ROLE OF MICROBES IN SALT TOLERANCE OF
PLANTS
BY
PROF. DR. ASGHARI BANO
DEPARTMENT OF PLANT SCIENCES, QUAID-EAZAM UNIVERSITY ISLAMABAD
SALINITY
“A major stress limiting agriculture productivity’’.
 APPROACHES TO COMBAT SALINITY:
1)Chemical amendment
2)Development of salt tolerant plants through
breeding/genetic engineering.
3)Role of Agrochemical
The alternative viable approach; use of salt tolerant microbes
to induce tolerance in plants,economical,sustainable &
environment friendly.
SALINITY INDUCES SEVERAL
PHYSIOLOGICAL CHANGES
Ionic imbalance
Water stress
Unavailability of phosphate
Production of reactive Changes in the
oxygen species
level of
phytohormones
 SALT TOLERANCE LIMIT:
• Threshold level of salt tolerance in plants varies from
40-200mM NaCl.
• Tolerance level of PGPR varies from 100-650mM
NaCl.
 ROLE OF PGPR:
a) Better development of root system
b)Production of growth promoting hormones in addition
to stress hormone ABA.
c)Solubilization of insoluble phosphate
Table. 1: LIST OF SOME IMPORTANT MICROBIAL SPECIES
TOLERANT TO SALT STRESS
MICROBIAL SPECIES
REFERENCES
CROP STUDIED
Azospirillum brasilense strain
Az 39
Cassan et al (2008)
Rice (cv. L-Paso 144)
A. brasilense sp 245
Creus et al (1997)
Triticum aestivum
(Wheat)
A. brasilense cd
Rivarola et al (1998)
A. brasilense
Saleena et al (2002)
A. brasilense
Hartman et al (1991)
A. brasilense cd
Fischer et al (2000)
A. brasilense sp7
Tripathi et al (1998)
Rice
Wheat
MICROBIAL SPECIES
REFERENCES
CROP STUDIED
A. brasilense
Puente et al (1999)
Sea water and
seedlings
mangrove
A. amazonense
Tripathi et al (1998)
A. lipoferum
Hartman etal (1991)
A. lipoferum
Saleena et al (2002)
Rice
A. lipoferum JA 4 ngfp15
Bacilio et al (2004)
Wheat
A. lipoferum
Puente et al (1999)
Saline paddy soil,
sea weeds
A. halopraferans
Puente et al (1999)
Sea water and mangrove
seedlings
A. halopraferans
Reinhold
Kallar grass
MICROBIAL SPECIES
REFERENCES
CROP STUDIED
A. halopraferans
Hartman et al (1991)
Serratia proteamuculans
Hans and lee (2005)
Soybean
Bacillus Subtilis GBO3
Zhang et al (2008)
Rice
Klebsiella oxytoca
Yhe et al (2007)
Sinorhizobium meliloti 2011
Aydi (2008)
B. japanicum
Miransari and Smith Soybean
(2008)
Pseudomonas sp. Strain ADP
Sharper et al (1998)
P. trivialis
Pratibha et al (2009)
P. kilonensis
Medicago truncatula
Cold deserts
Himalaya
of
trans
Cold deserts
Himalaya
of
trans
MICROBIAL SPECIES
REFERENCES
CROP STUDIED
P. corrugata
Cold deserts of trans
Himalaya
P. jessenic
Cold deserts of trans
Himalaya
P. movaviensis
Cold deserts of trans
Himalaya
P. flourecens MSP-393
Paul and Nair (2008)
Coastal agricultural soil
P. mendocina
Naz (2008)
P. stutzeri
Naz (2008)
Aspergillus flavus
Hassan (2002)
Faba bean
Aspergillus niger
Hassan (2002)
Sesame
MICROBIAL SPECIES
REFERENCES
CROP STUDIED
Fusarium oxysperum
Hassan (2002)
Soybean
Rhizopus stolonifer
Hassan (2002)
Soybean
Glomus intraradices
Kohler et al (2004)
Lactuca sativa (L.)
Achramobacter piechandii
Mayak et al (2004)
Tomato seedlings
R.leguminosarum and
Bradyrhizobium sp.
