Soil, Plant, microorganism are interrelated and interdepended. Among the microorganism Mycorrhizae is an important one. this presentation highlighted the the benefits of mycorrhizae in drought tolerance of plants.

1. Speaker: Prateem Bishnu
Bidhan Chandra Krishi viswavidyalaya
Dept. of Agronomy
Mohanpur, Nadia, 741235
“Significance of arbuscular
mycorrhizae (AM) on drought
tolerance- its effect and mechanism”

2. Drought
• A prolonged period of
abnormally low rainfall,
leading to a shortage of
water.
• A drought or drouth is
an event of prolonged
shortages in the water
supply, whether
atmospheric, surface
water or ground water.

3. Agricultural Drought
Agricultural drought
refers to circumstances
when soil moisture is
insufficient and results
in the lack of crop
growth and production.
It primarily concerns
itself with short term
drought situations.

4. Drought VS Food Insecurity
•India faced 22 no. of drought between 1987 to 2002.
•In 1987, worst drought faced by India causes 60 % loss of
crop field.
•Drought and food security are intimately linked.
• Rainfed crops account for 48 per cent of the total area under
food crops and 68 per cent of the area under non-food crops
(NRAA).
•Around 78 per cent of the farmers who committed suicide in
the last one decade were small farmers and 76 per cent of
them were dependent on rain-fed agriculture.

5. Estimation of loss in Agriculture
Natural Disaster Losses ( in billion during 2005 to 2015)
Drought $ 29
Flood $ 19
Landslides $ 10.5
Other meteorological disaster
(Extreme temperature , storm etc.)
$ 26.5
Biological disaster & wildfire $ 10.5
Source: http://www.fao.org/news/story/en/item/1106977/icode/

6. Plant Adoption During drought
Drought
Physiological response Molecular response
Biochemical response
• Root signal recognition at
the spot.
• Loss of turgor & osmotic
adjustment.
• Reduce transpiration rate
due to stomatal closure.
• Reduce internal Co2
concentration.
• Reduce photosynthetic
rate.
• Reduce growth.
 Decrease photochemical
efficiency.
 Decrease activity of RuBisco.
 Accumulation of metabolites like
MDHA, glutathione, proline,
glycine betane, ployamines and
α - tocophenol
 Increase in antioxidative enzyme
like SOD, CAT, APX, POD, GR
and MDHAR.
 Reduced ROS accumulation
 Stress response gene
expression.
 Increased expression of
ABA biosynthesis
expression genes.
 Synthesis of specific
protein like LEA, DSP,
RAB, dehydrin.
 Drought stress
tolerance.

8. Arbuscular Mycorrhizea
• Greek work ‘mukes’ means fungi and
‘rhiza’ means roots.
• Most common form of mycorhhizal
interaction (about 65% of cultivated
species).
• Belong to separate fungal phylum
Glomeromycota.
THREE CLASSES
1. Archaeosporomycetes,
2. Glomeromycetes, and
3. Paraglomeromycetes
THE FIVE ORDERS:
1. Archaeosporales (e.g. Geosiphon
pyriformes)
2. Diversisporales (e.g.Scutellospora
calospora)
3. Gigasporales (e.g.
Gigasporamargarita)
4. Glomerales (e.g. Glomus
intraradices) and
5. Paraglomerales (e.g. Paraglomus
occultum).

9. Fig1: Life cycle of
an AM fungus and
the different steps
during AM
development.

10. How it’s
work ?

12. Effects of AM Fungi on Host Plants
AM on host
plant
Morphology Metabolism

13. Effects On Morphology
Bildusas et al.
1986;
Bethlenfalvay et
al. 1987
AM effects on stomatal conductance have been
observed with similar frequency under amply
watered and drought conditions. In several
studies, differences between AM and NM plants
were observed only under drought, when stomatal
conductance was measured under both non-stress
and drought conditions.
Ruiz-Lozano
et al. 1995
AM-induced increases in transpiration and
stomatal conductance in non-stressed plants are
often subtle but have been found to be three times
that of P-limited NM controls

