Abiotic stress factors or stressors are naturally occurring, often intangible factors The four major abiotic stresses: drought , salinity, temperature and heavy metals, cause drastic yield reduction in most crops. Few of the types of abiotic stresses are: 1)Water-logging & drought 2)Excessive soil salinity 3)High or low temperatures 4)Ozone 5)Low oxygen 6)Phytotoxic compounds 8)Inadequate mineral in the soil 9)Too much or too little light This presentation focuses on the adaptations in plants against abiotic stress and the ways that how they tolerate it with different mechanisms. - Haider Ali Malik

1. Adaptation in plants against
abiotic stress
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By Haider Ali Malik

2. OUTLINE
Introduction
Drought tolerance
Salt tolerance
Cold tolerance
Oxidative stress tolerance
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3. What’s in name?
Stress: Factors of environment interfering the complete
expression of genotypic potential.
Abiotic stress: The negative impact of non-living factors
on the living organisms in a specific environment.
Abiotic stress factors or stressors are naturally occurring,
often intangible factors
The four major abiotic stresses: drought , salinity,
temperature and heavy metals, cause drastic yield
reduction in most crops.
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4. Environmental conditions that can cause stress
Water-logging & drought
Excessive soil salinity
High or low temperatures
Ozone
Low oxygen
Phytotoxic compounds
Inadequate mineral in the soil
Too much or too little light
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5. Characteristics of abiotic stresses
Effects generated by one abiotic stress may overlap with
some effects of another stress.
Differential response of plant sp. to a given stress.
One stress may increase or decrease the level of another
stress.
Some stresses are impossible to manage.
Unpredictable occurrence.
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6. PLANT RESPONSE TO STRESS
Stresses trigger a wide range of plant
responses:
Changes in growth rates and crop yields
Cellular metabolism
Altered gene expression
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7. PLANT RESPONSE TO STRESS
Stress
Ozone
Extreme temperature
Flooding
Drought
Salt
Response
Physiological &
developmental event
Altered cellular
metabolism
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8. Resistance or sensitivity of plants to stress
depends on
Stress characters
• Severity
• Duration
• No of exposure
• Continuation of
stress
Plant Character
• Organs or tissues
in question
• Stage of
Development
• Genotype
Response and result
• Resistence Survival
and growth
• Susceptibility
Death
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9. Stress resistance mechanisms
Avoidance
- prevents exposure to stress
Tolerance
- permit the plant to withstand stress
Acclimation
- alter their physiology in response to stress
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10. Stress resistance mechanisms10
Abiotic Stress
Acclimation
Resistence
Stress avoidance
Stress Tolerance

11. I. DROUGHT STRESS
Drought:
Moisture scarcity which restricts the full expression of
genetic yield potential of a plant.
Mechanisms of drought resistance:
a) Drought escape: mature early
b) Drought avoidance: Maintain water balance
c) Drought tolerance: higher yield even under low water
potential
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12. Effects of drought at cellular level
Pressure differential across the membrane-cell wall complex;
in turn affects cell expansion.
Rate of translation.
Amounts of specific mRNA .
Structures of macromolecules like proteins and nucleic acids.
Structures of membrane and organelles.
A combination of the above.
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13. Morphological features providing drought
resistance
 Earliness
 Reduced tillering
 Leaf rolling, folding, shedding, leaf reflectance
 Reduced leaf area; narrow leaf, change in leaf angle
 Hairiness
 Color of leaves
 Wax coating
 Root systems
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14. Physiological response to drought
Reduced transpiration and reduced respiration
losses
Photosynthetic efficiency is reduced due to
chloroplast damage
Stomatal behavior
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15. Biochemical response to drought
Accumulation of compatible solutes
Increase in ABA and Ethylene
Protein synthesis
Nitrate reductase activity
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16. Sources of drought resistance
Transgenes : Rab (Responsive to abscisic acid) in
rice
Wild relatives: e.g. Wheat: A.variabilis,
A,speltoides, A.squarrosa Sugar cane: S.
spontaneum
Land races
Cultivated varieties
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17. Breeding methods and approaches
Approaches:
Varieties adapted to a specific environment
Adaptation to variable environment
Combining drought resistance traits with high
yield potential
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18. Breeding methods:
Genetic engineering
Mutation
Hybridization
Selection
Introduction
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19. Osmotic adjustment
In response to dehydration or osmotic stress a series
of compatible solutes/ osmolytes are accumulated for
osmotic adjustment, water retention and free radical
scavenging.
