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STRESS BIOCHEMISTRY
Introduction
Environmental stresses represent the most limiting
factors for agricultural productivity. Crop yields fall because
plants usually grow under environmental stress. Such
stress is both biotic and abiotic.
 Biotic (Pathogens, Herbivores )
 Abiotic stress (Heat, Cold, Drought, Salt, Wind, Oxidative,
Anaerobic, Heavy metals, Wounding, Nutrient deprivation,
Excessive light )
 Agricultural productivity is severely affected by soil salinity
because salt levels that are harmful to plant growth affect
large terrestrial areas of the world
 Salt-affected soils covers over 400 million hectares, which
is over 6% of the world land area (FAO report)
 Current 230 million ha of irrigated land, 45 million ha are salt-
affected (19.5 %) and of the 1,500 million ha under
dryland agriculture, 32 million are salt-affected to varying
degrees (2.1 %)
 In Tamil Nadu, about around 7.0 million ha of cultivable land is
reeling under salt stress
State Area under saline/alkaline soils (million ha)
Uttar pradesh 1.280
Gujarat 1.200
West bengal 0.840
Rajasthan 0.720
Punjab 0.680
Maharashtra 0.528
Haryana 0.520
Karnataka 0.400
Orissa 0.400
Madhya pradesh 0.240
Andhra pradesh 0.024
Delhi 0.016
Kerela 0.016
Tamil nadu 6.872 (or about 7 million hectares)
The extent of saline and alkali soils in India
Salinity Stress
This is due to the following soil characteristics:
i. High soil pH (less than 8.5)
ii. High electrical conductivity - EC value (more than 4.0 dS m-1)
(deciSeimens per meter)
i. Low ESP - Exchangeable Sodium Percentage (less than 15.0)
ii. Predominantly due to excessive content of chlorides and
sulphates of sodium
Types of salt stress
Following soil features are found to cause the sodicity
stress in plants
i. High soil pH (more than 8.5)
ii. Low EC value (less than 1.0 dS m-1)
iii. High Exchangeable Sodium Percentage (more than 15.0)
iv. Predominantly due to excessive content of carbonate and
bicarbonates of sodium
Sodicity Stress
Classes of saline and alkali soils
Type of salinity/
Property
SALINE SOILS SALINE-ALKALI
SOILS
NON SALINE
ALKALI OR
SODIC SOILS
pH < 8.5 < 8.5 > 8.5
EC
(mmhos/cm)
> 4.0 > 4.0 < 4.0
ESP < 15 > 15 > 15
Other properties white
encrustation on
the surface
- surface soil is
discolored and
black
Based on the reaction of plants to salt stress, the mesophytes
are classified into following categories:
 Halophytes:
These plants can grow in saline environment and are found to
be tolerant to salt stress. Depending upon the degree of
tolerance, there are two types of halophytes.
1. Euhalophytes
They are extremely tolerant to salt stress (eg. Atriplex).
2. Oligohalophytes (Facultative halophytes)
These plants are moderately tolerant to salty environment (eg.
salt tolerant crop species)
Classification of plants under salt stress
 Glycophytes
These plants can not grow in the presence of salts in the
growing medium. They are susceptible to salt stress.
Almost all cultivated salt-sensitive crop species come
under this category only.
Besides, depending upon the nature of accumulation of sodium
content, the plants are classified as:
Sodium accumulator: These plants will absorb more of
sodium form the external medium and accumulate the excess
content in the stem portions without being translocated to other
parts of the plant.
Sodium avoider: Under this category, the plants will avoid the
uptake of sodium form the soil preferably due to excessive
uptake of potassium, calcium etc.
1. Primary effects
2. Secondary effects
1. Primary Effects:
These effects are again sub-divided into:
Direct Effects:
This is mainly due to accumulation of specific ions. As a result,
osmotic pressure is increased; availability of physiological
water is reduced causing "Physiological Drought".
.
