The development of endomycorrhizal root systems VIII. Effects of soil phosphorus and fungal colonization on the concentration of soluble carbohydrates in roots

Concentrations of phosphorus in shoot and soluble carbohydrates (fructose, glucose, sucrose and fructans) in root were measured in non-mycorrhizal and vesicular-arbuscular (VA) mycorrhizal (Glomus mosseae) leek plants (Allium porrum) raised at six concentrations of soil phosphate. In conditions when an increased concentration of soil phosphate reduced VA mycorrhizal infection, the concentrations of soluble carbohydrates in the root were at a maximum. Therefore the hypothesis that greater concentrations of soluble carbohydrates in roots favour VA mycorrhizal infection is discounted. There was a specific effect of VA mycorrhizas, in that infected roots contained a larger concentration of sucrose than did uninfected roots, in plants with similar phosphorus concentrations in dry matter of shoots. We conclude, first, that increased phosphorus supply from either phosphate addition to soil or VA mycorrhizal infection increases concentration of soluble carbohydrates in leek roots and, secondly, that the VA mycorrhizal root behaves as a particularly strong physiological sink when there is an excess concentration of sucrose in the host

Hemispheric contribution to vertex augmentation/reduction of the auditory evoked potential

Starting off from the notion that the cerebral hemispheres differ in their processing mode, this paper reports on stimulus intensity modulation of auditory evoked potentials recorded from hemispheric leads (C3 and C4 referenced to ipsilateral mastoid processes) in a sample of 40 male Ss between 18 to 40 years of age. The experimental set up involved the recording of series of 100 trials to binaural clicks of 63.5, 74.6 and 85dB AL. Ss who were augmenters at the vertex showed positive Amplitude-Intensity function slopes over the left hemisphere; when Ss were Reducers at the vertex, the slopes were negative on the right hemisphere. These results are interpreted in terms of attention deployment or allocation to one or the other hemispheric processing mode. This might constitute a trait-like enduring subject characteristic whose relation to traditional psychometric variables needs further exploration. The modality especificity of this phenomenon is also discussed

Low-level electrical currents and brain indicators of behavioral activation

Distinguishing between slow brain potential correlates of arousal and activation on the basis of their functional role and temporal involvement during a reaction-time task, data are presented which suggest that weak electrical polarizing currents applied to the head in human subjects modify predominantly activation indicators rather than arousal ones