Lecture #9
Ectomycorrhiza
Ectomycorrhiza:
- hyphae do not penetrate cells of cortex in root tips
- hartig net: growth of hyphae in between and around cortex cells
- fungal mantle
- only form in actively growing roots
- 2000 spp. of plants
- 5000 spp. fungi
- most ectomyco. fungi unable to degrade cellulose
- obligate vs. facultative; enhanced by high light, decreased by high N & P levels
- e.g. Amanita, Russula, Lactarius, Laccaria, Cortinarius,
Inocybe, Boletus, Suillus
- know the difference between endo- and ectomycorrhiza and be able to give examples
How do mycorrhizal relationships form?
- feeder roots colonized by hyphae or germinating spore
- root exudate promotes spore germination and growth
- penetrate between cortex cells; form hartig net
- form fungal mantel
- extension of hyphae from mantel into soil
Unique root growth and morphology
- fungus secretes auxins, giberellins, & cytokinens; all plant growth hormones
- enhances root growth
- maintains juvenile roots; no root hairs
- mycorrhizal root tip is more often branched than nonmycorrhizal root tip, e.g., dicotomous branching in Pinaceae
What does fungus get from plant?
- sugars (monosaccharides) that are transported from the plant to the fungus and converted into trehalose, mannitol & glycogen, which are generally not permeable back across fungal cell membrane
- B vitamins; stimulate spore germination
- estimated that trees invest 10% of photosynthates to their mycobionts
What does plant get from fungus?
- phosphorus, calcium, potassium, copper, molybdenum, magnesium, zinc
- nitrogen
- water: source-sink and water potential
- protection against pathogens
Ectomycorrhiza dynamic process
- succession:
- individual mycorrhiza active for 1-3 yrs
- root may out grow fungus and be colonized by a alternative ectomycorrhizal fungus or a more aggressive ectomycorrhizal fungus may replace the previous
- a single tree will often have several mycorrhizal partners throughout its root system; its not one tree one fungus
- the most conspicuous and prolific mycorrhizal fruiting population above ground may not be the dominant mycorrhizal partner
- not all mycorrhizae are beneficial to all stages of host life period
Ectendomycorrhiza
- characteristics of ectos but exhibit intracellular penetration
- MRAs Mycelium radicis atrovirens; dark septate mycorrhiza;
ascomycetes
Orchid mycorrhiza
- orchid seeds and young plants associated with Rhizoctonia
- seeds and seedlings apparently lack some enzymatic machinery; can't metabolize sulfer
- many orchids are achlorophyllous; get carbon from fungus
- Rhizoctoniais normally a potent pathogen of plant; often considered to be captured by the orchid; orchids produce many secondary products that may inhibit fungus
- don't have any major effect on root morphology
- form loops in root cells
- other orchid mycorrhizae (JS Edits LATER)
Ericoid mycorrhiza
- mycorrhiza of the Ericales (Ericaceae, Monotropaceae); some do have true ectomycorrhiza
- 2 forms; one with mantel, Hartig net; one with no mantel, Hartig net but invades cortex cells
- on fine root system
- extensive hyphal development around root; slight development on root surface; within cells extensive hyphal coils
- fungus eventually degenerates but so does cortex cell
- Mycelium radicis myrtillis
Arbutoid mycorrhiza
- described in Arbutus
- similar to ectomycorrhiza in root morphology
- mantle, Hartig net
- epidermal cells are colonized by hyphae that form coils; coils disintegrate but cells do not; may be colonized again
- Cortinarius, Cenococcum
- Review general ectomycorrhiza notes from lecture #5