ROLE OF MICROBES IN SALT TOLERANCE OF PLANTS

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ROLE OF MICROBES IN SALT TOLERANCE OF PLANTS
BY PROF. DR. ASGHARI BANO
DEPARTMENT OF PLANT SCIENCES, QUAID-E-AZAM
UNIVERSITY ISLAMABAD
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• 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.

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SALINITY INDUCES SEVERAL PHYSIOLOGICAL CHANGES
Ionic imbalance
Water stress
Production of reactive oxygen species
Changes in the level of phytohormones
Unavailability of phosphate
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• 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

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• 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) Rice
A. brasilense Hartman et al (1991)  
A. brasilense cd Fischer et al (2000) Wheat
A. brasilense sp7 Tripathi et al (1998)  
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MICROBIAL SPECIES REFERENCES CROP STUDIED
A. brasilense Puente et al (1999) Sea water and mangrove seedlings
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
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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) Medicago truncatula
B. japanicum Miransari and Smith (2008) Soybean
Pseudomonas sp. Strain ADP Sharper et al (1998)  
P. trivialis Pratibha et al (2009) Cold deserts of trans Himalaya
P. kilonensis   Cold deserts of trans Himalaya
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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
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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
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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 PS
Salicylic acid (10-4 M) SAS
Azospirillum NaCl AS
Pseudomonas Salicylic acid NaCl PSAS
Azospirillum Salicylic acid NaCl ASAS
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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.

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SAMPLING PROCEDURE

• Young and fully expanded leaves were collected
  around 1000h-1200h 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).

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• 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.

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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) Soil moisture content (age) Soil moisture content (age)
Treatments Hy-sun Par-sun
C 14.00b 24.50b
S 32.47a 34.37a
PS 28.00a 19.90b
SAS 18.97b 19.67b
AS 19.30b 20.20b
PSAS 17.10b 18.63b
ASAS 16.80b 18.53b
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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 Hy-sun Par-sun Par-sun
RWC () OP(-MPa) RWC () OP(-MPa)
C 50.03ab 1.113a 50.47a 1.175a
S 46.07b 0.674b 40.60b 0.722c
PS 45.73b 1.023a 47.57ab 1.052ab
SAS 46.40b 1.086a 50.07a 1.023ab
AS 41.13b 0.988a 47.57ab 0.893bc
PSAS 57.57a 1.080a 55.53a 1.042ab
ASAS 41.97b 1.106a 48.37ab 1.007ab
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Table 5 EFFECT OF AZOSPIRILLUM, PSEUDOMONAS AND
SALICYLIC ACID ON CAROTENOID CONTENT OF TWO
SUNFLOWER CULTIVARS UNDER SALT STRESS
Treatments Hy-sun Par-sun
Treatments Carotenoid (mg/g) Carotenoid (mg/g)
Control 2.26 a 2.150 a
Salt treated 0.60 c 1.440 b
PseudomonasSalt 1.81 ab 1.743 ab
Salicylic acidSalt 2.17 a 1.960 a
AzospirillumSalt 1.15 bc 1.423 b
PseudomonasSalicylic acidSalt 2.15 a 1.700 ab
AzospirillumSalicylic acidSalt 1.60 ab 1.843 ab
LSD value 0.959 0.4567
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• 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 up-regulating antioxidant
  enzymes.

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• 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)

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• 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.

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