Fungal Symbiosis (Lichens and Mycorrhizae) By : Thabat Khatib Presented for: Dr. Ghadeer Omar

What is Symbiosis ? Symbioses are intimate associations involving two or more species (often long-term interaction). In the natural world no organism exists in absolute isolation, and thus every organism must interact with the environment and other organisms.

Classification of Symbiosis Symbiosis can be classified into different categories: Dependent on each other for survival. Physical attachment of the organisms. Physical interaction. Biological interaction.

Dependent on each other for survival Symbiosis Obligate Facultative Both symbionts entirely depend on each other for survival They can, but do not have to live with the other organism

Physical attachment of the organisms Symbiosis conjunctive symbiosis disjunctive symbiosis The organisms have bodily union The organisms are not in union

Physical interaction Symbiosis Endosymbiosis Exosymbiosis The symbiont lives on the body surface of the host, including the inner surface of the digestive tract One symbiont lives within the tissues of the other, either within the cells or extracellularly

Biological interaction Symbiosis Mutualism Parasitism Commensalism Both organisms benefit in a symbiotic relationship One of the organisms benefits, where the other one is harmed One of the organisms benefits, where the other is unaffected

With algae and cyanobacteria Fungal Symbiosis Many fungi have important symbiotic relationships with organisms from most if not all Kingdoms. Fungi Symbiosis With insects With plants With algae and cyanobacteria

Importance of Fungal Symbiosis The main physiological basis for this symbiosis is bidirectional nutrient transfer. The ability of symbiotic partners to tolerate environmental stress and inhabit environments that they could not live in individually.

Fungi-Plant Symbiosis (Mycorrhiza) A mycorrhiza is defined as a symbiotic relationship between the roots of plants and fungi. Includes plants that do not have roots, such as bryophytes (mosses and liverworts).

Characteristics of Mycorrhizae Enhances mineral transport to plants, especially phosphorous. Infection occurs only at root tips. Relationships obligate and facultative. Plants with mycorrhizae more drought resistant. Plants with mycorrhizae more resistant to plant pathogens.

What happens in Mycorrhizae ? Fungi: invades tree roots and obtains nourishment by tapping into the plant’s vascular system. Plant: increasing the plant’s access to water and relatively immobile nutrients (greater uptake of mineral ions such as nitrogen, potassium and particularly phosphorus) and protection of its roots against pathogens.

Categories of Mycorrhizae Two Major Categories: Ectomycorrhizae Mycelium forms an external sheath around root tip. Does not penetrate cells of root. Endomycorrhizae Mycelium does not form sheath and does penetrate root cells

Ectomycorrhizae Fungus groups involved are mostly mushrooms and related groups with large fruiting bodies, e.g. mushrooms, truffles and puffballs. Fungus receives carbohydrate from plant and plant has enhanced mineral uptake.

Ectomycorrhizae Mycelium forms only around the root tips, forming an external sheath around root. Fungus penetrates epidermis and grows between root cells in cortex. Fungus does not penetrate cells of root.

Normal Uninfected Root Root Cortex Epidermis

Infected Ectomycorrhizal Root Mycelial Sheath Intracellular mycelial Growth

The infected roots are very distinctive, forming short, paired, branches (induces root tips to branch, dichotomously).

Endomycorrhizae Most mycorrhizal fungi in this group. The sheath is reduced or absent. Occurs in almost all groups of plants. Endomycorrhizae inconspicuous due to lack of large fruiting body

How does it Occur ? For a hypha to enter into a root, it adheres by the formation of a swollen structure called appressorium. This appears to be formed as a result of topographical or biochemical signals. Following adhesion, the colonization of the root cortex occurs.

Categories of Endomycorrhizae Arbuscular mycorrhizae Orchid Endomycorrhizae Ericaceous Endomycorrhizae

1) Arbuscular mycorrhizae Vesicular-Arbuscular Mycorrhizae (VAM). Now Arbuscular mycorrhizae . The name comes from the distinct structures that can be seen inside the cells of the infected roots, the rounded vesicles and the branched tree-like arbuscules.