Salt stress effects on plants
Indirect Effects:
This is mainly due to disturbances in the metabolic activities
of the plants causing inhibition in growth and development
of plants. There is a greater penetration and accumulation of
larger quantities of Na+ in the form of Cl-, CO3
- or HCO3
- etc.
Secondary Effects
Causing nutrient deficiency
Excessive accumulation of Na+ causes deficiencies of certain
essential elements such as N, P, K, Ca, Mg, Zn, Fe etc. thus causing
derangement of metabolism in the plants
Salinity inhibit plant growth for two reasons
 Presence of salt in the soil solution reduces the ability of the
plant to take up water, and this leads to reductions in the
growth rate (osmotic or water-deficit effect of salinity )
 Excessive amounts of salt enter the plant in the transpiration
stream there will be injury to cells in the transpiring leaves and
this may cause further reductions in growth (salt-specific or
ion-excess effect of salinity )
Variation in Salt Tolerance between Species
Number of agricultural horticultural crops affected by salinity
 Degree of responses vary (depending on salt tolerance
mechanism)
Examples:
 Wheat is one of the more salt-tolerant crop species, and many
cultivars that have been selected for yield in water-limited
conditions do not suffer a 50% reduction in biomass until
salinities reach 15 dS/m (approximately 150 mM NaCl)
 Rice is more salt-sensitive, and many cultivars suffer a 50%
reduction in growth at half this concentration of salts
 All living organisms in dry and saline environments is to
maintain water content this is achieved by solute accumulation
which lowers solute potential
 The solutes accumulated in the cytoplasm must be non-toxic
(compatible) with respect to metabolic processes (they should not
interfere with protein structure or function when present at high
concentration)
 This osmotic adjustment is a fundamental adaptive response
of plant cells to salinity.
 This process is necessary for their survival and growth under
saline conditions
A positive turgor is indispensable for expansion growth of
cells and stomatal openings in plants
A decrease in water potential due to soil salinity causes
osmotic stress that leads to turgor loss
Plants have evolved an osmotic adjustment (active solute
accumulation) mechanism that maintains water uptake and turgor
under osmotic stress conditions
Sodium Compartmentation
 Osmotic adjustment, plants use inorganic K+ and/or
synthesize organic compatible solutes such as proline, betaine,
polyols and soluble sugars
 Salinization causes relatively little change in vacuolar and
cytoplasmic K+ in leaves. Na+ and C1- accumulated mainly in the
vacuole and Betaine mainly in the cytoplasm (chloroplasts and
cytosol)
 The vacuole occupies about 90% of the cell volume and the
chloroplast and cytosol about 5% each. Hence osmotic adjustment
of the bulk of the cell water is achieved with Na+ and C1- which are
readily available from the salinized growing medium but are toxic
to metabolism
 Glycine-betaine or other osmoprotectants which are non-toxic
but energetically expensive is useful for osmotic adjustment only
in the crucial metabolic compartments.
 Vacuolar sequestration of Na is an important and cost-effective
strategy for osmotic adjustment that also reduces the Na
concentration in the cytosol
 Na sequestration into the vacuole depends on expression and
activity of Na/H antiporters as well as on H –ATPase
 These phosphatases generate the necessary proton gradient
required for activity of Na/H antiporters
Sequestration of Sodium
Na+
K+
H+
Na+
Na+
H+
H+
H+
ATP
PPi
H+
ATP
Tonoplast
Vacuole
Plasma Membrane
V-ATPase
P-ATPase
V-PPase
Na+/H+ antiport
K+/Na+ ratio
K+/Na+ selectiveVICs
K+
High-affinity K+
transporters
Na+ uptake/extrusion in the plant cell
Na+
Na+
Growth inhibition
 In most of the mesophytes, salt level of more than 50mM
often causes decline in the growth of plants
 Both root and shoot growth is affected
 Biomass production is decreased by 50% than the normal
environment
 This reduction is mainly due to several physiological
aberrations induced by the salt stress
Physiological and Biochemical Changes
Pigments
 There was a reduction in the leaf chlorophyll content from 8.2
to 32.8 per cent
 Hill reaction of photosynthesis is affected severely in salt
stress leading to decline in the production of energy rich ATP
molecules and thus there was a close correlation between salt
tolerance and the rate of Hill reaction in the chloroplast
Carotene contents increased and neoxanthine content
decreased in salt resistant varieties, while in the susceptible
varieties, neoxanthine content increased but the carotene
content did not change
 However, adverse effect of salinity was expressed mainly
through its effect on photosynthesis rather than decrease in the
chlorophyll level.
