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Biomedical subjects

J A Raven

Publications and source records attributed to J A Raven.

8 recordsLinked to original sources
PubMed1986

Plasticity in algae.

Unicellular planktonic algae show considerable developmental plasticity in relation to mean cell size and the fraction of the cell volume occupied by various organelles. Changes in cell size and composition in relation to variations in the supply of light and nutrient solutes have been partially characterized with respect to the signals which regulate the changes, and in terms of the possible significance of the changes in maximizing growth rate under different resource-limited conditions. Less is known of the mechanisms by which the signals lead to the observed phenotypic effects. Multicellular attached macroalgae, whether acellular or multicellular, rhizophytic or haptophytic, have greater scope for phenotypic modification of morphology than do microalgae, in addition to the possibility of biochemical (compositional) changes. In addition to biochemical changes in response to variations in the ratio of availability of various resources (photons, N, P) there are also structural changes; significant here is the increased occurrence of (often colourless) hairs in haptophytes and (probably) of enhanced rhizoid development in rhizophytes. Many of the changes in morphology and physiology of macroalgae in response to changes in photon and nutrient supply have analogies in the behaviour of vascular plants (especially of aquatic vascular plants).

Adaptation, Physiological↗
PubMed1967

Ion transport in Hydrodictyon africanum.

The concentrations of K, Na, and Cl in the cytoplasm and vacuole, the tracer fluxes of these ions into and out of the cenocyte, and the electrical potential difference between bathing solution and vacuole and cytoplasm, have been measured in Hydrodictyon africanum. If the ions were acted on solely by passive electrochemical forces, a net efflux of K and Cl and a net influx of Na would be expected. Tracer fluxes indicate a net influx of K and Cl and efflux of Na in the light; these net fluxes are consequently active, with an obligate link to metabolism. The effects of darkness and low temperature indicate that most of the tracer K and Cl influx and Na efflux are linked to metabolism, while the corresponding tracer fluxes in the direction of the free energy gradient are not. Ouabain specifically inhibits the metabolically linked portions of tracer K influx and Na efflux. Alterations in the external K concentration have similar effects on metabolically mediated K influx and Na efflux. It would appear that K influx and Na efflux are linked, at least in the light.

Biological Transport, Active↗
PubMed1967

Light stimulation of active transport in Hydrodictyon africanum.

The mechanism of light stimulation of active K and Cl influx and active Na efflux, in Hydrodictyon africanum has been investigated using different wavelengths of red light and different gas mixtures, and the inhibitors DCMU and CCCP. The active Cl influx requires photosystem 2, since its relative quantal efficiency falls with increasing wavelength of red light, and it is as sensitive to the inhibitor DCMU as is photosynthesis; it is relatively insensitive to the uncoupler CCCP. The active K influx and active Na efflux are inhibited by CCCP, but the relative quantal efficiency of these processes increases with increasing wavelength of red light, and they are relatively insensitive to DCMU. These cation fluxes can be supported by cyclic photophosphorylation, whereas Cl influx needs photosystem 2 but probably not ATP.

Biological Transport, Active↗