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Genetic engineering of metabolic pathways in
abiotic stress resistance
Abiotic stresses:
Drought
Salinity
Temperature
Oxidative stress
Chilling
Freezing
High temperature
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Drought Stress
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Drought will be most important abiotic stress in the next 20 years
Water will become scarce and probably wars will start
on this between countries.
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Findings of NCAR (National Centre for Atmospheric Research)
(Published in J. of Hydrometeorology, Dec. 2004)
Area hit by severe drought increased from nearly 12%
in 1970 to 30% in early 2000.
50% of this change is due to global warming rather than decrease
in rainfall or snowfall.
Drought increased in last 30 years : much of Europe, Asia, Western
And South Africa, eastern Australia and Canada.
Down to Earth, Feb 15, 2005
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Water stress
Signal perception
Signal transduction
Gene expression
Gene Products
Functional Proteins Regulatory Proteins
Water channel proteins * Transcription factors
Osmolyte biosynthetic enzymes * Protein KinasesChaperons * Phospholipase C
LEA * 14-3-3protein
Proteinases
Detoxifying enzymes
Stress Tolerance Stress response
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Root to shoot signaling:
a) Message synthesized by roots
b) Role of this message in the devt. of the root itself under stress.
With the help of the message (chemical or electrical) shoots sense
soil drying through roots.
This message instructs shoots to conserve water for useduring later stages of growth.
Closing stomata
Decreasing water loss as a
First line of defence
Decreases transpirational area
by inhibiting leaf expansion
by
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What happens to the ABA when it reaches the stomata
after traveling through the xylems?
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During the last decade, intensive studies at the molecular level have unravelled
the signal intermediates in ABA guard cells drought signaling pathway.
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From the Agriculture perspective we need to develop
desiccation tolerance plants.
WHAT SHOULD BE THEAPPROACH?
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TRANSGENIC APPROACHES TO ENHANCE DROUGHT
TOLERANCE BY INCORPORATING MULTIPLE GENES.
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What is the best source of
these genes?
Answer is
RESURRECTION PLANTS
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What is the Unique feature
of these plants? Can withstand complete dryness
(RWC 1%)
Still viable after rehydration
Full physiological activity resumewithin several hours
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Unique features of these plants
Many survive even at RWC of4% while the lethal RWC of
most crop plants and mesophytes
is 30-50%. [32% Pigeon pea,
50% Soyabean; Ref.Sinclair (1980)]
Can loose over 95% of their
water content survive in their
dried state for prolonged
periods and revive rapidly
when water is available.
Myrothamnus fl abell if oli a
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Craterostigma plantagineum
Hydrated Dried Rehydrated
This and many other studies shows that ABA responsive genes
expressed in dehydrating plants of these species may be responsible
for their amazing desiccation tolerance.
ABA induces desiccation tolerance in Craterostigma calli.
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reflectance
transpiration
Drought tolerance
SUN
cooling
Pest tolerance
PHWL
Epicuticular wax
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Epicuticular wax
Protection from mechanical damage (Walker 1998,Eigenborde 1996)
Primary defence against pathogens(Carver et al 1996)
Site of interaction with insect and microbes
Scatter and reflect light (less heat load,better mesophyll function)
Restricts non-stomatal water loss
Can contribute for drought tolerance and WUE (Samdur et al.,2003)
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VLCFA
Aldehydes
Alkanes
Secondary alcohol
Ketone
Aldehydes
Primary alcohol
Esters
Acyl reductionDecarbonylation
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C 18
C 26
C 28
C 30
C 32
OH
O
Aldehydes
OH
1o Alcohols
Esters
OH
AldehydesO
AlkanesCO2
OH 2 o Alcohols
OKetones
Acyl Reduction Decarbonylation
Fatty acid
Elongation
Cer 1
Cer 6
O
Figure2:The flow chart representing the Epicuticular waxBiosynthetic pathway (Kunst and Samuels,2003)
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March 2005
WXP1- Wax production 1
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Medicago truncatula a novel model plant for legume biological studies.
Small diploid genome
Self fertile
Short life cycle
A large number of Ests have been sequenced
Whole genome sequencing is in progress
Closely related to the worlds most important forage legume alfalfa
It is the fourth most widely grown crop in U.S.
