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¹³C Incorporation into Signature Fatty Acids as an Assay for Carbon Allocation in Arbuscular Mycorrhiza

Olsson, Pål Axel, van Aarle, Ingrid M., Gavito, Mayra E., Bengtson, Per, Bengtsson, Göran
Applied and environmental microbiology 2005 v.71 no.5 pp. 2592-2599
Glomus intraradices, vesicular arbuscular mycorrhizae, lipogenesis, long chain fatty acids, lipids, carbon, stable isotopes, isotope labeling, Gigaspora margarita, mycelium, roots, nutrient transport, symbiosis, Allium porrum, leeks, Plantago lanceolata, Trifolium subterraneum
The ubiquitous arbuscular mycorrhizal fungi consume significant amounts of plant assimilated C, but this C flow has been difficult to quantify. The neutral lipid fatty acid 16:1[omega]5 is a quantitative signature for most arbuscular mycorrhizal fungi in roots and soil. We measured carbon transfer from four plant species to the arbuscular mycorrhizal fungus Glomus intraradices by estimating ¹³C enrichment of 16:1[omega]5 and compared it with ¹³C enrichment of total root and mycelial C. Carbon allocation to mycelia was detected within 1 day in monoxenic arbuscular mycorrhizal root cultures labeled with [¹³C]glucose. The ¹³C enrichment of neutral lipid fatty acid 16:1[omega]5 extracted from roots increased from 0.14% 1 day after labeling to 2.2% 7 days after labeling. The colonized roots usually were more enriched for ¹³C in the arbuscular mycorrhizal fungal neutral lipid fatty acid 16:1[omega]5 than for the root specific neutral lipid fatty acid 18:2[omega]6,9. We labeled plant assimilates by using ¹³CO₂ in whole-plant experiments. The extraradical mycelium often was more enriched for ¹³C than was the intraradical mycelium, suggesting rapid translocation of carbon to and more active growth by the extraradical mycelium. Since there was a good correlation between ¹³C enrichment in neutral lipid fatty acid 16:1[omega]5 and total ¹³C in extraradical mycelia in different systems (r² = 0.94), we propose that the total amount of labeled C in intraradical and extraradical mycelium can be calculated from the ¹³C enrichment of 16:1[omega]5. The method described enables evaluation of C flow from plants to arbuscular mycorrhizal fungi to be made without extraction, purification and identification of fungal mycelia.