14. Effects on Morphology
Allen and
Boosalis, 1983,
Plant colonized by AM fungi can tolerate and recover more
rapidly from soil water deficits than plants without AM fungi.
Johnson and
Hummel,1985
Increased resistance to drought and transplant stress by
carrizo citrange Seedlings inoculated with glomus
intraradices as compared to un-inoculated ones.
Gemma et al.
1997
AM plants would recover from wilting more quickly than
NM plants upon relief of drought.
Henderson &
Davies, 1990
AM symbiosis has generally not affected stomatal density
and guard cell size when comparing AM and NM plants with
similar leaf areas, even when transpiration or stomatal
conductance differed

15. FIG 1: Plant growth of trifoliate orange inoculated with Diversispora versiformis (AMF) under well-watered (WW)
and drought stress (DS) Source: He et. al. (1999)

16. Effects on Morphology
Table 1 : Effect of plant growth regulators and AM on germination (%) at different levels of moisture stress in cotton
Irrigation levels/ seed
primimg treatment
Germination (%)
I1 I2 I3 Mean
T1 : GA3 (100 ppm) 96.0 71.2 54.3 73.8
T2 : CK (10 ppm) 94.3 68.2 58.8 73.8
T3: CCC (200 ppm) 95.1 78.0 65.9 79.6
T4: AM ( 5g/ Kg of soil) 97.8 84.1 77.1 86.3
T5: Control 92.0 59.0 40.8 63.9
Mean 95.0 72.1 59.4
For comparing SEm CD
Treatments (T) 0.07 0.27
Irrigation levels (I) 0.04 0.16
Interaction (T X I) 0.20 0.80
I1 : 100 % Field capacity
I2 : 70 % Field capacity
I3 : 50 % Field capacity
RUPA S. HAVARGI , 2007

17. Effects on Morphology
Table 2 : Effect of plant growth regulators and AM on total chlorophyll content (mg g-1 fresh wt.) in leaf at 45 and 65 DAS
under different levels of moisture stress in cotton
I1 : 100 % Field capacity I2 : 70 % Field capacity I3 : 50 % Field capacity
RUPA S. HAVARGI , 2007
Irrigation levels/ seed
primimg treatment
45 DAS 60 DAS
I1 I2 I3 Mean I1 I2 I3 Mean
T1 : GA3 (100 ppm) 1.52 1.33 1.14 1.33 1.64 1.47 1.28 1.46
T2 : CK (10 ppm) 1.55 1.37 1.22 1.38 1.74 1.62 1.40 1.58
T3: CCC (200 ppm) 1.70 1.51 1.24 1.48 1.90 1.71 1.53 1.71
T4: AM ( 5g/ Kg of soil) 1.79 1.61 1.38 1.59 2.05 1.77 1.62 1.81
T5: Control 1.50 1.26 0.98 1.25 1.58 1.40 1.16 1.38
Mean 1.51 1.41 1.19 1.78 1.59 1.40
For comparing SEm CD SEm CD
Treatments (T) 0.011 0.04 0.013 0.05
Irrigation levels (I) 0.007 0.02 0.008 0.03
Interaction (T X I) 0.035 0.13 0.040 0.15

18. Effects on Metabolism
METABOLISM
WATER
METABOLISM
PHOTOSYNTHESIS
GROWTH &
ABSORPTION
CAPACITY
PROTECTIVE
ADOPTATION

19. Effects on Water Metabolism
Host species Fungus species Parameter Drought Reference
Sorghum bicolor G. macrocarpus < WUE X Sieverding (1979)
Trifolium repens G. fasciculatum > WUE X Puppi & Bras (1990)
Trigonella
foenumgraecum
G. macrocarpus
< WUE X Sieverding (1979)
Triticum aestivum G. fasciculatum
> Soil water
extraction
X Ellis et al. (1985)
Acasia
auriculiformis
Two G.spp
<leaf potential, <
leaf RWC, < soil
water content, >
growth relative to
non-stressed plant
X
Osonubi et al.
(1991)
Agropyron smithii Indigenous
> Leaf water
potential
X
Allen and Allen
1986
Capsicum annuum G. deserticola
> Leaf potential, >
RWC, < wilting
X Davies et al. (1992)