G
http://images.google.co.in/imgres?imgurl=http://www.ccrc.uga.edu/web/personnel/hahn/potted.gif&imgrefurl=http://www.ccrc.uga.edu/web/personnel/hahn/mtimages.htm&h=512&w=768&sz=313&tbnid=4n_Fe0ourr8J:&tbnh=94&tbnw=141&hl=en&start=16&prev=/images%3Fq%3DMedicago%2Btruncatula%2Bplant%26svnum%3D10%26hl%3Den%26lr%3D%26sa%3DG8/14/2019 Abiotic Stress Resistance
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Growth and development
Transgenics were obtained under 35S promoter by Agrobacterium
Mediated Transformation.
Relatively slow growth rate delayed the flowering time
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Trifoliates had more glaucous appearance
Difference in glaucous was more prominent in adaxial side
I t f WXP1 i ti l d ti
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wing coiled crystalline structure decreases
Complemented by increase in density of tubular and plate like
wax crystals
Impact of WXP1 overexpression on cuticular wax production
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Total wax load is significantly higher in transgenic leaves comparedto control.
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PHWL
Top second and third leaf showed decreased water loss
D h l
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T47 is performing better 3days of drought stress
Drought tolerance
WT T47
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Recovery after 10days of drought stress and rewatering
WT T47
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Recovery after 3 cycles of drought- rewatering treatments in green house
WT T47
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Wax Transcription factor
The SHINE Clade of AP2 Domain Transcription Factors
Activates Wax Biosynthesis, Alters Cuticle Properties, and
Confers Drought Tolerance when Overexpressed in
Arabidopsis
Asaph Aharoni,a Shital Dixit,a Reinhard Jetter,b Eveline Thoenes,a Gert van
Arkel,a and Andy Pereiraa
The plant cell, 2004
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Wax composition
Shn 6 fold increase in wax coverage
WT-equal amounts of compounds from both pathway
Shn-partial towards decarbonylation pathway
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15d old seedlings of Arabidopsis
Exposed to 9 to 11d dehydration
Seedlings were watered
Recovery for a week
Checking the drought tolerance
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Salinity StressSalt StressCaused by concentrations greater than that required for
optimum growth of a typical crop plant (1500 ppm or25 mM Na+)
Oceans are the principal sources of salt
99.991% of water is in the oceans where typically Na+ is 460 mMand Cl- is 540 mM.
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Biogeochemical cyclingwater droplets containing salt are carried by wind over landwhere these evaporate and deposit salt onto the soil and increase soil salt content.
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Salinity Impact on Crop Production Worldwide
World Land Surface Area 150 x 106 km2
Salt affected 9 x 106 km2 (6%)
Cultivated Land 15 x 106 km2
*Salt affected 2 x 106 km2 (13%)
Irrigated Land 2.4 x 106 km2
*Salt affected 1.2 x 106 km2 (50%)
*Problem is increasing
Negative Impacts of Salinity on Agriculture
Reduced yields on land that is presently cultivated
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Na+
Na
+external
I A: Suaeda maritima, Atriplex nummularia
I B:Atriplex hastata, Spartina townsendii and sugar beet
II : Cotton, Barley, Tomato, Common bean and soyabean
III : Fruit trees, Avacado, stone fruits etc.,
How does salinity effect plant growth?
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How does salinity effect plant growth?Salinity decreases plant growth, yield and market quality.
1. Short-term effect (minutes to days)
External osmotic effectsReduced leaf expansionLowered stomatal conductance
2. Long-term effects (weeks to months)
Internal ionic effect-specific ion toxicityInjurious conc.of ions:Na+, Cl-, SO4
Chlorosis and Necrosis.
Eventual death.
Non-saline SalineCytosolic Concentration: Na (1-10 mM)
K (100-200 mM)Ratio shifts.
Degree of shift determines the
degree of reduction in growth.
Transgenics Expressing Different Salt Stress Genes
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Osmoprotectants Transporters
Transgenics Expressing Different Salt Stress Genes
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Proline Biosynthesis
Glutamic Acid.
Glutamic gama
semi aldehyde
P5C -Synthase
Pyroline- 5 -Carboxylase
Proline
P5C-Synthase
Stress
induciblepromoter
ABRE
Constitutive
PromoterCamv-35
Introduce to
the plant
Clone
into a
vector(35S-P5CS)(AB P5CS)
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Free proline accumulation in finger millet plants over expressing P5CS
Three weeks old finger millet seedlings were subjected to water deficit
stress for 5 days. The extent of accumulation of free proline were
determined at the end of stress and also one day after re-watering.