Elsiddig and Elsheikh
(1998)
Rhizobium leguminosarum bv.
Vicia 3841
El-Hamdaoui et al
(2003)
Pea
Rhizobium leguminosarum bv.
Vicia strain GRA19
Cordovilla et al (1996)
Vicia faba
Frankia sp.
Reddell et al (1985)
Casuarina obsesa
Scytanema hofmanni
Rodriguez et al (2006)
rice
Table 2: COMPARATIVE EVALUATION HAVE BEEN MADE FOR THE
ROLE OF PGPR AND SALICYLIC ACID IN IMPARTING SALT
TOLERANCE TO SUNFLOWER PLANTS ( NAZ AND BANO 2009)
Treatments
Symbols
Control
C
NaCl (20dsm-1)
S
Pseudomonas + NaCl
P+S
Salicylic acid (10-4 M)
SA+S
Azospirillum + NaCl
A+S
Pseudomonas + Salicylic acid + NaCl
P+SA+S
Azospirillum + Salicylic acid + NaCl
A+SA+S
MATERIAL AND METHODS
• The seeds were soaked overnight in cultures of
Azospirillum and Pseudomonas prior to sowing
NaCl (20dSm-1)were applied to soil 4 weeks after
inoculation
• Aqueous solution of 20dSm-1 NaCl was applied the
rhizosphere soil of potted plants till saturation and
watering was made to all the treatments as and when
required.
• Salicylic acid (10-4M) foliary applied to plants 4h
after the salt treatment.
SAMPLING PROCEDURE
• Young and fully expanded leaves were collected
around 10:00h-12:00h to analyze the relative water
content, osmotic potential, carotenoid content, proline,
antioxidants and hormones 7d after the induction of
salt treatment.
• Relative water content of second leaf from the top of
the plants was determined following the method given
by Gupta (1995).
• The osmotic potential of the cell sap was measured
leaves with a freezing point osmometer according the
method of Capell and Doerffling(1993).
• Carotenoid content was estimated according to the
method of Lichtenthaler and Wellburn (1983).
• Proline content of young leaves was estimated by using
the following method of Bates et al. (1973).
SAMPLING PROCEDURE
• SOD of fresh plant tissues was determined following the
method of Beauchamp and Frodovich (1971).
• POD activity of fresh plant tissues was measured by the
method of Vetter et al. (1958) as modified by Gorin and
Heidema (1976).
• The extraction and purification of ABA was made
following the method of Kettner and Droffling, (1995).
• The extraction and purification of ABA was made
following the method of Kettner and Doerffling, (1995).
• Salicylic acid was extracted and purified according to
the method of Enyedi et al., 1992 and Seskar et al.,
(1998) with some modifications.
Table: 3 Effect of Azospirillum, Pseudomonas and
Salicylic acid on soil moisture content of two
cultivars (cvv. Hy-sun & par-sun) under salt stress.
Soil moisture content (%age)
Treatments
Hy-sun
Par-sun
C
14.00b
24.50b
S
32.47a
34.37a
P+S
28.00a
19.90b
SA+S
18.97b
19.67b
A+S
19.30b
20.20b
P+SA+S
17.10b
18.63b
A+SA+S
16.80b
18.53b
Table 4: Effect of Azospirillium, Pseudomonas and Salicylic Acid on
Relative Water Content (%age) and Osmotic Potential (-MPa) of two
Sunflower cultivators Hy-sun & Par-sun) under salt stress.
