The document discusses mechanisms of salinity tolerance in plants. It describes how plants can tolerate high salt concentrations through avoidance, tissue tolerance, and salt dilution. Avoidance mechanisms keep salt ions away from sensitive plant tissues through exclusion, excretion, or compartmentalization of ions. Tissue tolerance allows plants to tolerate accumulated ions through compartmentalization at the cellular and intracellular levels. Salt dilution increases plant storage volume to dilute ion concentrations. The document provides examples of plant species that exhibit different tolerance mechanisms and strategies to mitigate the effects of salinity on crops.

1. Submitted by :
P.TEJASREE
BAM-20-27
M.Sc 1st Year
Dept of GPBR
Salinity stress Resistance Mechanisms in
Plants – Avoidance (exclusion , extrusion
, excretion , dilution)

2. SALINITY
 Soil salinity is an issue of global importance causing many socio-economic problems
 It also results in losses of (806.4 billion rupees) per year to agriculture.
Salinity: It is caused due to high accumulation of Calcium, Magnesium as well as sodium
and then anionssuch as SO -2, NO -, CO -2 and HCO -, Cl-, etc.
• Excess salt in the soil, reduces the water potential of the soil and making the soil solution
unavailable to the plants (physiological drought).

3. SALINE AND SODIC SOILS
Saline soil : is soil containing sufficient soluble salt to adversely affect the growth of
most crop plants with a lower limit of electrical conductivity of the saturated extract
(ECe) being 4 deci Siemens / meter (dS/m), which is equivalent to a value of 4
mmhos/cm.
• Sodicity is a term given to the amount of sodium held in a soil. Sodium is a cation (positive
ion) that is held loosely on clay particles in soil. It is one of many types of cations that are
bound to clay particles. Other types bound to clay particles include calcium, magnesium,
potassium and hydrogen.

4. HEALTH AND QUALITY OF SALINE
AFFECTED SOILS
• High concentration of salts reduces the productivity of nearly 6.73 Mha in India.
• Continuous use poor quality of water for irrigation increase the problem of salinity
and sodicity in India.
• The projections indicate that the country will have 11.7 m ha area affected by salinity and
sodicity by 2025.

5. From reclamation and management point of view, the salt affected soils in India are
broadly placed into twocategories;
1) alkali soils and
2) saline soils.
The alkali soils having high soil pH (upto 10.8), high exchangeable sodium percent
(ESP) up to 90, low organic carbon, poor infiltration and poor fertility status.
On the other hand, the saline soils have higher electrical conductivity (> 4 dS/m) ,
low ESP «15%)and low pH «8.5).

6. SALINITY STRESS EFFECTS ON
CROP GROWTH AND
DEVELOPMENT

7. TRANSPORT AND REGULATION OF SALT IN SOIL PLANT
SYSTEM

8. EFFECT OF SALT STRESS ON CROP GROWTH AND
DEVELOPMENT

11. Physiological Effects of
Salinity

12. GROWTH
• Decreased rate of leaf growth after an increase in soil salinity is primarily due to the
osmotic effect of the salt around the roots.
• Increase in soil salinity causes leaf cells to loose water.
• Reductions in cell elongation and also cell division lead to slower leaf appearance and
smaller final size

13. GERMINATION
• Seed germination in saline condition is affected by threeways:
• Increased osmotic pressure of the soil solution which restricts the absorption and
entry of water into the seeds.
• Certain salt constituents are toxic to the embryo
• Salt stress hampers the metabolism of stored materials.

14. VEGETATIVE GROWTH
• During vegetative stage, salt induced water stress causes closure of stomata leads to
reduction in CO2 assimilation and transpiration.
• Reduced turgor potential affects the leaf expansion.
• Because of reduction in leaf area, light interception is reduced, photosynthetic rate is
affected which coupled with spurt in respiration, resulting into reduced biomass
accumulation.

15. PHOTOSYNTHESIS
• Accumulation of high concentration of Na+ and Cl- in chloroplast, photosynthesis is
inhibited.
• Since photosynthetic electron transport appears relatively insensitive to salts, either
carbon metabolism or photophosphorylation may be affected.
• Photosynthetic enzyme or the enzymes responsible for carbon assimilation are very
sensitive to the presence of NaCl.

16. NITROGEN METABOLISM
• The key enzyme, nitrate reductase is very sensitive toNaCl .
• One of the amino acids, glycinebetaine shows increased trend with increase in salinity in
perennial halophytes andAtriplex sps.
• Proline is an αamino acid, accumulates in large amounts as compared to all other
amino acids in saltstressed plants.

