• Salinity is one of the most serious factor, limiting the
productivity of agricultural crops, with adverse effects on
germination, plant vigour and crop yield (R Munns & Tester,
• It is estimated that 6 per cent
of world´s total land and 20 per
cent of the world´s irrigated
areas are affected by salinity.
There is a deterioration of
about 1 per cent of world
agricultural lands because of
salinity each year. (Turan et al. 2012)
4. •Saline soils refers to a saturated soil paste
extract has an electrical conductivity of more than
4 ds/m (earlier mMhos/cm), ESP <15% and low
pH < 8.5
• Excess salt in the soil, reduces the water content
potential of the soil and making the soil solution
unavailable to the plants (Physiological Drought)
What is Salinity?
•Salinity is caused due to high accumulation of calcium,
magnesium as well as sodium and their anions such as
-2 , NO3
- , HCO3
- , CI- , CO3
•In a salt affected soils , there is an excess
accumulation of soluble salts in the root zone leading
to detrimental effect on plant growth and development.
Salinity tolerance is strongly influenced by other
factor i.e. Growth stage of the crop,
temperature, moisture stress etc.
•The relative growth of plants in the presence of
salinity is termed their salt tolerance.
Soil Salinity Class
Conductivity of the
Effect on Crop Plants
Non saline 0 - 2 Salinity effects negligible
2 - 4
Yields of sensitive crops may
4 - 8
Yields of many crops are
8 - 16
Only tolerant crops yield
Very strongly saline
Only a few very tolerant crops
Table 1 : Soil Salinity Classes and Crop Growth
Country Total land
Area irrigated Area of irrigated land
that is salt-affected
Mha % Mha %
China 97 45 46 6.7 15
India 169 42 25 7.0 17
Russia 233 21 9 3.7 18
United States 190 18 10 4.2 23
Pakistan 21 16 78 4.2 26
Iran 15 6 39 1.7 30
Thailand 20 4 20 0.4 10
Egypt 3 3 100 0.9 33
Australia 47 2 4 0.2 9
Argentina 36 2 5 0.6 34
South Africa 13 1 9 0.1 9
Subtotal 843 159 19 29.6 20
World 1,474 227 15 45.4 20
Table 2: Global Estimate of salinisation in the world’s irrigated lands
• Poor water management
• High evaporation
• Heavy irrigation
• Previous exposure to seawater
Causes of Soil Salinity
Adverse effects of salt stress
•Interferes with plant growth and development.
• Leads to physiological drought conditions and ion toxicity.
• Nutritional Disorder
• High salt deposition - Leads to formation of low water potential
zone in the soil.
• Higher concentrations of Na+ (above 100 mM)
Toxic to cell metabolism
Can inhibit the activity of many essential enzymes, cell
division and expansion and osmotic imbalance which leads to
Mechanism Of Salt Resistance
Primary stress Secondary stress
Osmotic stress tolerance
of salt in
of organic solutes
of K+ by Na+
Why is it necessary to develop salt
• The world population is increasing rapidly and may
reach 7 to 9.3 billion by the year 2050,whereas the
crop production is decreasing rapidly because of the
negative impact of salinity and other environmental
stresses (Varshney et al., 2011).
• Rapid shrinking agricultural land due to
industrialization and Urbanisation are major threat to
sustainable food production.
• So, it is almost necessary to raise salt tolerant plants
to effectively use salt affected lands for sustainable
Achievement Through Conventional
• To improve the crop yield and quality improving the
resistance of crops against abiotic stresses, especially
salinity stress through conventional method develop
salt tolerant variety.
•Some lines/cultivars of alfalfa (Medicago sativa L.)
such as AZ-Germ Salt II (Dobrenz et al., 1989), AZ-
90NDC-ST (Johnson et al., 1991), AZ- 97MEC and
AZ-97MEC-ST (Al-Doss and Smith,1998), ZS-9491 and
ZS-9592 (Dobrenz, 1999)
•Two salt-tolerant lines/cultivars of bread wheat (Triticum
aestivum L.) such as S24 (Ashraf and O'Leary, 1996) and
KRL1-4 (Hollington, 2000) were evaluated on natural salt-
Non Conventional Approach
Molecular Approach (MAS)
TILLING (Targeting Induced Local Lesions IN
•Transgenic plants for ion transporters
•Transgenic plants for compatible organic solutes
•Transgenic plants for enhanced antioxidant production
•In Tomato fruit crop a vacuolar Na+/H+ antiport
(AtNHX1) from A. thaliana lead to salt
accumulating in the leaves of the plants, but not
in the fruit and allowed them to grow more in
salt solutions than wildtype plant
•In response to high salinity stress, various genes get
upregulated, the products of which are involved either
directly or indirectly in plant protection against salt stress.
• Some of the genes encoding osmolytes, ion channels,
receptors, components of calcium signaling and some
other regulatory signaling factors or enzymes are able to
confer salt tolerant phenotypes when transferred to
Allele mining : finding of superior allele from the natural
Introgression of novel or superior
Allele from wild relatives into Cultivated one
Problems In Breeding For Salinity
1. There is no simple to score, reliable and
dependable selection criterion for salinity
2. Creation of reliable, dependable and controlled
salinity environment for selection work is tedious,
costly and beyond reach of many breeders.
3. The genetic control of salinity resistance is
generally complex and polygenic, which makes
transfers from germplasm lines and especially,
related species a very difficult task.
4. The basis of salinity resistance is poorly
understood, this makes genetic analysis and
breeding efforts considerably difficult.