Treatments
Hy-sun
RWC (%)
Par-sun
OP(-MPa)
RWC (%)
OP(-MPa)
C
50.03ab
1.113a
50.47a
1.175a
S
46.07b
0.674b
40.60b
0.722c
P+S
45.73b
1.023a
47.57ab
1.052ab
SA+S
46.40b
1.086a
50.07a
1.023ab
A+S
41.13b
0.988a
47.57ab
0.893bc
P+SA+S
57.57a
1.080a
55.53a
1.042ab
A+SA+S
41.97b
1.106a
48.37ab
1.007ab
Table 5: EFFECT OF AZOSPIRILLUM, PSEUDOMONAS AND SALICYLIC
ACID ON CAROTENOID CONTENT OF TWO SUNFLOWER CULTIVARS
UNDER SALT STRESS
Treatments
Hy-sun
Par-sun
Carotenoid (mg/g)
Carotenoid (mg/g)
Control
2.26 a
2.150 a
Salt treated
0.60 c
1.440 b
Pseudomonas+Salt
1.81 ab
1.743 ab
Salicylic acid+Salt
2.17 a
1.960 a
Azospirillum+Salt
1.15 bc
1.423 b
Pseudomonas+Salicylic
acid+Salt
2.15 a
1.700 ab
Azospirillum+Salicylic
acid+Salt
1.60 ab
1.843 ab
LSD value
0.959
0.4567
1200
1000
Proline (ug/g)
a
a
a
a
a
a
800
600
a
b
c
c
bc
ab
Hy-sun
c
c
400
200
0
C
S
P+S
SA+S
A+S
TREATMENTS
P+SA+S A+SA+S
Par-sun
SOD (units / g fw)
4
3.5
3
2.5
2
1.5
1
0.5
0
a
a
ab
a
b
ab
a
a
b
a
a
a
Hy-sun
Par-sun
b
c
C
S
P+S
SA+S
A+S
P+SA+S A+SA+S
TREATMENTS
Fig. 2 Effect of Azospirillum, Pseudomonas and Salicylic acid on
SOD (units/g fw) of two sunflower cultivars under salt stress
POD (min -1 g-1 fw)
1.2
a
1
a a
0.8
0.6
b
a
ab
abc
bc
b
b
a
bc
ab
Hy-sun
c
Par-sun
0.4
0.2
0
C
S
P+S
SA+S
A+S
P+SA+S A+SA+S
TREATMENTS
Fig. 3 Effect of Azospirillum, Pseudomonas and SA on POD (min1g-1 fw) activity of two sunflower cultivars under salt stress
400
a
ABA (ug/g) in leaves
350
300
250
200
Hy-sun
150
Par-sun
100
50
b c
b b
b ab
b a
S
P+S
SA+S
b
ab
b ab
a
0
C
A+S
P+SA+S A+SA+S
TREATMENTS
Fig. 4 Effect of Azospirillum, Pseudomonasand Salicylic acid on ABA
accumulation in leaves of sunflower cultivars under salt stress
Salicylic acid contents of fresh leaves (ug/g)
40
a
35
Hy-sun
30
a
Par-sun
25
b
20
bc
15
10
b
b
cd
c
de
b
de c
e d
5
0
C
S
P+S
SA+S
A+S
P+SA+S
A+SA+S
TREATMENTS
Fig: 5 Effect of Azospirillum, Pseudomonas and Salicylic acid on Salicylic
acid contents of leaves under salt stress
DISCUSSION
• Proline content and superoxide dismutase
activity may be used as physiological
markers of salt tolerance as they showed
more increase in salt tolerant Hy-Sun 33.
• Plant Growth Promoting Rhizobacteria
(e.g. Azospirillum and Pseudomonas)
receiving the foliar spray of SA and SA
application alone may have a role in upregulating antioxidant enzymes.
CONCLUSION
The possible difference between microbes (PGPR) induced
salt tolerance and hormone induced salt tolerance can be
summarized as follows:
• Microbes are sustainable source of ABA production along
with other growth promoting hormones IAA, GA and t-zr
whereas, ABA applied exogenously to combat salt stress
decreases the endogenous level of IAA, GA and t-zr. ABA
is a growth inhibitory compound and under normal
condition its level should remain low to keep pace with
growth and development.
• Particularly in sensitive varieties, it has been reported that
on return to normal condition the decline in stress induced
ABA level was delayed and magnitude of decrease was
also less. (Iqbal and Bano 2009)
•
Microbes can also produce other bioactive
metabolites e.g. polyamines (Putrescine,
cadavarine etc) which further improve the plant
resistance to disease and salt.
•
Microbes assist in solubilization of P and make
them available to plant which is an additional
effect not the case in ABA-induced salt
tolerance .
•
Microbes are economical and environmental
friendly whereas, ABA is rather expensive and
may have adverse effects on soil microbiota.