The cell actively accumulates solutes and as a result
the solute potential drops, promoting the flow of
water into the cell.
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20. Few osmolytes:
D-Pinitol
Osmotin
Mannitol
Glycine betaine
Proline
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21. Limitations
Generally resistant varieties have low yield; Do not have much
adaptability.
Drought resistant genes may have linkage with undesirable
genes.
Transfer of resistant genes from wild types may pose a
problem
Drought resistant traits may reduce yield.
Creation of controlled moisture stress environment is a
problem, selection require considerable resources
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22. Achievements
Potato: Rila, Viking
Maize: Early triumph, silver king
Sugarcane: Co 1148, Co 11158, Co 997
Ground nut: Jyothi, DH3-10
Durum wheat: Gulab, Motia, Jay, Vijay
Barley: Karan 280
Rice: Akashi, Bala, IRS
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23. II. SALT TOLERANCE
Salt tolerance: Ability of plants to prevent ,reduce or
overcome injurious effects of soluble salts present in their
root zone
Salinity can be overcome by
1)Soil reclamation: costly ,time consuming & short lived
2) Resistant varieties: less costly, more effective, long lasting
but require longer period to develop.
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24. Characteristics of plants to salt :
Land races more tolerant than high yielding
varieties
Salt tolerance capacity differs from species to
species
Different plants show differential response to
salinity
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25. Classification of plants based on salt
tolerance
1. Highly tolerant crops:
Sugar beet, barley, cotton, date palm, asparagus.
2. Moderately tolerant:
Barley, rye, sorghum, wheat, safflower, Soya been
3. Moderately sensitive:
Rice, corn, foxtail millet, cow pea, peanut, sugar cane,
tomato, potato, radish, cabbage
4. Extremely sensitive:
Citrus, strawberry, melon, peas, carrot, okra, onion.
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26. Symptoms of plant to salt stress
Retardation of growth
Necrosis
Leaf abscission
Loss of turgor
Ultimate death of plant
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27. Mechanism of salt tolerance
1. Salt tolerance:
By accumulating salt, generally in their
cells or glands & roots.
Halophytes show tolerance by ion
accumulation mechanism
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28. 2. Salt avoidance:
By maintaining their cell salt concentration
unchanged either by water absorption (e.g. Rice,
chenopodiaceae) or by salt exclusion (e.g. tomato,
Soya bean, citrus, wheat grass)
Glycophytes (nonhalophytes) owe their resistance
primarily to avoidance e.g. barley
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29. Breeding strategies
Selection should be done in stresses target
environments
Breeding for yield potential should have greater
emphasis than breeding for salt resistance.
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30. Screening techniques
1. Sand culture by using nutrient solution in sand &
irrigation with saline water.
2. Solution culture by using solution culture tanks
3. Micro plot techniques by using small micro plots.
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31. Achievements
Rice : Mohan, pokkali, SR23b, SR26b, CSR-2,
CSR-3, CSR-6.
Onion: Hissar-2, pb selection, Karchia, Karna-92.
Okra: Pusa Sawani
Barley: Ratna, RS-16, Karan-18, 19, 92
Sugar cane: Co7717, Co1148, Bo91
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32. III. COLD TOLERANCE
Chilling: When temp remain above freezing i.e. >0°C to <
10-15°C.
Freezing: When temp remains below freezing i.e. <0°C.
Chilling resistance
Chilling sensitive plants are typically tropical plants.
Temperate plants generally tolerate chilling injury.
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33. Effects of chilling on plants
ABA accumulation
Locked open stomata
Poor seed set/ seed formation.
Pollen sterility
Wilting, Chlorosis, necrosis
Stunted growth
Poor seedling establishment
Reduced germination
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34. At subcellular level:
Toxicity due to H2O2 formation
Reduced photosynthesis
Poor chlorophyll synthesis
Reduces membrane stability
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35. Chilling tolerance mechanisms involve
Membrane lipid un-saturation
Reduced sensitivity of photosynthesis
Increased chlorophyll accumulation
Improved germination
Improved fruit/seed set
Pollen fertility
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36. Sources of chilling tolerance:
Late adopted breeding populations e.g. maize
Germplasm
Induced mutants for cold tolerance
Cold tolerant somaclonal variants
Related wild species eg. tomato
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37. b) Freezing resistance
Dormant state is conducive to freezing resistance, while
resistance is rare in actively growing tissue.