 Inhibition of nitrogen assimilation is reported in several
cases under salt stress
 Inhibition of nitrate reductase (NRase), the enzyme reducing
nitrate to nitrite, is the most sensitive reaction in nitrate
assimilation process as reported in beans and spinach when
grown under salt affected soils
 Other enzymes involved in ammonium assimilation pathway
are also inhibited by salt stress
Nitrogen and Protein metabolism
 Protein content decreased due to salinity stress. Soluble
protein content is also found to be decreasing in salt
stressed plants
 A large number of protein revealed to show up / down
regulation due to salt stress. The proteins, which are up-
graded by the stress condition, are refereed as "Stress
Proteins“
Reduced uptake of K+ and other monovalent cations has been
reported under salt stress and also inhibition of mineral
transport from root to shoot is common
This may be due to the competitive effects of Na+ and Cl- with
other essential elements. Contents of P, Mg, Ca, Zn, B, Fe and
Cu are also found decreasing due to salt stress
Mineral uptake and transport
Enzyme activities
The activities of free radical scavenging enzymes such as
catalase, peroxidase and Super Oxide Dismutase (SOD) are
known to increase in the tolerant genotypes under salt
stress. This helps in the removal of excessive accumulation
of free radicals thus averting the membrane damage due to
the stress.
 There is a five-fold reduction in the content of IAA
observed under salinity stress in plants
 Similarly, the levels of gibberellins and cytokinins are also
found to decrease due to salinity stress
 Whereas ABA and ethylene increase under the salt stress,
which will induce early on-set of senescence (yellowing due
to ageing) in crops thus reducing yielding ability of crops
Growth Regulators
Compatible Osmolytes
osmotic adjustment may be energetically more favorable than biosynthesis of
organic osmolyte under osmotic stresses, many plants accumulate organic
osmolytes to tolerate osmotic stresses
STRESS
Physiological and
developmental
response
Stress
recognition
Signal
transduction
Gene expression
Altered cell
metabolism
These osmolytes include proline, betaine, polyols, sugar
alcohols, and soluble sugars
The range of compounds participating in osmotic adjustment is
usually qualitatively the same as that accounting for solute
potential in nonstressed tissue
Glycine betaine and trehalose act as osmoprotectants by
stabilizing quaternary structures of proteins and highly ordered
states of membranes
Proline serves as a storage sink for carbon and nitrogen and a
free-radical scavenger. It also stabilizes subcellular structures
(membranes and proteins), and buffers cellular redox potential
under stress
 The physiological changes of the adaptation process are
accompanied by increases or decreases in a relatively small set of
cellular proteins, some of which have been purified and
characterized
 The most extensively studied protein of this class has been
referred to as osmotin (26 kDa)
 rab 21 gene from rice which encode a gly-thr rich protein. rab
21 is not an integral membrane protein
 Sal T mRNA accumulates very rapidly in sheaths and roots of
rice
Stress-induced proteins
Conclusion
Understanding the biosynthesis, transport, roles of osmoprotectants
during stress and the signaling events that regulate stress-induced
accumulation is vital in developing plants for stress-tolerance
Vacuole occupies Na+ and Cl- about 90% of the cell volume and the
chloroplast and cytosol about 5% each and are toxic to metabolism
Glycinebetaine or other osmoprotectants which are non-toxic but
energetically expensive is useful for osmotic adjustment only in the
crucial metabolic compartments
It is important to use Molecular approaches to study the available
transgenic plants to identify the metabolic pathways influenced due to
changes in osmoprotectant level

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2. Abiotic- Salt stress.ppt

