FUNGI AND ITS RELATIONSHIPSWITH OTHER ORGANISMS Mutualistics Relationship Fungi and Plants: Mycorhizza, Lichen Parasitic Relationship Fungi and Animal or Insects Fungi and Humans
MUTUALISM vs PARASITISM Symbiosis: any situation where two different species live together. Mutualism – both partners benefit. Parasitism – only one partner benefits; typically reduces the fitness of other. Commensalism – two species live together without either harming the other, but where only one partners benefit. Mutualism and paratism were extensively studied.
MUTUALISTICS RELATIONSHIP WITHPLANTSMYCORRHIZA “Myco” meaning fungus, “Rhiza” meaning root. Mycorrhiza is a mutualistic relationship between a fungus in the soil and a plant root. Characteristics: 1) Can increase uptake of plant nutrients such as phosphorus and nitrogen especially when there is a low concentration / insoluble form of it in the soil. 2) Can assist nutrient uptake by plants from dilute solutions.
TYPES OF MYCORRHIZA1) Ectotropic2) Vesicular-arbuscular (V-A)3) Orchidaceous4) Ericaceous
Ectotrophic (sheating) Mycorrhiza Typically associated with temperate trees. Ex: Amanita muscaria (fly agaric) with birch or pine. Association: Mutualistic: fungus supplies plant with NH3 and PO43- from soil, plant supplies fungus with carbohydrates produced during photosynthesis.
Ectotrophic (sheating) MycorrhizaCharacteristics:1) Fungus forms highly developed sheath around roots. Mycelial strands extend into soil.2) Intercellular invasion of cortex to form Hartig’s net.3) Root hair formation suppressed (mycelium functional equivalent of root hairs). Root morphology altered.
Vesicular-arbuscular (V-A)Mycorrhiza Most widespread type of mycorrhiza. Associated with borophytes, ferns, spermatophytes (especially tropical trees). Ex: Endogone spp. with grasses. Association: Mutualistic: fungus supplies plant with NH3 and PO43- from soil, plant supplies fungus with carbohydrates produced during photosynthesis (same as ectotrophic mycorrhiza).
Vesicular-arbuscular (V-A)Mycorrhiza Characteristics: 1) No sheath. Fine hyphae extend to soil. 2) Intracellular penetration of middle cortex. No Hartig’s net. Fungus form characteristics vesicles and arbuscules. 3) Root hairs present. No apparent alteration of root morphology.
Orchidaceous Mycorrhiza Unique to orchid. Ex: Armillaria mellea (honey fungus) with Gastropodia elata. Association: Orchid parasitic on fungus. Peletons degenerate and supply orchid with sugars, vitamins and other nutrients obtained by saprophytic action of fungus outside root.
Orchidaceous Mycorrhiza Characteristics: 1) Same as V-A. 2) Intracellular penetration of inner cortex. Fungus forms characteristics coils (peletons). 3) ± root hairs.
Ericaceous Mycorrhiza Associated with heather and related plants. Includes Boletus and monotropa (bird’s nest plant) Association: Variable: achlorophyllous plant may be parasitic on fungus (monotropa type). Alternatively, mutualistic in heather type.
Ericaceous Mycorrhiza Characteristics: 1) Variable form; loose weft of hyphae surrounds root (heather) or definite sheath (Monotropa). 2) Intracellular penetration of outer cortex. In Monotropa a Hartig’s net may be additionally present. 3) No root hairs, no epidermal cells.
LICHENSMutualistic combination of an alga or blue-greenbacteria (cyanobacterium) with fungus.ORGANISM Mycobiont (fungus) There are ascomycetes or Basidiomycetes (rarely). They are ecologically obligate symbionts. Phycobiont (alga or bacterium) These are green algae (ex: Trebouxia, 70 % of all lichens) or blue-green (ex: Nostoc). They may be free living.
Main Features of LichensRELATIONSHIP BETWEEN ASSOCIATES Alga (phycobiont) produces and secretes carbohydrates Fungus (Mycobiont) may supply minerals to the alga. Uncertain, no experimental confirmation, phycobiont may be able to absorb its own minerals from the substrate. This association probably enables both partners to exploit habitat which would be unsuitable for either alone.STRUCTURE There is often a highly organised thallus, with algae forming a definite layer.
Three Types of Lichens MORPHOLOGY Crustose: crust like, Ex: Xanthoria which is the common yellowish lichen on gravestone. Foliose: Leaf like, Ex: Parmelia which is common in woodland. Fruticose: Shrubby, Ex: Cladonia which is common on acid heathland.
Lichens survive on bare rock, tree trunks,inhospitable places. Lichens growing on a rock. Lichens growing on trees.
Ecology and Applications ofLichens Lichen killed as SO2 levels rise. Used as indicator of atmospheric pollution. Lichens are so efficient at absorbing nutrients from the air that they can be used to monitor air quality because some kinds do not survive in polluted air. Breaking down rocks and starting the process of soil formation. Lichens or their products may be used as: Dyes (Harris tweed) Food (for reindeer herds) Antimicrobial (Usnea) Indicators (Litmus)