0
10
20
30
40
50
60
70
100 % FC 50 % FC 30 % FC Recovery
Proline(mm
ol/gFW)
WT
AB-P5CS
35S-P5CS
Eff t f S lt t S dli th i fi ill t
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Effect of Salt stress on Seedling growth in finger millet
Seeds of wild type and transgenic finger millet over expressing P5CSwere
subjected to salt (NaCl) stress for 5 days. The growth of the P5CStransformed
finger millet seedlings was far better than the untransformed control.
WT AB-P5CS 35S-P5CS
0 mM NaCl
200 mM NaCl
400 mM NaCl
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Phenotype of 6-week old wild type and P5CS seedlings as affected by salinity (200mM NaCl)
stress. Seeds were germinated and maintained on MS medium containing 200mM NaCl. The
plates were kept in a controlled environment at 240C under constant light.
1. Plants
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Choline
CH2OH
CH2
H3C-N+-CH3
CH3
O2 2H2O
2Fd (red) 2Fd (ox)
CMO
CHO
CH2
H3C-N+-CH3
CH3
Betaine
aldehyde
NAD+ NADH
BADH
COO-
CH2
H3C-N+-CH3
CH3
Betaine
2. Escher ichia coli
NAD+ NADH
CDH
CH2OH
CH2
H3C-N+-CH3
CH3
Choline
NAD+ NADH
BADH
CHO
CH2
H3C-N+-CH3
CH3
Betaine
aldehyde
COO-
CH2
H3C-N+-CH3
CH3
Betaine
3. Arhrobacter globif ormisCH2OH
CH2
H3C-N+-CH3
CH3
Choline
2O2 2H2O2
COD
COO-
CH2
H3C-N+-CH3
CH3
Betaine
Biosynthetic pathway of Glycine betaine
synthesis in some natural accumulators.
BETAINES P th i Mi i
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BETAINES
Pathway in plants
Chloine
Betaine aldehyde
Glycine betaine
CMO
BADH
Pathway in Microorganism-
Ar throbacter globiformis
Chloine
Glycine betaine
CODA
Introduce into
plants
Transgenic plants
Cloned into
a vector
Glycine betaine production in transgenic plants:
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Transgene Host plant Accumulation of glycine
betaine
Stress tolerance tested
Barley badh Tobacco
peroxisome
Not tested Not tested
Spinach badh Tobacco
chloroplast
20mmol g-1 FW Not tested
Spinach cmo Tobacco
chloroplast
< 0.05 mmol g-1 FW Not tested
E.colibetB Tobacco
Chloroplast
Not tested Not tested
E.coli betA Tobcco
Cytosol
Not tested Salt
betA/betB Tobacco 0.035 mmol g-1 FW Chilling, Salt
betA Rice 5.0 mmol g-1 FW Drought, Salt
A.globiformiscodA
ArabidopsisChloroplast
1.2 mmol g-1 FW Salt, chilling, Freezing,Heat
CodA Rice 5.3 mmol g-1 FW Salt, chilling
A.pascens cox Arabidopsis 19 mmol g-1 DW Freezing, Salt
cox Brassica napus 13 mmol g-1 DW Drought, Salt
cox Tobacco 13 mmol g-1 DW Salt
I Pl t
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Fructose-6-phosphate
mtlD
Mannitol-1-phosphate
Non-specific phosphatase
Mannitol
NAD
HPr P-HPr
In Plants
In E.coli
(pHPr-phosphorylated heat stable protein)
NADH
Pi
Mannitol biosynthetic pathway in transgenic tobacco
(Mannitol dehydrogenase)
Phenotype of mtlD transgenic finger millet under water deficit stress
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MTLD-1 MTLD-3
WTMTLD-5
yp g g
100%FC 50%FC 30%FC 100%FC 50%FC 30%FC
100%FC 50%FC 30%FC100%FC 50%FC 30%FC
Cyclicitols: (Sugar Alcohols)
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y ( g )
Glucose 6 Phosphate Myoinositol D-Ononitol
D-Pinnitol
IMT1
Trehalose:
Non-reducing disaccharides
TPS1 from yeast---transformed to tobacco.(Trehalose 6 PO4 synthase)
Fructan:Soluble storage polysaccharides
Sucrose FructanLevan sucrase
Transgenic plants engineered to synthesize osmoprotectants other than glycine betaine:
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Osmoprotectant Transgenes Crop plants Accumulation Stress tolerance
Proline
MothbeanP5CS Tobacco
Rice
soyabean
-
-
4 mg g-1 FW
Salt,
Drought, Salt
Osmotic, Heat
Anti-proDH Arabidopsis 0.6 mg g-1 FW Salt
