Přednáška z Anatomie a fyziologie rostlin
| datum |
4.11.2014 |
| přednáší |
Dr. André-Marc Sellose (Muséum national d'Histoire naturelle, Paris, France, editor of New Phytologist) |
| název |
Mixotrophy: how mycorrhizal networks can make plant heterotrophic |
| anotace |
Most plants form mycorrhizal symbioses with soil fungi, which turn out to form networks between plants. The most dramatic evidence for such networks is the repeated emergence of mycoheterotrophy in plant evolution. Mycoheterotrophic plants are achlorophyllous and receive carbon (C) from surrounding green plants by way of shared mycorrhizal fungi. They recently made strong achievements due to two tools: molecular barcoding for fungal identification, and natural isotopic abundances (13C, 15N). Temperate mycoheterotrophs belong to orchids and Ericaceae, and associate with fungi that also form mycorrhizae with surrounding trees. Intermediate evolutionary steps were recently discovered in these families, in green forest species that use C from mycorrhizal fungi in addition to their photosynthesis. The so-called mixotrophic plants also use trees photosynthates by way of mycorrhizal networks, and phylogenies support that mixotrophy predisposed to evolution of mycoheterotrophy.
In green mixotrophic orchids, the survival of rare achlorophyllous variants (albinos) further supports mycoheterotrophic abilities, although they display a low fitness. Based on 13C abundances as a proxy of the fungal versus photosynthetic origin of C, we investigated C sources and allocations in mixotrophic perennial orchids. A unique pattern was discovered, where fungal C mostly supports belowground organs and young shoots, while later in the growth season, photosynthetic C mostly supports aboveground shoots and fruits, but not belowground reserves. Thus, loss of photosynthesis does not harm survival, but reduces fitness by seeds, and cannot be a direct evolutionary transition toward mycoheterotrophy, which likely requires more adaptations. These evidences support the evolutionarily metastability of mixotrophic nutrition.
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