  • 2. Introduction Environmental stresses represent the most limiting factors for agricultural productivity. Crop yields fall because plants usually grow under environmental stress. Such stress is both biotic and abiotic.  Biotic (Pathogens, Herbivores )  Abiotic stress (Heat, Cold, Drought, Salt, Wind, Oxidative, Anaerobic, Heavy metals, Wounding, Nutrient deprivation, Excessive light )
  • 3.  Agricultural productivity is severely affected by soil salinity because salt levels that are harmful to plant growth affect large terrestrial areas of the world  Salt-affected soils covers over 400 million hectares, which is over 6% of the world land area (FAO report)  Current 230 million ha of irrigated land, 45 million ha are salt- affected (19.5 %) and of the 1,500 million ha under dryland agriculture, 32 million are salt-affected to varying degrees (2.1 %)  In Tamil Nadu, about around 7.0 million ha of cultivable land is reeling under salt stress
  • 4. State Area under saline/alkaline soils (million ha) Uttar pradesh 1.280 Gujarat 1.200 West bengal 0.840 Rajasthan 0.720 Punjab 0.680 Maharashtra 0.528 Haryana 0.520 Karnataka 0.400 Orissa 0.400 Madhya pradesh 0.240 Andhra pradesh 0.024 Delhi 0.016 Kerela 0.016 Tamil nadu 6.872 (or about 7 million hectares) The extent of saline and alkali soils in India
  • 5. Salinity Stress This is due to the following soil characteristics: i. High soil pH (less than 8.5) ii. High electrical conductivity - EC value (more than 4.0 dS m-1) (deciSeimens per meter) i. Low ESP - Exchangeable Sodium Percentage (less than 15.0) ii. Predominantly due to excessive content of chlorides and sulphates of sodium Types of salt stress
  • 6. Following soil features are found to cause the sodicity stress in plants i. High soil pH (more than 8.5) ii. Low EC value (less than 1.0 dS m-1) iii. High Exchangeable Sodium Percentage (more than 15.0) iv. Predominantly due to excessive content of carbonate and bicarbonates of sodium Sodicity Stress
  • 7. Classes of saline and alkali soils Type of salinity/ Property SALINE SOILS SALINE-ALKALI SOILS NON SALINE ALKALI OR SODIC SOILS pH < 8.5 < 8.5 > 8.5 EC (mmhos/cm) > 4.0 > 4.0 < 4.0 ESP < 15 > 15 > 15 Other properties white encrustation on the surface - surface soil is discolored and black
  • 8. Based on the reaction of plants to salt stress, the mesophytes are classified into following categories:  Halophytes: These plants can grow in saline environment and are found to be tolerant to salt stress. Depending upon the degree of tolerance, there are two types of halophytes. 1. Euhalophytes They are extremely tolerant to salt stress (eg. Atriplex). 2. Oligohalophytes (Facultative halophytes) These plants are moderately tolerant to salty environment (eg. salt tolerant crop species) Classification of plants under salt stress
  • 9.  Glycophytes These plants can not grow in the presence of salts in the growing medium. They are susceptible to salt stress. Almost all cultivated salt-sensitive crop species come under this category only.
  • 10. Besides, depending upon the nature of accumulation of sodium content, the plants are classified as: Sodium accumulator: These plants will absorb more of sodium form the external medium and accumulate the excess content in the stem portions without being translocated to other parts of the plant. Sodium avoider: Under this category, the plants will avoid the uptake of sodium form the soil preferably due to excessive uptake of potassium, calcium etc.
  • 11. 1. Primary effects 2. Secondary effects 1. Primary Effects: These effects are again sub-divided into: Direct Effects: This is mainly due to accumulation of specific ions. As a result, osmotic pressure is increased; availability of physiological water is reduced causing "Physiological Drought". . Salt stress effects on plants
  • 12. Indirect Effects: This is mainly due to disturbances in the metabolic activities of the plants causing inhibition in growth and development of plants. There is a greater penetration and accumulation of larger quantities of Na+ in the form of Cl-, CO3 - or HCO3 - etc.