17. REPRODUCTIVE GROWTH & YIELD
• Under salt stress condition, the onset of flowering is delayed due to the limitations of
source size.
• The quantum of reproductive structure such as number of flowers / panicle is very much
reduced.
• This disturbance in the normal metabolism affects the mobility of metabolites.
• Due to imbalance of nutrients under salt stress, hormone synthesis is hampered leads to
reduction in quantity as well as quality of crop produce.

18. OXIDATIVE STRESS
• Due to increase in salinity stress, photosynthetic rate decreases which increases
the formation of reactive oxygen species (ROS), and increases the activity of
enzymes that detoxify these species.
• Plants undergo adjustments in leaf morphology, chloroplast pigment composition, and
in the activity of biochemical processes that prevent oxidative damage to
photosystems.
• This maintains H2O2 at levels required for cell signalling.

19. GENES THAT REGULATE SALT STRESS

20. EFFECT OF SALINITY STRESS ON MORPHO-PHYSIOLOGICAL, BIOCHEMICAL
AND YIELD CHARACTERS OF CLUSTER BEAN [CyamopsisTetragonoloba (L.)
Taub.]
Deepika et al. 2014 Indian Journal of Plant Physiology (October–December ) 19(4):393–398

23. Based on the responses to high concentration of salts, plants can be divided into two
broad groups.
Halophytes
Glycophytes
Halophyte ( salt tolerant crops)
They are native to saline soils.
Glycophytes (Literally "sweet plants") Non halophytes
They are sensitive plants and unable to grow under saline conditions. Most of the cultivated crop
species belong to glycophytes.
CROPADAPTATIONS TO SALT STRESS

24. →PHYSIOLOGICAL ASPECTS OF
SALINITY TOLERANCE
TOLERANCE TO OSMOTIC STRESS
AVOIDANCE
SALT DILUTION

25. MECHANISMS OF SALINITY
TOLERANCE
1. Tissue tolerance to osmotic stress :The osmotic stress immediately reduces cell expansion in root
tips and young leaves, and causes stomatal closure.
• A reduced response to the osmotic stress would result in greater leaf growth and stomatal
conductance, but the resulting increased leaf area would benefit only plants that have sufficient
soil water.
• Greater leaf area expansion would be productive when a supply of water is ensured such as in
irrigated food production systems, but could be undesirable in water- limited systems, and cause the
soil water to be used up before the grain is fully matured.

27. 2. Avoidance : Avoidance is the process of keeping the salt ions away from the parts of the plant where
they are harmful.
•Salt exclusion : The ability to exclude salts occurs through filtration at the surface of the root. Root
membranes prevent salt from entering while allowing the water to pass through. The red mangrove is an
example of a salt-excluding species.
•Salt excretion/extrusion : Salt excreters remove salt through glands or bladders or cuticle located on each
leaf.
•Salt bladders - e.g.) Atriplex , Mesembryanthemum crystallinum L.
•Salt glands - active process, selective for sodium and chloride (e.g.) Black and white mangroves
•Secretion through cuticle – e.g.) Tamarix
•Salt glands- dump sites for the excess salt absorbed in water fromthe soil; help plants adapt to life in saline
environments.

30. Salt Dilution : By dilution of ions in the tissue of the plant by maintaining succulence. Plants achieve
this by increasing their storage volume by developing thick, fleshy, succulent structures Succulence is
mainly a result of vacuoles of mesophyll cells filling with water and increasing in size. This mechanism
is limited by the dilution capacity of plant tissues.
Compartmentation of ions : Organ level - high salts only in roots compared to shoots especially leaves
.At cellular level- high salts in vacuoles than cytoplasm thus protecting enzymes

31. 3. Tissue tolerance : tolerance of tissue toaccumulated Na+, or in some species, to Cl-.
• Tolerance requires compartmentalization of Na+ and Cl- at the cellular and intracellular
level to avoid toxic concentrations with in the cytoplasm, especially in mesophyll cells in
the leaf.
• Toxicity occurs with time, Na+ increases to high concentrations in the older leaves.

33. MITIGATION STRATAGIES
• Foliar spray of 0.5 ppm brassinolide for increasing photosynthetic activity
• Foliar spray of 2% DAP + 1% KCl (MOP) during critical stages
• Spray of 40 ppm of NAA for arresting pre-mature fall of flowers / buds / fruits
• Extra dose of nitrogen (25%) in excess of the recommended
• Split application of N and K fertilizers
• Seed treatment + soil application + foliar spray of Pink Pigmented Facultative Methnaotrops
(PPFM) @ 106 as a source of cytokinins

34. THANK YOU
Submitted to :-
Dr K.Jayalalitha
Associate Professor
Dept of Crop physiology