Arbuscular mycorrhiza

Mycorrhiza-definition, Types, VAM, Symbiotic development mechanism between AM fungi and host root, pre-, early- and mature- symbiotic phases, Myc factors, Appresorium and arbuscule development, nutrient exchange

1. MYCORRHIZA, TYPES, DEVELOPMENT OF SYMBIOSIS PRESENTED BY: NEHA SHARMA Punjab Agricultural University

2. INTRODUCTION Myco - fungi, rhiza - root Coined by Frank (1885) Structure developed as a result of symbiotic association between fungi and higher plant roots. Can be in stems (e.g. orchids)

3. Fungi spreads as- EXTRARADICAL MYCELIUM grow inside the soil for nourishment INTRARADICAL MYCELIUM grow in between and inside the parenchyma cells of plant roots. forms structures- vesicles, arbuscules .

4. TYPES ECTOMYCORRHIZA ECTENDOMYCORRHIZA ERICOID MYCORRHIZA ARBUTOID MYCORRHIZA MONOTROPOID MYCORRHIZA ORCHIDACEOUS MYCORRHIZA VA MYCORRHIZA

5. 1. ECTOMYCORRHIZA mainly Basidiomycota . e.g.- Amanita muscaria , Boletus, Scleroderma citrinum Plant type- Pinus , Poplar, Oak, Eucalyptus. exists in temperate, semi-arid regions. Nutrients absorbed by the fungal mantle are transported to roots through Hartig’s net. Y-shaped rootlets- visible feature.

6. 2. ECTENDOMYCORRHIZA ECTO like- mantle + Hartig’s net (reduced) ENDO like – intracellular penetration Plant type- Pinus (pines), Picea (spruce) Fungi type- Ascomycetes ( Wilcoxina )

7. 3. ERICOID MYCORRHIZA Fungi type- Ascomycetes ( Rhizoscyphus , Sebacina ) Plant type- family Ericaceae , tribe Ericoidae Form intracellular hyphal coils The fungus digests polypeptides saprotrophically and passes absorbed nitrogen to the host plant

8. 4. ARBUTOID MYCORRHIZA Transition between ecto - and endo-mycorrhiza Fungi type- Basidiomycetes ( Boletus, Scleroderma ) Plant type- family Ericaceae , tribe Arbutoidae , genera Arbutus Feature- intracellular coils in outer cortical cells alongwith mantle and Hartig’s net

9. 5. ORCHID MYCORRHIZA Fungi type- Basidiomycetes ( Rhizocotonia solani , Sesbania , Russula ) Plant type- orchids Forms internal coils Orchid seedling is achlorophyllous , so, depends on the fungal partner for utlizing complex carbon sources.

10. 6. MONOTROPA MYCORRHIZA Plant type- achlorophyllous , Family Monotropaceae ( Monotropa hypopitys ) Fungi type- Arbustus , Pyrola depend on fungi for carbon and energy Neighbouring plants- beech, oak, spruce, pine Carbohydrates pass from conifer to Monotropa via their common mycorrhizal partner. Sheath + Hartig’s net, limited hyphal penetration into epidermal cells.

11. 7. VA MYCORRHIZA most widespread (70-90%) Fungi type- phylum Glomeromycota , 7 genera- Acaulospora , Gigaspora , Glomus , Sclerocystis , Scutellospora , Entrophospora , Gerdemannia aseptate , forms intracellular hyphae in cortex 2 structures Arbuscules - transfer mineral nutrients from fungi transfer sugars from host to fungi ii. Vesicles - storage organ of P as phospholipids

12. DEVELOPMENT OF MYCORRHIZA-HOST ROOT SYMBIOSIS A programmed sequence of phenotypic changes, due to specific recognition between the two partners- host plant and fungal symbiont . Involves 2 stages- Asymbiotic stage Symbiotic stage

13. I. ASYMBIOTIC STAGE Exist as multi-nucleated round shaped resting spores. Fungi uses its triglyceride, glycogen reserves. Under suitable water, temp. conditions- Spores germinate & nuclei from the spore move into the extending mycelium. If host root absent- growth ceases (2-4 weeks)

14. II. SYMBIOTIC STAGE Begins with the colonization of hyphae with compatible root. After attachment- Appresorium formed (fungus enters in cortex). Formation of specialized structures- inter- & intra- cellular hyphae, coils, arbuscules .

15. SYMBIOTIC PHASE

16. (A) PRE-SYMBIOTIC PHASE I. RESPONSE OF AM FUNGI TO PLANT DERIVED SIGNALS Strigolactones - short lived compound, forms a conc. gradient, stimulates spore germination. 5-deoxy-strigol: identified by fungi, leads to- Induction of branching Enhanced fungal growth Increased mitochondrial activity

17. II. RESPONSE OF PLANT TO FUNGI DERIVED SIGNALS Myc factors- soluble, fungus signalling molecule. In plants- Induces transcriptional activation of plant symbiosis related genes. Induce Ca oscillations in root epidermal cells- with the binding of LysM domain of NAG. When LysM binds to chitin perception system of root cells, induces Ca oscillations of lower frequency.

18. (B). EARLY SYMBIOTIC PHASE I. APPRESORIUM DEVELOPMENT Appresorium - A flattened, hyphal organ that facilitates the penetration of cells or tissues of other organisms. AM fungi forms a special type of appresoria called as hyphopodia , developed from mature hyphae. Formation – 1 st morphological sign due to successful pre-symbiotic recognition events.

19. II. PENETRATION OF AM FUNGI Due to sequential chemical and mechanical stimulation, plant cells produce a PPA. Fungal hypha enters the PPA, guides the fungus through root cells towards the cortex. In inner cortex, the fungus leaves the plant cell, enters the apoplast , branches and grows laterally along the root axis.

20. (C). MATURE SYMBIOTIC PHASE 1. ARBUSCULE DEVELOPMENT Hyphae induce the development of PPA-like structures in inner cortical cells, enter the inner cortical cells and branch to form arbuscules . Vesicles, function as storage organs of the fungus. New spores are typically synthesized outside of the plant root at the leading tip of individual fungal hyphae.

21. overview

22. II. SYMBIOTIC INTERFACE AND NUTRIENT TRANSFER

23. THANKS