  • 13. Secondary Effects Causing nutrient deficiency Excessive accumulation of Na+ causes deficiencies of certain essential elements such as N, P, K, Ca, Mg, Zn, Fe etc. thus causing derangement of metabolism in the plants
  • 14. Salinity inhibit plant growth for two reasons  Presence of salt in the soil solution reduces the ability of the plant to take up water, and this leads to reductions in the growth rate (osmotic or water-deficit effect of salinity )  Excessive amounts of salt enter the plant in the transpiration stream there will be injury to cells in the transpiring leaves and this may cause further reductions in growth (salt-specific or ion-excess effect of salinity )
  • 15. Variation in Salt Tolerance between Species Number of agricultural horticultural crops affected by salinity  Degree of responses vary (depending on salt tolerance mechanism) Examples:  Wheat is one of the more salt-tolerant crop species, and many cultivars that have been selected for yield in water-limited conditions do not suffer a 50% reduction in biomass until salinities reach 15 dS/m (approximately 150 mM NaCl)  Rice is more salt-sensitive, and many cultivars suffer a 50% reduction in growth at half this concentration of salts
  • 16.  All living organisms in dry and saline environments is to maintain water content this is achieved by solute accumulation which lowers solute potential  The solutes accumulated in the cytoplasm must be non-toxic (compatible) with respect to metabolic processes (they should not interfere with protein structure or function when present at high concentration)  This osmotic adjustment is a fundamental adaptive response of plant cells to salinity.  This process is necessary for their survival and growth under saline conditions
  • 17. A positive turgor is indispensable for expansion growth of cells and stomatal openings in plants A decrease in water potential due to soil salinity causes osmotic stress that leads to turgor loss Plants have evolved an osmotic adjustment (active solute accumulation) mechanism that maintains water uptake and turgor under osmotic stress conditions Sodium Compartmentation
  • 18.  Osmotic adjustment, plants use inorganic K+ and/or synthesize organic compatible solutes such as proline, betaine, polyols and soluble sugars  Salinization causes relatively little change in vacuolar and cytoplasmic K+ in leaves. Na+ and C1- accumulated mainly in the vacuole and Betaine mainly in the cytoplasm (chloroplasts and cytosol)
  • 19.  The vacuole occupies about 90% of the cell volume and the chloroplast and cytosol about 5% each. Hence osmotic adjustment of the bulk of the cell water is achieved with Na+ and C1- which are readily available from the salinized growing medium but are toxic to metabolism  Glycine-betaine or other osmoprotectants which are non-toxic but energetically expensive is useful for osmotic adjustment only in the crucial metabolic compartments.
  • 20.  Vacuolar sequestration of Na is an important and cost-effective strategy for osmotic adjustment that also reduces the Na concentration in the cytosol  Na sequestration into the vacuole depends on expression and activity of Na/H antiporters as well as on H –ATPase  These phosphatases generate the necessary proton gradient required for activity of Na/H antiporters Sequestration of Sodium
  • 21. Na+ K+ H+ Na+ Na+ H+ H+ H+ ATP PPi H+ ATP Tonoplast Vacuole Plasma Membrane V-ATPase P-ATPase V-PPase Na+/H+ antiport K+/Na+ ratio K+/Na+ selectiveVICs K+ High-affinity K+ transporters Na+ uptake/extrusion in the plant cell Na+ Na+
  • 22. Growth inhibition  In most of the mesophytes, salt level of more than 50mM often causes decline in the growth of plants  Both root and shoot growth is affected  Biomass production is decreased by 50% than the normal environment  This reduction is mainly due to several physiological aberrations induced by the salt stress Physiological and Biochemical Changes
  • 23. Pigments  There was a reduction in the leaf chlorophyll content from 8.2 to 32.8 per cent  Hill reaction of photosynthesis is affected severely in salt stress leading to decline in the production of energy rich ATP molecules and thus there was a close correlation between salt tolerance and the rate of Hill reaction in the chloroplast Carotene contents increased and neoxanthine content decreased in salt resistant varieties, while in the susceptible varieties, neoxanthine content increased but the carotene content did not change  However, adverse effect of salinity was expressed mainly through its effect on photosynthesis rather than decrease in the chlorophyll level.
