Elemental composition in vesicles of an arbuscular mycorrhizal fungus, as revealed by PIXE analysis

We investigated element accumulation in vesicles of the arbuscular mycorrhizal (AM) fungus Glomus intraradices, extracted from the roots of inoculated leek plants. The elemental composition (elements heavier than Mg) was quantified using particle-induced X-ray emission (PIXE), in combination with scanning transmission ion microscopy (STIM). In vesicles, P was the most abundant of the elements analysed, followed by Ca, S, Si and K. We analysed 12 vesicles from two root systems and found that the variation between vesicles was particularly high for P and Si. The P content related positively to Si, Zn and K, while its relation to Cl fitted to a negative power function. Vesicle transects showed that P and K were present in central parts, while Ca was present mainly near the vesicle surfaces. The results showed that P is an important part (0.5% of the dry weight) of the vesicle content and that the distribution of some elements, within mycelia, may be strongly correlated.