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Root microbe interactions,types of Mycorrhizae

The document discusses root microbe interactions, including both beneficial and pathogenic associations with plants, and highlights the importance of the rhizosphere and the role of mycorrhizae in plant nutrient uptake. Mycorrhizae establish mutual relationships between plant roots and fungi, with two main types: ectomycorrhizae and endomycorrhizae, each characterized by distinct structural and functional interactions. Ectomycorrhizae typically develop on woody plants, while endomycorrhizae penetrate plant cells, allowing for complex nutrient exchange mechanisms.

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ROOT MICROBE INTERACTIONS
• Root microbe associations are quite complex and may involve invasion of the host root by the organism. • Microorganisms may remain free living in the soil. Sometimes the association may prove beneficial to the plant or it may be pathogenic and cause injury. • These microorganisms play a significant role in the inorganic nutrition of plants.
• The rhizosphere is the narrow region of soil or substrate that is directly influenced by root secretions and associated soil microorganisms known as the root microbiome. • Soil pores in the rhizosphere can contain many bacteria and other microorganisms that feed on sloughed-off plant cells, termed rhizodeposition, and the proteins and sugars released by roots, termed root exudates. • This symbiosis leads to more complex interactions, influencing plant growth and competition for resources. • Soil bacteria can assist in making phosphorus available to the plant.
Mycorrhizae • Mycorrhizae literally translates to “fungus-root.” • Mycorrhiza defines a mutually beneficial relationship between the root of a plant and a fungus that colonizes the plant root. • In many plants, mycorrhiza are fungi that grow inside the plant’s roots, or on the surfaces of the roots. • The plant and the fungus have a mutually beneficial relationship, where the fungus facilitates water and nutrient uptake in the plant, and the plant provides food and nutrients created by photosynthesis to the fungus. • Not all plants will have mycorrhizal associations.
Types of Mycorrhizae: • The two main types of mycorrhizae are ectomycorrhizae and endomycorrhizae. They are categorised according to where the fungi colonise on the plants. • ECTOMICORRHIZAE: • Ectomycorrhiza, also known as EcM, usually develops connections between woody plants (like beech, birch, willow, oak, pine, fir and spruce) and fungi belonging to the Ascomycota, Basidiomycota, and Zygomycota. • Ectomycorrhizae (‘’outer fungus root’’) are common and wrap fungal threads around the root tip in a hyphal sheath or mantle. • Hyphae also penetrate the root cortex (outer layer) between but outside root cells, in what is called a Hartig net.
ENDOMYCORRHIZAE: • Endomycorrhizal relationships are characterized by a penetration of the cortical cells by the fungi and the formation of arbuscules and vesicles by the fungi. • In other words, endomycorrhiza have an exchange mechanism on the inside of the root, with the fungi’s hyphae extending outside of the root. • ENDOMYCORRHIZAE are further subdivided into specific types: Arbuscular Mycorrhizae, Ericaceous Mycorrhizae, Arbutoid Mycorrhizae, and Orchidaceous Mycorrhizae.
• Vasicular-Arbuscular Mycorrhizae (VAM) • This type of Mycorrhizae is most commonly found in the majority of the world’s vegetation. • Vasicular-Arbuscular mycorrhiza (VAM) is formed by the symbiotic association between certain phycomycetous fungi and angiosperm roots. • The fungus colonizes the root cortex forming a mycelial network and characteristic vesicles (bladder-like structures) and arbuscules (branched finger-like hyphae). • The arbuscules are the most characteristic structures, formed intracellularly and probably having an absorptive function. • The vesicles are terminal swellings of hyphae formed inter and intracellularly having a storage function.
Nutrients move from the Mycorrhizal fungi to the root cells: • In ectomycorrhizae , inorganic phosphate may simply diffuse from the hyphae in the hartig net and be absorbed by the root cortical cells. • In vasicular arbuscular Mycorrhizae,the situation may be more complex to nutrients may diffuse from intact arbuscules to root cortical cells. • Deficiency of nutrients may tend to promote infection,where as plants under a good supply of nutrients tend to suppress infection.