20. Effects on Photosynthesis
Augé et al. 2014
Effects of AMF on actual photosynthetic rates are considered
transient and hardly predictable; measured rates of stomatal
conductance and photosynthesis are frequently not consistent
with the growth outcome.
Ögren and Evans, 1993
Under low light, photosynthesis is mainly limited by incoming
energy and, hence, by the rate of electron transport, but not
directly by its capacity
Merilo et al. 2018
Stomata close upon atmospheric drought, which limits
CO2 availability at the sites of carboxylation.
Dewar 2002; Tardieu
and Davies 1993
Plants regulate stomatal aperture under drought to avoid
excessive water loss and wilting which limits CO2 influx

21. Effects on Photosynthesis
Smith and
Read, 2008
Both direct and indirect contributions to nutrient and water
extractability from soils require that hyphae proliferate
beyond the ambit of roots which are developed with
sustenance by plant C fixed in photosynthesis
Augé et
al. 2014, 2016;
Boldt et al. 2011
Rates of photosynthesis of mycorrhizal plants are
commonly altered in comparative studies with non-
mycorrhizal (NM) counterparts
Řezáčová et
al. 2018
Mycorrhizal plants possess an additional and significant C
sink ,which can be compensated by photosynthesis,
provided that AMF do not only substitute other plant C
sinks in the symbiotic interaction

22. Effects on Growth & Absorption Capacity
Wu & Xia .,2004
AM symbiosis improved absorption capacity and
increased the growth of its host plant, which was proved in
sugarcane, mung bean, apple, orange, wheat, tomato and
wild jujube.
He et al., 1999
water content of soil was 12%,biomass of mung bean
colonized with Glomus mosseae, Glomus spp. or Glomus
caledonium were found 1.99,1.95,and 1.80 times that of
their control NM partners.
Subramanian
&Charest, 1997
In the condition of drought stress, biomass of shoot and
root in AM maize decreased by 12%,31%,while in NM
plants they decreased by 23% and 55% individually.

23. Effects on Growth & Absorption Capacity
Lambert
&Weidensaul.,
1991
Concentration of Cu and Zn in AM plants have been
suggested higher than that of NM plants in more than one
half of researches, while concentration of Mn in leaf of AM
plant was lower than that of NM one.
Augé.,2001
AM plants also appear to absorb less boron than NM plants
during drought. Shoot concentrations of nitrogen,
potassium, calcium, magnesium, iron, sodium and
molybdenum appear to be little affected by AM symbiosis in
drought conditions.
Zajicek et al.,1987
The growth of two forbs with no supplemental phosphorus
was improved by all the Glomus spp.

24. Effects On Protective Adoption
Schellenbaum
et al.,1998
In drought conditions, concentrations of amino and imino acids
in plants with AM symbiosis have been reported to increase.
Augé et
al.,1992
Levels of proline and other compounds such as free polyamine
have also been compared in AM and NM plants, as a measure
of resistance capacity or injury. The results are in consistent
with studies on soluble sugars.
Ruiz-Lozano
et al.,1996
AM and NM plants during drought and found to be typically
higher in AM plants. For example, AM lettuce had higher root
and shoot superoxide dismutase activity than NM lettuce

25. Effects on Protective Adoption
Schellenbaum
et al.,1998
AM symbiosis significantly affected tobacco plants during
drought in terms of soluble carbohydrate accumulation and
partitioning.
Davies et al.,
1993
AM plants accumulated less glucose and fructose in leaves and
roots than NM plants in drought conditions. Similar findings
were reported for rose and pepper after drought.
Subramanian
& Charest,
1995
Higher foliar concentrations of soluble sugars in AM than in NM
maize plants after drought was reported, suggesting the positive
role of AM in enhancing drought resistance of host plants.

26. Effects on Protective Adoption
Ruiz-Lozano ,
2003
AM alfalfa higher acid phosphatase activity than NM alfalfa.
Panwar, 1993
Nitrate reductase activity in leaves and roots was also
increased by AM symbiosis in numerous studies
Augé, 2001
Total protein concentrations have been consistently higher in
AM than NM plants during drought, considered by the
authors to be a beneficial AM effect

27. What is the mechanism?

28. Development of Soil Rhizosphere
• Mycorrhizal fungi can potentially influence soil aggregation at different
levels, namely:
1. Plant communities,
2. Plant roots (individual host), and
3. Effects mediated by the fungal mycelium itself.

