Mycorrhizal fungi form symbiotic relationships with plant roots where they facilitate the uptake of nutrients like phosphorus and nitrogen from the soil and transfer them to the plant in exchange for photosynthetic carbon compounds. Root exudates also play a role in nutrient absorption. Plants secrete organic compounds and ions from their roots which acidify or alkalize the soil environment to solubilize nutrients and attract beneficial microbes that aid in mineral uptake. These symbiotic relationships between plants, mycorrhizal fungi, and microbes form the basis for efficient mineral nutrition in plants.

2. THE ROLE OF MYCORRHIZAE
AND ROOT EXUDATES IN
PLANT NUTRITION.

3. AaaAAs

4. Mycorrhizae:
• In mycorrhizal SYMBIOSIS fungus provides to the host plant with
nutrients, such as phosphate and nitrogen,and increases the abiotic
(drought, salinity, heavy metals) and biotic (root pathogens) stress
resistance of the host.
• In return,it gets photosynthetically fixed carbon from the host.

5. Root exudates;
• Growing roots release an appreciable amount of
organic carbon in to rhizosphere.such as sugars and
organic acids.

6. TYPES OF MYCORRHIZA;
1. ECTO MYCORRHIZA; The fungus forms a sheath around the
rootlets and also enters roots,forming in the outer cortex,and also
form as an inter cellular net of hyphae.(harting net)
2. ENDO MYCORRHIZA; the fungus forms finely devided haustorical
branches inside the cells of root cortex.

10. Arbuscular mycorrhizal interactions;
Arbuscular mycorrhizas are the most common form of
mycorrhizal interactions. They are formed by a wide
variety of host plants (approximately 65% of all known
land plant species) including many agricultural
important crop species, such as soybean, corn, rice, and
wheat.

11. •. Structural characteristics of arbuscular
mycorrhizae
• AM fungi are obligate biotrophs and rely on their autotrophic host to
complete their life cycle and to produce the next generation of spores. The
spores are able to germinate without the presence of a host, but the spores
respond with an increase in hyphal branching and metabolic activity to root
exudates.

12. • AM fungi are coenocytic hyphae
• The polymorphic nature of these nuclei and the relatively large
genome of these fungi has made genome sequencing , but recently the
first transcriptome of the AM fungus Glomus intraradices became
available.
• They are asexual, but an exchange of genetic material between closely
related fungi via anastomosis has been observed.

13. • On the host root surface, AM fungi form a specific
appressorium – the hyphopodium.
• Fungal hyphae emerging from this hyphopodium penetrate
into the root through the prepenetration apparatus, which
guides the fungal hyphae through the root cells toward the
cortex.

14. In the cortex the hyphae enter the apoplast, and grow laterally
along the root axis, and penetrate into inner root cortical cells.
The fungus does not enter the plant symplast and is
excluded from the host cytoplasm by the enlarged periarbuscular
membrane (PAM) of the host. Some fungi also form vesicles, fungal
storage organs in the root apoplast.

15. • The mycelium that is formed within the root, the intraradical
mycelium (IRM) differs morphologically and functionally from the
extraradical mycelium (ERM), the mycelium that grows into the soil.
• The ERM absorbs nutrients from the soil and transfers these nutrients
to the host root.
• The IRM on the other hand releases nutrients into the interfacial
apoplast and exchanges them against carbon from the host.

16. • Mycorrhizal plants can take up nutrients from the soil via two
pathways: the ‘plant pathway’ that involves the direct uptake
of nutrients from the soil by the root epidermis and its root
hairs.
• the ‘mycorrhizal pathway’ that involves the uptake of
nutrients via the ERM of the fungus and the transport to the
Hartig net in ECM interactions or to the IRM in AM
interactions, and the uptake by the plant from the interfacial
apoplast.

18. ROLE OF MYCORRHIZAE IN PLANT
NUTRITION:
• MYCORRHIZAE absorbs P and N from the soil by ERM and it
transports to the IRM.
• From IRM the nutrients transported to host plant.
• There by the plants utilise these nutrients.
• In return the plants supplies carbon source to the fungi.

19. • ERM mycelium absorbs the N in inorganic form NH4
+ NO3
-
• ERM absorbs P as ortho phosphate.
• These inorganic nutrients converted into organic nutriens in the fungal
hyphae.
• The plant takes nutrients in the organic form.

20. • CONCLUSION:
• Comparing with non-mycorrhizal plants,mycorrhizal plants shows
more biomass.
• Beacause the availability of nutrients increases at root zone.
• Helps in improved plant growth and developments, and enhanced
plant tolerance to several diseases.

