Mycorrhiza Vam and Am type and it's physiological and Ecological studies.pptx

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1. PHYSIOLOGICAL AND ECOLOGICAL STUDIES IN MYCORRHIZA (AM and VAM) BY ISHA KEDIA CLASS ROLL NO. 416

2. INTRODUCTION : Mycorrhizae are a symbiotic association between plant roots and fungi.
Supporting plants under biotic or abiotic stress. Mycorrhiza including vesicular Arbuscular Mycorrhiza and arbuscular Mycorrhiza, ectomycorrhizal, ericoid mycorrhiza and orchid mycorrhiza. A coarse, intercellular, aseptate , coenocytic mycelium within the root tissues may develop large balloon-shaped intercalary or terminal thick walled vesicles which are multinucleate and contain large amount of lipids. Vesicles of Glomus species

3. continue… Hphae penetrating host cells fork repeatedly form richly branched arbuscules (Roots of Paris). Janse (1897) called the intramatric spores “ vesicules ” and Gallaud (1905)determined that other structures, named “ arbuscules ”. Thus the name “vesicular- arbuscular mycorrhiza”. The recognition that not all fungi formed vesicles led to the proposal that this symbiosis should be renamed arbuscular mycorrhiza. Members of the Glomineae (such as Glomus , Acaulospora ) form intraradical vesicles (VAM type), whilst members of the Gigasporineae have no intraradical vesicle (AM type). Mature Arum-type arbuscule of Glomus mosseae Paris-type intracellular coils of Glomus intraradices

4. Physiological Studies (A) Colonization of Roots: Glomus and Acaulospora colonized root from 3 inoculum sources (spores, fresh root fragments with adhering hyphae and hyphal fragments) Scutellospora and Gigaspora appear to depend entirely on spores. Spores (large thick resistant wall and numerous nuclei and are long term survival structure) with some capacity to disperal to wind and water and also animals. Germination of spores : Presence of root excudates ( Sesquiterepene , flavonoids) stimulate the growth and branching of the mycelium and apparently converting it into “infection ready” state. Germination of Glomus clarum

5. Continue…. Root fragments can be an important source of inoculum in many soils. Reports suggest they can survive in dry soil for 6 months. While infectivity is not related to presence of Vesicles. But Vesicles itself act as propagules or supports the regrowth of intercellular hyphae. Hyphal networks in soil linked to established plants are of Key importance in the colonization of seedlings in perennial vegetation systems, Hyphal networks

6. Establishment of Colonization: (A) Precolonization events. AM colonization of roots can be initiated from hyphae growing from any of the three sources of inoculum. The main hyphae approaching a root branches profusely and give to a characteristic fan-shaped complex of lateral branches Development of a densely branched hyphal network on the surface of the membrane immediately over the roots of host, but not non-host plants. (B) Contact and Penetration: Hyphal contact with the root is usually followed by adhesion of the hypha to the root surface and, after about 2–3 days, the formation of swollen appressoria , followed by root penetration and formation of arbuscular around 2 days later. Appressoria of Glomus species External hyphae and appressoria of Glomus species

7. Continue … (C) Development of Infection units. Once inside the parenchyma, the fungus forms highly branched structures for nutrient exchange with the plant called arbuscules . There are two forms: Paris type is characterized by the growth of hyphae from one cell to the next; and Arum type is characterized by the growth of hyphae in the space between plant cells. Formation of Vesicles: As individual infection units of all types age, thick-walled vesicles may be formed, depending in part on the identity of the fungus; members of the Gigasporaceae ( Scutellospora and Gigaspora ) never develop vesicles, but instead produce auxiliary Cells on the extraradical mycelium. Young arbuscule (red) Cell wall (grey) Plant cytoplasm (orange) periarbuscular membrane (light grey) Plant cell nucleus (blue)

8. (2) TRANSFER OF NUTRITION BETWEEN PLANT AND FUNGUS Membrane transport of most metabolites can be expected to be pH-dependent and to be powered by the activity of plant (1) and fungal (2) H+ - ATPases . Sucrose from the phloem is either cleaved by apoplastic invertases and taken up by the plant (3) or fungal hexose transporters or imported into root cortical cells and cleaved there by a cytoplasmic sucrose synthase (4). The fungus transforms hexoses rapidly into trehalose , which is either metabolized by the pentose phosphate pathway, or used for the biosynthesis of glycogen and lipids.

9. Continue… Fungal cell Plant cell Apoplast 4. These compounds are then exported to fungal vesicles or to the external mycelium. The plant cell takes up phosphate from the periarbuscular space using specific, H+ -dependent plant phosphate transporters (5). 5. Regarding nitrogen supply, AM-induced plant nitrate transporters (6) have been found, suggesting a similar transport mechanism as referring to phosphate. On the other hand, the observation of increased transcript levels of a fungal nitrate reductase (7) suggests the transfer of nitrogen in a reduced form (as ammonium or in an
organic form).

10. Ecological studies: The supply of phosphate ( H2PO4 depending on soil pH) is often a limiting factor to plants growing in natural soils. It is usually present in low concentrations and diffuses through soil very slowly. Its influx may increase 3 to 4-fold in infected plant roots but here are also significant increases in other minerals such as Zn, Cu, and ammonium. The water relations and resistance of infected plants to infections by pathogens may also be improved. Increased uptake of minerals is largely due to the exploration of larger volumes of soil by the extramatrical hyphae which can extend beyond the depletion zone surrounding plant roots. In nutrient-deficient soils such as sand dunes, recently disturbed soil, spoil heaps, areas covered by volcanic ash, etc., successful colonization by plants appears to be correlated with root infection by Glomales (Allen, 1991).

11. Continue . …. The roots of different plant species making up the community are in close contact and may also be connected by a hyphal network (Newman,1988). There is experimental evidence using isotopically labelled 15N, 32P, and 14C that there may be an interchange of mineral nutrients and carbon between unrelated plant species mediated by VAM mycelia, but Newman (1988) has cautioned against the conclusion that any increases in labelled materials necessarily imply net gains to receiver plants at the expense of donors . Plants forming AM network

12. Reference: Smith S.E. and Read D.J. (1983) Mycorrhizal Symbiosis. Academic Press, London Van der Heijden M. G. et al (2015) Mycorrhizal Ecology and Evolution: The past, the present and the future , New Phytologist . Koide R.T. , Mosse . B. (2004) A history of research on arbuscular mycorrhiza. Springer Webster . J , Weber . R. W. (2007) Introduction to fungi . Cambridge 218-20 Hause B. , Fester T. (2004) Molecular and cell biology of arbuscular mycorrhizal symbiosis. Springer https://en.m.wikipedia.org/wiki/Arbuscular_mycorrhiza

13. Thank you !