29. Fig2: Conceptual overview of the three main different scales (plant community, individual plant,
and mycelium) at which mycorrhizal fungi can influence soil aggregation

30. Plant Roots: Individual Host Level
Effects
Five Categories
1. Root physical force/penetration.
2. Soil water regime alteration.
3. Rhizodeposition.
4. Root decomposition.
5. Root entanglement of soil particles.

31. ROOT ENTANGLEMENT AND PHYSICAL
FORCE/PENETRATION
Mycorrhizal Fungi
Root‐tip enveloping
mantle
Extensive change in
root architecture
Compressive and
shear stresses
Stress up to 2 MPa
Localized soil compression
and reorientation of clay
particles along root surfaces
MICROAGGREGATE FORMATION

32. Changed Soil Water Regime
Efficient exploration
of water
Higher stomatal
conductance and
transpiration
Better root growth
Secretion of root
exudates
Better soil aggregation
Symbiotic association
with plant
Fixed more carbon
More carbon input in to the soil
a)
b)

33. Rhizodeposition
• Release of compound from living roots, specially influenced by
AM fungi.
• Mainly representing the sizeable sink for plant derived carbon.
• Also causes the qualitative shift
Example, Root mucilage.
• Increase the other microbial activity.

34. Effects of Fungal Mycelium
BIOPHYSICAL
BIOLOGICAL
BIOCHEMICAL
SOIL
RHIZOSPHERE

35. Fig : Overview of various
mechanisms (including
hypothesized processes)
that are hyphal mediated
and influence the
formation or stabilization
of soil at macroaggregate
and microaggregate scales.

36. Table 1: Role of Fungal Mycelium in Aggregate formation
or stabilization
Mycelium Aspect Formation Role Stabilization Role
Overall hyphal
abundance protein or
exopolymer
deposition
Carbon input to nucleation sites; degree
of particle alignment association
(protein as versatile molecules at
mineral surfaces).
Degree of aggregates surficial
cover (i.e. mesh size of an
aggregate enveloping
network hydrophobicity).
Mycelium growth rate Exertion of physical force (Pressing
particles together).
Continued delivery of plant
derived carbon to aggregate
surface: rapidly bridging
planes of weakness.

37. Table 1: Role of Fungal Mycelium in Aggregate formation or stabilization
Mycelium Aspect Formation Role Stabilization Role
Mycelium
architecture
Absorptive mycelium contributes
to primary particles alignments
and enmeshment.
Runner hyphae provide ‘
backbone’ of stabilizing
network on aggregate
surface; provision of
tensile strength.
Hyphal
decomposition
Provision of nucleation sites for
microaggregate formation.
Carbon input to
aggregate surface/
surficial pores (coating).
Table 1: Role of Fungal Mycelium in Aggregate formation
or stabilization

38. Biochemical Mechanism
3 types of biochemical mechanism have been identified:
Glomalin and glomalin‐related soil protein.
Mucilages, polysaccharides and other extracellular
compounds.
Hydrophobins and related proteins.

39. Glomalin and glomalin‐related soil protein
(GRSP)
• Actually a gene product.
• Act as Glue with Hydrophobic properties.
• Tightly bond with mycelium rather than separated into the soil
(Nearly 80%).
• Primarily they have role in fungus body and secondarily act as soil
bonding agent.
• V. Gadkar & M. C. Rillig isolated glomalin form fungus showing
similar properties as stress induced protein.
• GRSP primarily reviewed as soil aggregating protein but lack of
evidence in this matter and required further research on this topic

40. Mucilages, polysaccharides and other extracellular
compounds.
• Microbes produce a variety of extracellular polymeric
compounds for several purposes, including attachment,
nutrient capture and desiccation resistance.
• Caesar‐TonThat, 2002 observed as a part of his work,
polyclonal antibodies were developed and directed at
quantifying mycelium products involved in soil
aggregation.
•Extensive qualitative and quantitative analysis of
exudates derived from different AMF species, is clearly
needed to clarify AMF roles in soil aggregation.

41. Hydrophobins and Related Proteins
• Hydrphobin is recently discovered small proteins involved
in various functions from mycelium attachment to surfaces,
alteration of biotic or abiotic surface properties, and
lowering water tension.
• Hydrophobins have not yet been described for AMF, but are
known to occur in ectomycorrhizal fungal species.
• It have a strong functional role in soil aggregation can be
hypothesized, but there is presently no evidence for this.