Fig. 1 : Genes associated with the salt tolerance mechanism
1. Osmolytes synthesis
2. Ion Pumps, Calcium
4. Reactive Oxygen Species (ROS)
5. LEA (Late Embryogenesis Abundant ) Protein
6. Signalling Molecules
7. Abscisic Acid and Transcription Factors
Several mechanisms of Salt tolerance
2. ION PUMPS, CALCIUM, AND SOS PATHWAYS
Fig. 2 : Regulation of ion(e.g.,Na+, K+and Ca2+) homeostasis by SOS and related
pathways in relation to salt stress tolerance.
HKT-histidine kinase transporter
NHX-vacuolar Na+/H+ exchanger
31. 3. HELICASES
• Helicases catalyze the unwinding of energetically stable duplex DNA or duplex
RNA secondary structures.
• Most helicases are members of the protein superfamily that play essential roles in
basic cellular processes regulating plant growth and development.
• RNA helicases are the best candidates for RNA chaperones because these
proteins can actively disrupt misfolded RNA structures in ATP dependent manner.
• There could be two possible sites of action for the helicases:
• At the level of transcription or translation to enhance or stabilize protein
• In an association with DNA multisubunit protein complexes to alter gene
32. 4. Reactive Oxygen Species
• Reactive Oxygen Species produced in response to oxidative stress can
cause permanent damage to the cellular apparatus.
• Reactive oxygen intermediates (ROI) typically result from the excitation
of O2 to form singlet oxygen (1O) or the transfer of one, two, or three
electrons to O2 to form superoxide radical (O2
- ), hydrogen peroxide (H2O2),
or a hydroxyl radical (OH-), respectively.
• The ROIs react spontaneously with organic molecules and cause
membrane lipid peroxidation, protein oxidation, enzyme inhibition, and
DNA and RNA damage.
• The major ROI-scavenging enzymes of plants include superoxide
dismutase (SOD), ascorbate peroxidase, catalase, and Glutathione
5. Signalling molecules
• Exposure of any stress to plants causing
change in normal plant development is
sensed by sensor which leads to a
signaling cascade resulting in a stress
response by plant.
• Mitogen-activated protein kinases -
serine/ threonine protein kinases that play a
central role in the transduction of various
extracellular and intracellular signals,
including stress signals.
Kaur and Gupta, (2005)
Fig. 9 : MAPK cascade
External ( Environmental
Internal (Growth Factor)
Substrates : Transcritional Factors
6. LEA-Type Proteins
• Late embryogenesis Abundant proteins are a group of
hydrophilic proteins produced late during embryo development,
and constitute about 4 per cent of the total cellular proteins.
Acting as hydrating buffers
Helping in renaturation of proteins
Act as chemical chaperones
• These proteins can be induced by ABA and various water-
related stresses including salinity.
35. ZEP- zeaxanthin epoxidase;
NCED- 9-cis-epoxycarotenoid dioxygenase;
MCSU- molybdenum cofactor sulfurase.
7. Abscisic Acid and Transcription Factors
Fig. 10 : ABA biosynthesis
pathway and its
regulation by osmotic
Screening Techniques For Tolerance to Moderate Salinity
(50 – 150 mM NaCl)
Measurements of growth:
Biomass and Yield
Measurements of injury:
Leakage from leaf discs
Screening For High salinity
(200–300 mM NaCl)
Fig. : The grain size of
wildtype Hesheng 3
and transgenic line
grown in normal and
saline soil in the
Fig. : Effects of salt on
the growth of AtNHX1
transgenic wheat lines
(T2) in absence and
presence of 150mM
NaCl for 30 days.
Less growth retardation and
longer root length
Fig. : Whole plants after 30-days of salt treatment.
40. Name of gene Source species Gene product Function Harbourg
betA E. coli Choline
Betaine synthesis Tobacco
Betaine synthesis Tobacco
CodA A. globiformis Choline oxidase Betaine synthesis Arabidopsis
COX A. pascens Choline oxidase Betaine synthesis Arabidopsis
TUR1 A. polyrriza Inositol synthase InsP3 synthesis Arabidopsis
IMT M.crystalinum Myo-inositol O-
MtlD E.coli Mannitol 1-
Mannitol synthesis Arabidopsis
P5CS V. aconitifolia Pyrroline-5-
Proline synthesis Tobacco, Rice
HVA1 H. vulgare LEA protein Protein protection Rice
DREB1A A. thaliana Transcription factor Improve gene
CaN S. cereviseae Calcineurin Improve Ca2+
Table 3 : Salt resistant genes and their functions
•Salt tolerance is a complex trait that involves coordination of
many signalling pathways involving action of various genes.
• Understanding molecular mechanisms are helpful in over
expression of existing gene and introduction of various salt
tolerant genes from bacteria and halophytes into salt sensitive
• Majority of salt tolerant plants produced by transformation
are tested for tolerance under laboratory control condition.
• Molecular approaches for modification of ion pump regulator
and synthesis of osmo-protectant, LEA protein, ROS and
helicases are efficient to produce salt tolerant plants.
•Role of endogenous RNA in regulating the salinity tolerance has to
• Use of promoters that direct the expression at proper time and
location will maximize salt tolerance
• Use of more advanced and less time consuming technologies like
multi SNP analysis are required.
•Identifying and validating novel genes in crops that will significantly
improve its performance under salinity stress.
•salt stress tolerance of plants is a complex trait and involves
multiple physiological, biochemical mechanisms and a wide array of