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

Paired arbuscules in the Arum-type arbuscular mycorrhizal symbiosis with Linum usitatissimum

Experiments were conducted to investigate the "paired" arbuscules characteristic of Arum-type mycorrhizal colonization in Linum usitatissimum L. The development and senescence of arbuscular structures were followed in a time course study. Roots were freeze-sectioned longitudinally and mycorrhizal structures visualized using nitroblue tetrazolium, a vital stain to indicate metabolically active arbuscules and intercellular hyphae, followed by acid fuchsin counterstaining. Arbuscules were imaged using laser scanning confocal microscopy. The volume and surface area of each arbuscule of a developing paired structure were measured using three-dimensional imaging software. Arbuscules occurred in pairs in adjacent cortical cells arising from a single, radial intercellular hypha. These "paired" arbuscules often appeared to be at different developmental stages. Logistic regression and measurement of surface area indicated that there was a delay in initiation of the second arbuscule.Key words: Arum-type arbuscular mycorrhiza, double staining, metabolic activity, morphology, confocal microscopy, Linum usitatissimum. </jats:p