42. Biological mechanisms
2 types of biological mechanism have been identified:
Mycelium‐influenced microbiota.
Soil food web.

43. Mycelium‐influenced microbiota
•AMF influence soil microbial communities, how and where
within the soil matrix these changes are mediated, and the
significance of these changes to soil aggregation and other
processes, is poorly defined.
•AMF‐facilitated alteration of prokaryotic communities may
indirectly influence aggregation processes at scales smaller
than the macro aggregate.

44. Mycelium‐influenced microbiota
•First, AMF can directly influence bacterial communities via
the deposition of mycelium products that serve as substrates
for bacterial growth.
•Mansfeld‐Giese et al., 2002 found Interestingly, bacteria
(such as Paenibacillus spp.) have recently been isolated
from AMF mycelia which appear to be important in soil
aggregation.
•Additionally, AMF deposition products may also contain
bacteriostatic or fungistatic agents, a possibility suggested
by the results of Ravnskov et al.,1999.

45. Mycelium‐influenced microbiota
•Second, AMF modification of rhizodeposition products,
both quantitatively and qualitatively results in alteration of
the composition of the bacterial community.
•Third, all AMF activities, resulting in the alteration of soil
structure, influence the nature and extent of pore spaces
available for microbial habitation.

46. Biophysical Mechanisms
3 types of biochemical mechanism have been identified:
1. Enmeshment
Similarly to the action of roots, albeit at a smaller scale, hyphae
serve to enmesh and entangle soil primary particles, organic
materials and small aggregates, facilitating macroaggregate
formation, while potentially eliminating spatial constraints on
microaggregate formation.

47. 2. Alignment
Primary
particle aligned
along growing
hyphae
Hyphae act
as tunneling
machine
Pressure
adjacent soil
particle
Force clay and organic matter to
form macroaggregation

48. 3. Altered Water Relations
Wet- dry cycle in
the rhizosphere Increased binding
of root and fungal
exudates onto clay
particles
Hydrolic - lift by
mycorrhizea in
top layer

49. Nutrient Uptake

50. N Transport and Transformation
Soil Mycorrhizal Fungi Plant
NO3
- NO3
- NO3
-
NH4
+ NH4
+
NH4
+
glutamine
glutamate
glutamine
glutamate
Sucrose
glycine
glycine
CO2

51. • Arginine is usually the principal nitrogenous product
accumulated during periods of ammonium feeding at the uptake
site, providing support for the importance of this amino acid in
N transfer between fungal and plant cells.
• The extrusion of ammonia from fungal cells follows other
pathways than those mediated by Amt proteins (ammonia
transporter), either by passive efflux of the deprotonated form or
by protein-mediated mechanisms. Thus, fungal cells are able to
maintain a low cytoplasmic ammonia concentration, thus
retaining a constant assimilatory capacity and in turn allow for
sustained export into the plant root cells.
Arginine

52. AM fungi take up inorganic N (NH+4 ,NO−3 ),mostly incorporated and stored
in arginine.
Assimilation of the N through GS/GOGAT, asparagine synthase and the urea
cycle
Stored arginine can be co-transported with PolyP intact to the intraradical
mycelium form the extraradical mycelium of AM fungi, and arginine is also
bi-directionally transported within the extraradical mycelium.
N released from transported arginine is transferred to the host as NH4+ and can
be incorporated into other free amino acids in mycorrhizal roots, while carbon
(C) not transferred to the host is recycled back to the extraradical mycelium.
Jin et al. (2005),
Model of Nitrogen Transport

53. Phosphorus Transport
Highly immobile in soil and rapidly mobile in plant
Development of P depletion zone around root hair cylinder
& a rapid decline of P over time
Increase the availability of P far beyond the root zone
Rapid uptake by the plant
Association of AM fungi root mycelium
• Phosphorus is transported to the plant by means of organic form Polyphosphates from AM
fungus soil interface to the intraradical symbiotic interface (Bucher, 2007).

55. Water Absorption

56. Water Absorbtion
•The important parameter for effective water movement
through plant from water is,
1. Stomatal conductance
2. Hydraulic conductivity
3. Transpiration rate
4. Leaf water potential
Symbiotic relation of plant with AM Fungi improve or
maintain above parameters during drought.

