia are caused by a decrease in the rate of oxygen delivery to the cytochrome oxidase oxygen binding site; the small oxidations, however, are likely to reflect the effects of metabolic changes on the redox state of CuA, rather than increases in the rate of oxygen delivery.

Ostracod reactions to non-toxic and toxic algae.

When fed algae continuously, laboratory ostracods had a life span of 21-28 days; without food, they were able to survive about 7 days. When exposed to thick suspensions of gas-vacuolate blue-green algae, survival rates were generally low. Twenty five % of our euplanktonic strains killed entire ostracod populations within 24-48 hrs; about 30% of other waterbloom strains were dangerous to ostracods causing either death or coordination loss. Some amphibious non-gas-vacuolated strains were also toxic to ostracods. Toxins from broken cells were not persistent in effect; ostracods surviving the initial shock often appeared recovered within 2-4 days. In di-algal systems, ostracods generally fed on a single species and did not always choose green algae over blue-green. Unicellular green algal strains (Ankistrodesmus, Scenedesmus, Kirchneriella) were generally preferred. Some chlorophycean forms (Zygnema, Hormidium, Trentepholia) were shunned in favor of bluegreens such as Tolypothrix and Westiella. Erect and branched strains (Fischerella, Westiella, Tolypothrix) were eaten before Anabaena and Nostoc with the latter genus being least preferred. Intact Nostoc colonies were usually not ingested, but some loosely growing, non-toxic strains of both Nostoc and Anabaena provided adequate food for ostracod populations indefinitely.

Nitrogen fixation by gloeocapsa.

The continuous growth in a medium free of combined nitrogen and the experimental production of ethylene via acetylene reduction indicate that nitrogen fixation by blue-green algae is not solely confined to filamentous genera with heterocysts. Axenic cultures of Gloeocapsa sp., adapted to nitrate-free medium, form ethylene at rates comparable to those of species known to fix nitrogen.