Vesicles and Arbuscules of VAM Fungus

AM Endomycorrhizae Vesicles and arbuscules within cells are lysed by host-root cells where the stored minerals needed by plant is stored. Identified by the large spores that are produced in the soil. Spores are just visible to the naked eye.

Round, yellow-orange structures are VAM spores Spores of VAM Fungus Round, yellow-orange structures are VAM spores

VAM Spores Under Microscope

Relevance of VAM Many native Hawaiian plants’ seeds cannot be germinated and if germinated do not readily grow.

2) Orchid Endomycorrhizae Orchid, if not photosynthetic, derives carbohydrate from fungus, until it is able to produce its own food. Even then, it is still dependent upon fungus for minerals.

3) Ericaceous Endomycorrhizae Classified into two main groups Ericoid Mycorrhizae Monotropoid Mycorrhizae Found with plants in stress environment and requires fungus to grow normally Found with non-chlorophylls parts of some plants.

Lichens Mycobiont Photobiont Lichen is an intimate, symbiotic association of a tangled mass of fungal hyphae that holds a photosynthetic green or a blue-green partner a stable thallus of specific structure

Symbiotic Relationship Fungi Algae Cyanobacteria Symbiotic Relationship

Importance of Lichens Lichens can survive in the most extreme and severe environments where neither plants nor fungi can exist alone. Lichens can also tolerate heat that would desiccate and kill most plants. Antibiotics have been extracted from lichens. Some lichens used as a source of food. Most species of lichens are extremely sensitive to sulfur dioxide in the air and are therefore indicators of air pollution.

Do lichens represent a true mutualistic type of symbiosis? One of the most basic questions, that has been asked since the discovery of the lichen symbiosis, concerns whether lichens represent a true mutualistic symbiosis or nothing more than a variation of a host-parasite relationship.

The Lichen Thallus Foliose Fruticose Squamulose Crustose A thallus, which is leaf-like, and attached to the substrate at various points A thallus, which is made up of pendulous branches. Attached at a single point A thallus, which is flattened against the substrate and its lower surface entirely attached A thallus, which starts off like a foliose lichen, then develops branches called podetia

Foliose Lichen

Section of Foliose Thallus Upper Cortex: Tightly woven mycelial layer. Algal Layer: Algal Cells and mycelium. Medullary Layer: Loosely interwoven mycelium. Lower Cortex: Tightly woven mycelial layer. Rhizines: Outgrowth of lower cortex that attaches to substrate .

Section of Foliose Thallus

Crustose thallus Crustose thallus: Flattened against substrate, attached by medulla. Often looks like a painted surface.

Section of Crustose Lichen

Fruticose Lichen Fruticose thallus: Often stringy in appearance and attached at a single point. Commonly found hanging on trees.

Section of Fruticose Lichen

Squamulose lichens Lichen Podetia

Section of Squamulose lichens Some lichens have a portion of their thallus lifted off the substrate to form 'squamules

Leprose Lichens (Rare form) Leprose lichens are an odd group of lichens

Reproduction of Lichens Soredia: fragments of algal layer that is dispersed through a rupture in upper cortex. Each soredium can give rise to a lichen.

Fungal Symbiosis With Insects The fungus grows a tough cover over the colony of scale insects or arthropods. The fungus also penetrates insects through natural openings forming haustoria . Insects continue to feed, providing a flow of nutrients to the fungus directly from the plant

Haustorium The appendage or portion of a parasitic fungus (the hyphal tip) or of the root of a parasitic plant that penetrates the host's tissue and draws nutrients from it

Many insects have a symbiotic relationship with certain types of fungi: Termites: When termites have eaten a big meal of wood or leaves, they also eat some fungi from their gardens. The fungi help them digest the wood or leaves. Leafcutter ants: grow fungi on beds of leaves in their nests. The fungi get a protected place to live. The ants feed the fungi to their larvae. Ambrosia beetles: live in the bark of trees. Like ants and termites, they grow fungi inside the bark of trees and use it to help digest their food.

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