57. Hydraulic conductivity in extraradical hyphae and roots
Augé et al., 2008 The possible mechanisms for tolerance
improvement of mycorrhizal plants to water
deficit could be related to the increase in
hydraulic conductivity of roots
Augé, 2001 ;
Meddich et al.,
2015
A larger root system due to AMF hyphae that
increase the exploration area in soil, which has a
direct effect on the relative water content
(RWC), water potential, transpiration rate, and
crop yield.

58. Hydraulic conductivity in extraradical hyphae and roots
Marulanda et al.,
2003; Wu et al.,
2008
Living hyphae that are involved in water transport
possess a diameter between 2 and 5 and can penetrate
smaller soil pores that are inaccessible to root hairs (10
to 20 diameter) and thereby absorb water. In addition,
AMF have demonstrated a beneficial effect on soil
structures, specifically generating stable aggregates due
to the production of a glycoprotein known as Glomalin.
Augé et al., 2007 As a consequence, soil colonization may be as
important as root colonization in the AMF effect on
water relationship in host plants.

59. STOMATAL CONDUCTANCE
Augé et al., 2015
The existence of variations in the stomatal conductance
during water deficit periods has been demonstrated although
the effect of AMF is not always apparent and is unpredictable
Wu and Xia,
2006
In mycorrhizal plants, such as rosemary, tangerine and rice
under water deficit and inoculated with AMF, an increase in
the stomatal conductance has been observed.
Benabdellah et
al., 2011
white clover have displayed a decrease in stomatal
conductance and an increase in the RWC in the same
conditions, both associated with a more water use efficiency.

60. Xie et al. 2018
Movement of water happens by a gradient-driven flow through
membranes, a process which is regulated and mediated by water
channels called aquaporins (AQPs)
Marjanović et al.
2018
Plant AQPs play a key role in AM symbiosis and might respond
differently to subjected drought stress and AMF colonization
Li et al. 2013
the expression of two AQP genes GintAQPF1 and GintAQPF2 was
significantly enhanced, in extraradical mycelia of R. irregularis and
mycorrhizal roots in response to drought stress, thus supporting the
existence of a direct AMF involvement in plant tolerance to water
deprivation
Aroca et al. 2012
AM symbiosis regulates the expression of key AQP genes and tightly
programmed root plant water status as well as the hydraulic
conductivity and tolerance under water deficiency
WATER ABSORBTION

61. WATER ABSORBTION
Chitarra et al.
2016
AM fungal-inoculated tomato plants, an enhancement in the water
transport capacity of AMF roots, correlated with overexpression of
NIP AQP-encoding gene.
Chaumont &
Tyerman SD,
2014
The absence of strong correlation between AQP genes expression
and hydraulic conductivity suggests that, with the enhancement in
hydraulic conductivity in plants inoculated by AMF, it might be
owed to other processes like enlarged expression and/or action in
plants AQP genes due to post-translational modifications of these
proteins
He et al. 2016
Some plant genes encoding AQPs were induced by AMF
colonization, as shown for RpPIP2;1 in Robinia pseudoacacia ,
which could be a way to upturn water flow in specific plant tissues,
vital for host existence under drought stress.

63. Oxidative Stress

64. OXIDATIVE STRESS
Production
of ROS
osmotic stress Damage to carbohydrate,
protein , lipid, DNA and
ultimately causes the
membrane damage and
cell death.
Enzymatic and non
enzymatic antioxidants

66. Osmotic Adjustment

67. OSMOTIC ADJUSTMENT
• Proline, an amino acid, plays a crucial role in
osmoregulation and acts as an efficient scavenger of reactive
oxygen species (ROS).
• Inoculation of either F. mosseae or Paraglomus occultum in
trifoliate orange plants substantially reduced leaf proline
content but improved the host plant growth under water
deficit.
• AMF strongly altered leaf proline metabolism through
regulating proline-metabolized enzymes, which is important
for osmotic adjustment of the host plants.
 PROLINE

68. • Sugars are osmoprotectants, which contribute up to 50% of
osmotic potential in plants.
• Under water stress, the higher accumulation of total soluble
sugars offers a defence mechanism in mycorrhizal plants such
as watermelon and flax.
• AMF-mediated increases in leaf sugar metabolism by
modulating sugar-metabolized enzymes notably contribute to
the osmotic adjustment of colonized plants.
• Under severe drought inoculation with Rhizophagus clarus
significantly reduced soluble sugars in leaves of strawberry
plants, but this parameter was remarkably enhanced in roots in
response to mild and severe water stress .
SUGARS

