Der Effekt der Ektomykorrhiza auf die Aufnahme und Verteilung von Calcium in Sämlingen von Pinus sylvestris L.

Abstract

The objective of this thesis was to investigate the influence of ectomycorrhiza on the uptake and distribution of calcium in pine seedlings (Pinus sylvestris). A focal point of interest was the apoplastic permeability of the fungal sheath of the fungi Suillus bovinus and Rhizopogon roseolus. Using different methods (micro- and macroautoradiography, liquid scintillation spectrometry, atom absoption spectrometry, EDXS), the distribution of calcium within the mycorrhizae and the uptake into the shoots were examined in order to obtain detailed knowledge of the transport processes in the mycorrhizal roots.Using the radiotracer 45Ca, an apoplastic transport through the fungal sheath of the fungi Suillus bovinus and Rhizopogon roseolus could be proven. This was shown by microautoradiographs, which established radioactive marking in the cell walls of the fungal sheath, the harting net and the stele. However, a part of the calcium was precipitated by the fungi by means of exudation of oxalic acid in form of calciumoxalat, and therefore existed in a physiologically inactive form. Another part of the disposable calcium was bound to free cation-binding sites of the cell walls, and therefore temporarily unavailable for transport into the shoot. The absence of the fungal sheath and its ?buffer-effect? explains the faster transport of 45Ca into the shoot of non-mycorrhizal pine. The transport capability of calcium into the shoot was also a distinguishing factor between the two fungal partners. Rhizopogon roseolus displayed a higher calcium intake, which can be explained by its thinner fugal sheath. Additionally, using X-ray microanalysis, higher S-contents could be shown to exist in the cell walls of Suillus bovinus. This could be an indication for a higher hydrophobin accumulation and therefore also a higher hydrophobicity compared to Rhizopogon roseolus. Exposure in an aqueous milieu resulted for Suillus bovinus in lower S-contents, which can be explained by a diffusion of the hydrophobines into the surrounding medium.Experiments with different external calcium concentrations (1mM and 50 mM) showed that an increased calcium supply primarily influenced the calcium concentration in the shoots of the non-mycorrhizal pines. While the calcium was transported relatively freely into the shoot by the non-mycorrhizal roots, the ectomycorrhizae held back part of the excess calcium. Investigating the vacuolar polyphosphate granules of the fungal partners it could be shown that the composition of Suillus bovinus strongly depended on external factors. It could be proven that in the presence of a surplus of calcium, even when using cryotechiques, calcium is nevertheless present to a large degree in the polyphosphate granules.In this thesis it could be shown that the apoplastic transport of calcium through the fungal sheaths of Suillus bovinus and Rhizopogon roseolus is possible. However, a part of the calcium is held back by the mycorrhizae, and is therefore temporarily unavailable for further transport into the shoot. Most important for the transport processes in the fungal sheaths are, beside the species of the symbiotic partners, the form of the fungal sheaths and the experimental conditions.