  • 24.  Inhibition of nitrogen assimilation is reported in several cases under salt stress  Inhibition of nitrate reductase (NRase), the enzyme reducing nitrate to nitrite, is the most sensitive reaction in nitrate assimilation process as reported in beans and spinach when grown under salt affected soils  Other enzymes involved in ammonium assimilation pathway are also inhibited by salt stress Nitrogen and Protein metabolism
  • 25.  Protein content decreased due to salinity stress. Soluble protein content is also found to be decreasing in salt stressed plants  A large number of protein revealed to show up / down regulation due to salt stress. The proteins, which are up- graded by the stress condition, are refereed as "Stress Proteins“
  • 26. Reduced uptake of K+ and other monovalent cations has been reported under salt stress and also inhibition of mineral transport from root to shoot is common This may be due to the competitive effects of Na+ and Cl- with other essential elements. Contents of P, Mg, Ca, Zn, B, Fe and Cu are also found decreasing due to salt stress Mineral uptake and transport
  • 27. Enzyme activities The activities of free radical scavenging enzymes such as catalase, peroxidase and Super Oxide Dismutase (SOD) are known to increase in the tolerant genotypes under salt stress. This helps in the removal of excessive accumulation of free radicals thus averting the membrane damage due to the stress.
  • 28.  There is a five-fold reduction in the content of IAA observed under salinity stress in plants  Similarly, the levels of gibberellins and cytokinins are also found to decrease due to salinity stress  Whereas ABA and ethylene increase under the salt stress, which will induce early on-set of senescence (yellowing due to ageing) in crops thus reducing yielding ability of crops Growth Regulators
  • 29. Compatible Osmolytes osmotic adjustment may be energetically more favorable than biosynthesis of organic osmolyte under osmotic stresses, many plants accumulate organic osmolytes to tolerate osmotic stresses STRESS Physiological and developmental response Stress recognition Signal transduction Gene expression Altered cell metabolism
  • 30. These osmolytes include proline, betaine, polyols, sugar alcohols, and soluble sugars The range of compounds participating in osmotic adjustment is usually qualitatively the same as that accounting for solute potential in nonstressed tissue Glycine betaine and trehalose act as osmoprotectants by stabilizing quaternary structures of proteins and highly ordered states of membranes Proline serves as a storage sink for carbon and nitrogen and a free-radical scavenger. It also stabilizes subcellular structures (membranes and proteins), and buffers cellular redox potential under stress
  • 31.  The physiological changes of the adaptation process are accompanied by increases or decreases in a relatively small set of cellular proteins, some of which have been purified and characterized  The most extensively studied protein of this class has been referred to as osmotin (26 kDa)  rab 21 gene from rice which encode a gly-thr rich protein. rab 21 is not an integral membrane protein  Sal T mRNA accumulates very rapidly in sheaths and roots of rice Stress-induced proteins
  • 32. Conclusion Understanding the biosynthesis, transport, roles of osmoprotectants during stress and the signaling events that regulate stress-induced accumulation is vital in developing plants for stress-tolerance Vacuole occupies Na+ and Cl- about 90% of the cell volume and the chloroplast and cytosol about 5% each and are toxic to metabolism Glycinebetaine or other osmoprotectants which are non-toxic but energetically expensive is useful for osmotic adjustment only in the crucial metabolic compartments It is important to use Molecular approaches to study the available transgenic plants to identify the metabolic pathways influenced due to changes in osmoprotectant level