69. Plant defense System

70. Plant Defense System
• During the drought plant defense system it activated by production
of phyto-hormone. Those are-
1. Abscisic acid
2. Ethylene
3. Strigolactones
4. Auxin
5. Jasmonic acid
6. Salicylic acid
7. Cytokinins, gibberellins and Brassinosteroids

71. Abscisic Acid (ABA)
• A lower ABA concentration was found in roots and leaves of
mycorrhizal plants versus nonmycorrhizal plants under drought
stress .
• Downregulation of SlNCED gene, a critical ABA biosynthetic
gene, in Septoglomus constrictum -infected roots under water
stress concurred with the greater genes and higher water status of
tomato plants, indicating a higher stress tolerance in colonized
plants compared to uninoculated plants .Nonetheless, an
increase in ABA concentration in trifoliate orange plants colonized
by F. mosseae was also observed under drought stress .
• The reason for this remains poorly understood, which requires
further research.

72. Jasmonate (JA)
• Water uptake and transport, exerting influence on stomatal conductance, root
hydraulic conductance, and regulating the expression and abundance of
aquaporins .
• Plants defective in JA synthesis altered the AM impacts on the host plant,
interfering phytohormones and expression of AM-induced aquaporin genes.
• Mycorrhizal inoculation substantially increased methyl jasmonate (MeJA) in
trifoliate orange plants exposed to drought stress.
• Under water-stress conditions, significantly higher expression levels of JA-
biosynthetic gene SlLOXD in roots and leaves of colonized tomato plants were
detected, supporting plant response to drought stress by triggering a LOXD-
mediated pathway.

73. Strigolactones (SLS)
•Not only modulate the coordinated development of plants
exposed to nutrient shortages but are also host detection
signals for AM establishment in the host plant .
•Upregulation of the SL-biosynthesis gene SlCCD7 together
with a greater content of SLs was found in Rhizophagus
irregularis-inoculated tomato roots subjected to water-stress
conditions, correlated with the increase in AM colonization
rate.
•The stimulated production of SLs promoting symbiosis
establishment as a strategy of plants to cope with drought
stress has been proposed.

74. Auxin
• Regulator in root-hair initiation, growth, and developmental processes .
 In a recent study, an increased content of indole-3-acetic acid (IAA) which is
the dominant naturally occurring auxin was found in mycorrhizal tomato plants
exposed to drought.
• Under drought conditions, AM colonization PtYUC3 and PtYUC8 involved in
IAA biosynthesis, and downregulated auxin efflux carriers
(PtPIN1 and PtPIN3), while up-regulated auxin-species influx carriers
(PtABCB19 and PtLAX2) in roots, leading to significantly higher IAA
accumulation in mycorrhizal roots .
• Together with higher IAA, colonized trifoliate orange plants showed a
significant increase in MeJA, nitric oxide, and calmodulin in roots,
supporting greater root adaptation of morphology as a crucial strategy for
drought adaptation.

75. Gene Expression

76. Effect on The Expression of Gene
Porcel and Ruiz-
Lozano, 2004
Two Δ-pyrroline-5-carboxylate synthetase genes, gmp5cs from Glycine
max e lsp5cs from Lactuca sativa, and three genes encoding for
dehydrins, gmlea8 and gmlea10 (G. max) and lslea 1 (L. sativa), were
down-regulated in the roots of the respective plants under AM
inoculation
Aroca et al., 2006 In Phaseolus vulgaris roots colonized by Glomus intraradices, drought
treatment increased the expression of the aquaporin PvPIP1;1 gene,
drastically diminished the expression of the PvPIP1 ; 2 and PvPIP1 ;
3 genes, and did not change the expression of the PvPIP2;1 gene. Non-
AM control plants revealed higher gene expression of the analysed
transcripts during drought, except for PvPIP1;2