21. Root exudates
• Plant roots continuously exude compounds into the rhizosphere;
• this includes exudation or secretion of ions, free oxygen and water,enzymes,
mucilage and a diverse array of carbon containing primary and secondary
metabolites

22. Root exudates are often divided into two different types of
compounds:
1. Low molecular weight compounds such as amino acids, organic acids, sugars, phenolics
and other secondary metabolites which account for much of the diversity of root exudates
(ROUGIER, 1981).
2. High molecular weight exudates such as mucilage (polysaccharides)and proteins are less
diverse but often comprise to a large proportion of the root exudates

23. Enhancement of nutrient supply by root exudate
effects on symbiotic microbes
• The components of plant root exudates are complex and serve not
only as a source of carbon substrate for microbial growth, but also
chemical molecules that promote chemotaxis of soil microbes to the
rhizosphere.
• the root exudates of N2-fixing legumes are known generally for their
capacity to attract micro-organisms into the rhizosphere. Besides
their direct effects on rhizobia, root exudates can also attract
pathogenic microbes and promote the growth of plants.

24. Conclusions
• Through diverse mechanisms, root exudates play a fundamental role
in the mineral nutrition of plants. They either contain signals that act
as regulators of microbial growth and function, or they possess
molecules which directly control the rhizosphere processes that
enhance nutrient uptake and assimilation.

26. • Root excretion of inorganic ions (e.g. HCO3
−, OH−, H+) is also important in the mineral nutrition of plants. Plant uptake of anions in
excess of cations often causes the roots to secrete HCO3
− in order to maintain electrical neutrality, a process that leads to
increased rhizosphere pH. Conversely, the uptake of cations in excess of anions can cause roots to exude H+ and lower the
rhizosphere pH. The change in pH with HCO3
− extrusion tends to increase nutrient sup-ply in acidic soils, as happens with H+
exudation in calcareous soils.
•
• H+ extrusion is largely governed by cation/anion balance and is thus very much influenced by the N source. Plants growing on
nitrate generally maintain electronic neutrality by releasing excess anions, in-cluding OH−, which cause an increase in rhizosphere
pH and an enhanced nutrient (P, Mo, etc.) availabil-ity in acidic soils (Marschner, 1995). An exception is the study by Gahoonia et
al. (1992) which showed no effect on P mobilization in a luvisol soil following nitrate-induced increase in rhizosphere pH. However,
when ammonium is supplied, there is a large excess of cations and a resulting enhanced H+ extrusion and rhizosphere acidification,
thereby making P, Mn, Fe, Cu and Zn more toxic in the acidic range, or readily available in the alkaline range (Aguilar and Van Diest,
1981; Gahoonia et al., 1992; Gardner et al., 1983; Gillespie and Pope, 1990; Runge and Rode, 1991). Sometimes, however,
acidification from ammonium nutrition does not result in increased P mobilization, especially in acidic oxisols (Gahoonia et al.,
1992). Furthermore, H+ extrusion occurs during N2 fixation by symbiotic legumes (Raven et al., 1990), and this can lead to
rhizosphere acidification and increased availability of limiting nutrient elements like P, Mo and Fe (Aguilar and Van Diest, 1981;
Gahoonia et al., 1992; Gillespie and Pope, 1990; Runge and Rode, 1991) which are much needed in diazotrophy. Ad-ditionally,
there are many reports of enhanced H+ extrusion under Fe defiency and P deficiency, both leading to acidification of localized
areas around the root tips (Bienfait, 1985, 1988; Gardner et al., 1983; Hoffland et al., 1989; Römheld and Marschner, 1986) and a
consequent improvement in the availability of

27. • Root exudate effects on rhizosphere pH and nutrient availability
•
• Another nutritional effect that organic acids have in root exudates is acidification of
the rhizosphere. Root exudation of high concentrations of organic acid anions as a
result of P deficiency does lower rhizosphere pH, making P and micronutrients such as
Mn, Fe and Zn to be more available in cal-careous soils.
• However, the relationship between organic acid exudation and rhizo-sphere
acidification is not that simple as the extrusion of H+ would depend on the amounts of
anions ab-sorbed by roots relative to cations. Whatever the case, acidific-ation below
pH 5.5 can cause even major macronutri-ents to become limiting. Because
micronutrients such as Mn, Fe and Al occur in high concentrations below pH 5.5 any
further acidification
• by organic acids below this level can result in phyto-toxic effects on plant roots and
beneficial microbes. Intriguingly, the white lupin can mobilize P from both acid and
alkaline soils by using citric acid in its pro-teoid root exudates to acidify even the
alkaline soil, and thus solubilize P as well as Fe, Mn, Cu and Zn for uptake by roots.