Quiz sur les lichens

Lichens

• Lichens are a symbiotic association, typically between a fungus (mycobiont) and an alga or cyanobacterium (photobiont).
• They are a significant portion of Ascomycota.
• Lichens are visually distinct organisms, unlike their component parts.
• There are cases where more than two organisms are involved.
• Lichen formation involves a unique morphogenetic process.
• Laboratory attempts to reproduce lichen growth have yielded limited results.

Traditional vs New Vision of Lichens

• The traditional view of lichens considers them a two-organism relationship (fungus and an alga or cyanobacterium).
• Current research shows the involvement of other organisms, including fungi and bacteria, within the lichen symbiosis.
• Recent studies using metatranscriptomics suggest lichens may have three (or more) partners, including a basidiomycete.

Lichen Morphology

• Lichens' thallus (body) typically has distinct layers containing the symbionts—the alga or cyanobacteria and the fungus.
• Soralia are structures for asexual reproduction, containing algal cells enclosed in fungal hyphae.
• Different types of vegetative reproduction are present in various lichen forms (soredia, isidia, fragmentation).
• Different modes of asexual propagation exist in lichen.

Lichen Characteristics

• Lichens are extremely diverse and have a unique morphology that differs drastically from their component parts.
• Lichens are exceptionally long-lived organisms, surviving in harsh habitats, showing great resistance to environmental stressors.
• Lichens grow slowly, from 0.1 to 10 mm a year.
• They have a long life cycle, from 4 to 8 years and up to 4500 years in some cases.

Major Lichen Types

• Ascolichens are the more common type of lichen, making up around 90% of known types.
• Basidiolichens are less common.
• The lichen partner that is a fungus (mycobiont) in 99% of the cases is an Ascomycota in the Subphylum Pezizomycotina.
• The other partner or symbiont (photobiont) is typically a green alga or a cyanobacterium.

Lichen Habitats & Ecological Roles

• Lichens are capable of thriving in extreme environments.
• Lichens play a vital role as pioneers in challenging environments.
• Lichens use a combination of chemical and mechanical processes to break down rocks and form soil.
• Lichens are sensitive bio-indicators, changing the color of the thallus in response to pollution changes.

Nutritional Advantages

• Lichens have diverse benefits due to the collaboration among organisms: protection from UV radiation and environmental stresses, as well as an increase in the ability to withstand various conditions such as heat and cold.
• Lichens exhibit remarkable tolerance to environmental factors through adaptations to harsh conditions.
• Lichens can capture atmospheric nitrogen through the interaction of the algal or cyanobacterial partner and the fungus.
• Lichens are capable of accumulating nutrients from the air.

Secondary Metabolites

• Lichens produce over 1000 secondary metabolites, many of which are not found in other organisms.
• These metabolites play diverse ecological roles.
• They protect lichens from ultraviolet radiation, pollutants, and harsh temperatures.
• They serve as a defense against pests and pathogens.

Lichen Symbiotic Partners

• Lichens can have diverse photobiont compositions (algae and cyanobacteria).
• Environmental Factors influence lichen's partners, and thus its development and diversity.
• Lichens are typically classified based on the fungus partner types.

Lichen Reproduction

• Lichens have several strategies for asexual multiplication (soredia, isidia, fragmentation).
• Reproduction in lichens can be both sexual and asexual.
• Sexual reproduction typically occurs through the formation of spores.

Lichen Structure

• There are different key structures depending on lichen type.
• Lichens have a crustose, foliose and fruticose shape.

Lichen Importance

• Lichens are important for various ecological and economical reasons and play vital roles in environments and ecosystems.
• They exhibit remarkable survivability and resilience by adapting to extreme and challenging environmental conditions.