77. Effect on The Expression of Gene
Hanan Itzhaki
et al.
expression of tobacco genes following early stages of
Glomuse intraradix colonization were compared, thirty bands
in total RNA and cDNA from both AM and NM roots were
found in mycorrhyzal tobacco roots but not in NM roots,and
about 40 bands were found to be lighter or absent in the
mycorhiazal roots as compared with NM roots.
G. Berta et
al.2000
nuclei of AM colonized and control roots, and a strong
correlation between nuclear polyploidization and VA
colonization was found.
Taylor
J.,Harrier L.A.,
2003
gene expression patterns within leaf and root tissue of AM
and NM tomato plants were compared and differential
regulation was observed

78. Aquaporins,large major intrinsic protein family of transmembrane
proteins act as water channels are crucial in osmoregulation.
AMF could induce changes in the expression of various AQP genes
in the host in order to strengthen root hydraulic conductivity and host
tolerance under water-stress conditions in several plants.
AM-induced alterations in expression of plant AQPs could depend
on stress duration as the observation in maize plants .
Under short-term water deficit, the AM symbiosis upregulated ten
AQP genes with diverse aquaporin classes in roots inoculated
with Rhizophagus intraradices, stimulating more water uptake in the
host.
AMF- induced changes in expression of aquaporin
genes

79. AMF- induced changes in expression of aquaporin
genes
• Under sustained water-stress conditions, AM-mediated downregulation of
6 different AQP genes was found, restricting plant water loss
• Drought-sensitive cultivars may gain higher physiological benefit from
AM inoculation than drought-tolerant cultivars [Quiroga et. al.,2017 ].
• Downregulation of genes TIP1;1, TIP2;3, PIP1;1, PIP1;3, PIP1;4,
PIP1;6, PIP2;2, and PIP2;4 whereas only upregulation of TIP4;1 were
observed in drought-sensitive cultivar colonized by Rhizophagus
irregularis, supporting the decrease in water loss in host plants subjected
to drought stress .
• In parallel, it has been proposed that during drought stress a controlled
mechanism mediated by the presence of arbuscules at cortical cells in
roots fine-tuned the gene expression regulation in the host plant.

80. Future Perspectives
• Using the noninvasive micro-test technique (NMT) to monitor
dynamic changes in specific ions/molecules (including K+, Na+,
Ca2+, H+, Cl−, Mg2+, H2O2, IAA, and glucose) noninvasively after
AMF inoculation.
• Detecting ROS accumulation in roots and AM structure to further
confirm the functioning of AM on ROS accumulation, as well as the
functioning of ROS on AM development.
• Combining of AMF with other plant growth-promoting rhizobacteria
can be used in further works to clarify the synergy effect on drought
tolerance of the host plant.

81. Future Perspectives
• Analyzing the role of GRSP in soil structure and subsequent
improving soil/plant water relations.
• Utilizing RNA-seq technique to understand changes in
metabolic pathways and to screen differentiated expressed
genes in whole genes, which are confirmed by qRT-PCR for
the relative expression.
• Clarifying the perspectives in the study of aquaporins under
drought stress, as well as other stress conditions in both
drought tolerance and AM symbiosis.

82. Conclusion
• AM symbiosis often results in altered rates of water movement into, through and
out of host plants, with consequent effects on plant morphology and physiology.
The mechanisms of AM enhancing resistance of drought stress are still debated
now.
• Two aspects are necessary when AM symbiosis enhance resistance of high stress of
host plants, one is AM symbiosis activating defence system of host plant quickly;
and the other is some biochemical compounds that can resist high stress are
synthesized by AM symbiosis.
• Although we do not understand clearly how AM fungi activated defence system of
host plant, and whether there are other mechanisms concerned with the interaction
of AM fungi and its host plants, it is just the case that AM symbiosis enlarges
absorption areas of host plant, and improves nutritional status of host plant.
Therefore the conclusion that contribution of AM symbiosis to plant drought
tolerance is the result of accumulative physical, nutritional, physiological and
cellular effects is available.

83. Reference
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85. Composition of Advisory committee
Name Designatio
n
Department Role
Dr. Sunil Kr. Gunri Associate
Professor
Department of Agronomy Chairperson
Prof. Champak kr.
Kundu
Professor Department of Agronomy Member
Prof. Birendra Nath
Panja
Professor Department of Plant
Pathology
Member
Dr. Tapas Biswas Associate
Professor
Department of Soil Sci. &
Ag. Chemistry
Member