Symbioses: Plant, Animal, and Microbe Interactions
Cameron, Duncan D , Leake, Jonathan R , Read, David J .
Are orchids parasitic on their mycorrhizas or do they live by carbon credit and repayment?
The overwhelming majority of plants are reliant upon symbiotic associations with fungi (mycorrhizas). Traditionally, the mycorrhizal symbiosis is considered to be characterised by the supply of carbon (C) from plant-to-fungus in exchange for nutrients transferred from fungus-to-plant. Orchids were amongst the first plants in which mycorrhizal associations were recognized to be beneficial, but the extent to which this symbiosis benefits the fungal partners is uncertain. A defining feature of orchid mycorrhiza is that during symbiotic germination and establishment of the tiny dust seeds of orchids there is net flux of both C and nutrients from fungus-to-plant so the relationship appears not to be mutualistic. Most adult orchids develop green leaves and thus have potential to supply photosynthate in exchange for fungal-acquired mineral nutrients in a fully mutualistic relationship as seen in arbuscular-, ecto- and ericoid mycorrhiza. However, such mutualism has never been established for any orchid. In the present study, using isotopically labelled (14C, 13C and 15N) amino acids supplied to external mycelium of the fungus and 14CO2 supplied to the plant shoots, we demonstrate that a net flow of photosynthate-derived C from plant-to-fungus can occur in the mycorrhizal association between the green forest orchid Goodyera repens and its fungal symbiont Ceratobasidium cornigerum. In return for this C, the fungus supplies nutrients taken up through the mycelial network back to the adult orchid. This study demonstrates for the first time (1) mutualism in orchid mycorrhiza, (2) bi-directional transfer of C between a green orchid and its fungal symbiont, and (3) a fungus-dependent pathway for organic N acquisition by an orchid. These findings suggest that the investment of fungal C in seedling establishment may be repaid with interest by adult orchid photosynthate.
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Web page for Dr. Duncan Cameron
1 - University of Sheffield, Department of Animal and Plant Sciences, Alfred Denny Building, Western Bank, Sheffield, South Yorkshire, S10 2TN, UK
Presentation Type: Oral Paper:Papers for Topics
Location: Blair A/Gage
Date: Tuesday, July 29th, 2008
Time: 10:00 AM