School of Sciences, Lautoka Campus BIO509 Botany Lecture 10: Symbiotic relationships between fungi and other organisms.

Learning objectives Know the kinds of symbiotic relationships that exist between fungi and other organisms. Understand and appreciate their importance.

There are a wide array of symbioses. Symbiosis Comes from a Greek word meaning “living together” It is a permanent or long-lasting association between two or more different species. Occur when two or more different species depend on each other for food, shelter, or protection. There are a wide array of symbioses.

mutualism - injured or harmed parasitism In symbiosis, at least one member of the pair benefits from the relationship. The other member may be - injured or harmed  parasitism - relatively unaffected -   commensalism - may also benefit   mutualism

Mycorrhizae Are modified roots consisting of symbiotic associations of fungi and roots. Almost all plant species have mycorrhizae. Fossilized roots from some early plants include mycorrhizae - one of the evolutionary adaptations that made it possible for plants to colonize the lands.

Mutualistic relationship between fungus and roots Both fungus and roots benefit. Fungus absorbs and concentrates phosphorous. Fungus forms a mantle of million thread like stands that facilitate absorption of water and nutrients.

Essential to normal growth and development of many plants. Fungus provides protection from pathogenic fungi and nematodes. Host plant provides carbohydrates and vitamins for fungal growth.

Two types of mycorrhizae

Ectomycorrhizae Mycelium forms a dense sheath or mantle over the root surface. Hyphae extend over the root surface increasing the surface area for water and mineral absorption. Root cells are not penetrated by the hyphae Common in woody plants such as pine, spruce, oak, walnut, birch, willow and eucalyptus families.

Endomycorrhizae Do not form a mantle. May and may not penetrate the root cells Forms dense knotlike structures called arbuscules. Much more common than ectomycorrhizae Occurs in over 90% plant species including important crop plants.

Human and ecological significance of mycorrhizae Help in plant establishment on nutrient poor soils. Increase plant growth in short time period (forestry). Reduce fertilizer requirements. Cut down production costs. Decrease fertilizer contamination of the environment

Lichens

A lichen is a mutualistic relationship between a fungus (mycobiont) and an alga and/or a cyanobacterium (photobiont). In the case of lichens the symbiosis results in an organism that looks completely different to either the fungal or photosynthetic partner. The combination of photosynthetic and fungal cell creates something new.

The fungal component is most commonly an ascomycete The fungal component is most commonly an ascomycete. Basidiomycete lichen are also known to occur. Fungus gives the lichen its overall shape and structure. Fungus provides alga with suitable physical environment for growth. Alga provides fungus with food. There major growth forms of lichens – crustose, fruticose, foliose.

Fruticose (shrubby) lichens

Crustose lichens

Foliose (leafy) lichens

Lichens absorb most of the minerals needed from the air or from the rain water. Physical arrangement of hyphae retains water and minerals, allows gas exchange and protect the algae. Fungal pigments shade the algae from intense sunlight.

Soredia Ascocarp of fungus Fungal hyphae Algal layer Algal cell

Reproduction of lichen Fungus of lichen reproduces sexually by producing ascocarp or basidiocarp. Algae reproduce by asexual cell division. Lichen as dual organism reproduce through asexual reproduction by production of symbiotic units called soredia.

Human and Ecological relevance if Lichens Lichens are extremely sensitive to sulphur dioxide. The amount of sulphur in the air can be determined by the appearance and disappearance of lichens. Lichens do not exist in industrial environment with SO2 emissions. Lichens are also very sensitive to nuclear radiation.

Acids produced by lichens destroy historical ruins and exposed rocks. Lichens provide food for some animals. (reindeer, North African sheep) Many have been investigated for antibiotic properties. Extracts are used in soap and perfumes.

Questions??