As water in plants cool below 0°C, it may either
1) freeze i.e. form ice.
2) super cool with out forming ice.
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38. Effects of freezing stress
1. Ice formation :
Intercellular ice formation:
Intracellular ice formation:
It is most lethal may be due to physical disruption of
sub cellular structure by ice crystals.
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39. 2. Membrane disruption:
Freezing causes disruption and alter the semi
permeable properties of plasma membrane
Loss of solutes from the cells occur
Cells remain plasmolyzed even after thawing
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40. Super cooling:
This is regarded as imp mechanism of freezing
avoidance.
It is possible because internal ice-nucleators are
absent.
In plants water may cool down to -1 to -15°C
In plants cooling of water below 0°C with out ice
crystal formation is called super cooling
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41. Mechanism of freezing resistance
1. Freezing avoidance :
 The ability of plant tissues / or genes to avoid ice formation at sub zero
temperature
Super cooling is a mechanism of freezing avoidance which is controlled
by
 Barriers against external nucleators
 Low moisture contents
 Little or no intercellular space
 Small cell size
 Lack of ice nucleators
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42. 2. Freezing tolerance:
Ability of plants to survive the stress generated by extra
cellular ice formation and to recover and re grow after thawing
Components of freezing tolerance
Cold responsive proteins, e.g. ABA
Cell wall components properties
Plasma membrane stability
Amount of bound water
Osmotic adjustment
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43. Genetic resources for freezing tolerance
Cultivated varieties
Germplasm lines
Induced mutations
Related wild species
e.g. Wheat: Agropyron sp., Rye Oats: Avena sterilis
Transgenes:
e.g. chemical synthesized anti freeze protein gene, ala3 in
tobacco
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44. Selection criteria:
Freezing test in laboratory
Cryo freezing
Osmoregulation
Field survival
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45. Problems in breeding for freezing tolerance:
Breeding work under field conditions is highly
influenced by other environmental factors and
biotic stresses
Due to large G x E interaction field survival
shows poor heritability
Lab tests yet to be developed to screen large
breeding populations
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46. IV. OXIDATIVE STRESS
 Results from conditions promoting the formation of active oxygen species
that damage or kill cells
Environmental factors that cause oxidative stress:
 Intense light that stimulate photoinhibition
 UV light
 wounding
 heat and cold stress
 drought
 heavy metals
 oxidant forming herbicides e.g. Paraquat dichloride
 Air pollution (increased amounts of ozone or sulfur dioxide)
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47. Reactive oxygen species (ROS)
 Formed during certain redox reactions and during incomplete reduction of
oxygen or oxidation of water by the mitochondrial or chloroplast electron
transfer chain.
 e.g. Singlet oxygen, hydrogen peroxide, superoxide anion, hydroxyl and
perhydroxyl radicals
The negative effects of ozone on plants
 Reduced crop yield
 Accelerated senescence
 Reduced growth of shoots and roots
 Leaf injury
 Decreased rates of photosynthesis
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48. Ozone Damage
Oxidative damage to biomolecules
Increases Ca2+ uptake from the apoplasm
Collapses membrane potential
Inhibits H+-pump activity
Increases membrane permeability
Alters ion transport
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49. Resistance to ozone
 Utilizes either avoidance or tolerance
 Avoidance involves physically excluding the pollutant by closing
the stomata, the principal site at which ozone enters the plant
 Tolerance - biochemical responses that induce or activate the
antioxidant defence system and possibly also various repair
mechanisms
Anti-oxidants:
Over expression of certain enzymes such as superoxide dismutase,
ascorbate peroxidase and glutathione reductase has been implicated in
free radical detoxification and scavenging of free radicals under
oxidative stress
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50. Salicylic acid and ethylene
Ozone exposure results in increased amounts of H2O2,
which stimulate the production of SA
Results in a transient increase in the number of transcripts
that encode defence-related secondary metabolites e.g.
phytoalexins, cellular barrier molecules e.g. lignins,
callose, and extensins, PR proteins e.g. (1  3 )  -
glucanase, chitinase, gluthatione S-transferase and
phenylalanine ammonia lyase
Increases ethylene production by inducing increases in
ACC synthase and ACC oxidase gene transcription
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51. Questions ?
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