Relative amounts of soluble and insoluble forms of phosphorus and other elements in intraradical hyphae and arbuscules of arbuscular mycorrhizas
Megan H. Ryan A D , Margaret E. McCully B and Cheng X. Huang CA School of Plant Biology M081, University of Western Australia, 35 Stirling Hwy, Crawley, WA 6009, Australia.
B CSIRO Plant Industry, GPO Box 1600, Canberra, ACT 2601, Australia.
C Electron Microscopy Unit, Research School of Biological Sciences, Australian National University, Canberra, ACT 0200, Australia.
D Corresponding author. Email: megan.ryan@uwa.edu.au
Functional Plant Biology 34(5) 457-464 https://doi.org/10.1071/FP06242
Submitted: 13 November 2006 Accepted: 4 April 2007 Published: 17 May 2007
Abstract
Transport of phosphorus (P) into host plants and its release to root cells is an important function of arbuscular mycorrhizal fungi (AMF). However, relatively little is known about the forms and water solubilities of P compounds in specific locations in the intraradical fungal structures. We determined concentrations and solubility of P components in these structures in white clover (Trifolium repens L.). Plants were grown in the field (colonised by indigenous AMF) or in the glasshouse (inoculated with Glomus intraradices). Mycorrhizas were cryo-fixed in liquid nitrogen immediately (control) or after treatments designed to destroy cell membranes and extract solubles. Thirty to 70% of total P in hyphae and 100% in arbuscules was not extracted. The unextracted proportion of P was higher in the inoculated plants suggesting an environmental effect. It is proposed that the large component of non-extractable P in the arbuscules is involved in the tight regulation of inorganic P release to the host cells. In control roots magnesium, potassium and P were present in hyphae in molar ratios 1 : 2 : 4, further evidence that this relationship may be universal for AMF, and that other P-balancing cations are present but undetectable by the analytical technique.
Additional keywords: Glomus intraradices, phosphorus transfer at fungal/host interface, mycorrhizal roots, quantitative analytical cryo-SEM, Trifolium repens, polyphosphate, white clover.
Acknowledgements
We thank Tammy Edmonds-Tibbett for preparing the Glomus intraradices samples. The project was partly financed by the Grains Research and Development Corporation (GRDC). Megan Ryan was also funded by Meat and Livestock Australia (MLA).
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