Mannitol E.coli mtlD Arabidopsis
Tobacco
10 mg g-1 FW
m mol g-1 FW
Salt
Salt
Sorbitol Apples6pdh Tobacco
Persimmon 61.5 m mol g-1 FW
Oxidative stress
Salt
Trehalose Yeast tps1 Tobacco
Potato
3.2 m g g-1 FW Drought
Drought
D-Ononitol Ice plant imt1 Tobacco 35 m mol g-1 FW Drought, Salt
Fructans B.subtilis sacB Tobacco
Sugarbeet
0.35 mg g-1 FW
5 mg g-1 FW
Drought
Drought
Glutamine GS2 Rice - Salt, Chilling
Osmotin Osm1-Osm4 Tobacco - Drought, Salt
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Salt stress tolerance of
transgenic plants
http://localhost/var/www/apps/conversion/tmp/scratch_10/salt%20stress%20tolerance%20of%20transgenic%20plants.gifhttp://localhost/var/www/apps/conversion/tmp/scratch_10/salt%20stress%20tolerance%20of%20transgenic%20plants.gifhttp://localhost/var/www/apps/conversion/tmp/scratch_10/salt%20stress%20tolerance%20of%20transgenic%20plants.gifhttp://localhost/var/www/apps/conversion/tmp/scratch_10/salt%20stress%20tolerance%20of%20transgenic%20plants.gif8/14/2019 Abiotic Stress Resistance
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Transgenics Expressing Different Salt Stress Genes
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Osmoprotectants Transporters
g p g
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Intracellular Ca pools
disturbed
Cell elongationCell production
SALT STRESS
Displacement of Ca2+ by Na+ from membranes
Membrane permeabilityNa+ influx
Membrane potential depolarized
H+-ATPase activityH+ efflux
Membrane potential restored
Ca
CaCa
CaCa2+ uptakeK+ efflux
CaCa
Ca
Initial and short-term effects of salt stress on the
plasmalemma of root cells(Cramer et al., 1985)
Ca imparts saline tolerance by increasing K/Na ratio
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Ca imparts saline tolerance by increasing K/Na ratio.
-Both by restricting Na entry as well as by decreasing
K+ efflux.
Control NaCl NaCl + CaCl2
Na (mol.m-3) 3.0 74 44 (40%)K (mol.m-3) 180 132 151 (20%)K/Na ratio 60 1.8 3.4 (50% )
(Ref: Munns, R., 1999)
Maize
Treatment K+ efflux
% of Control
225mM NaCl 68620
225mM NaCl + 10mM
CaCl2
300133
Cotton
(Ref:Cramer, G.R., 1985)
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1 2 3 4 5 6
1: Control 2: 10mM CaCl2 3: 100mM NaCl
4: 100mM NaCl +10mM CaCl2 5: 200mM NaCl 6: 200mM NaCl +10mM CaCl2
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Cellular Homeostasis is the most important aspect and involves osmoregulation,
compartmentation of Na, Calcium singatures and Calcium homeostasis.
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Two good approaches has paid rich dividends for salt tolerance
a) Compartmentalization of the excess Na into the vacuole
b) Restrict the entry of Na by inactivating the
gene HKT1, regulating Na entry.
High Na+ H+
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SOS1
SOS2SOS3 Na
+
Ca2+
?
H2O
Transcriptional &
Post transcriptional
gene regulationH+
V-ATPase
PPase
Vacuole
H+
Na+
SOS2
SOS3
Ca2+
? HKT1
Na+
K+
ACA4
LCA1
Regulation of ion (e.g., Na+ and K+) Homeostasis by the SOS pathway
(Zhu, 2000)
Transport
t i
Mode of
t t
Membrane
l ti
Tools and systems
d f
K:Na
S l ti it
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protein transport location used for
characterization
Selectivity
KAT/AKT
Inward K+
channels
Passive
diffusion
Plasma
membrane
Molecular and
electrophysilology in
planta and inheterologous systems
Highly selective
for K+
HKT1
High affinity K+
transporters
Na+
energizedNot known Molecular and
electrophysilogy in
heterologous systems
Transports both
Na+ and K+
KUP or HAK
High affinity K+
transporter
Not known Not known Molecular and
radioisotopes inheterologous systems
Some Na+
permeability
NSC
Non-Selective
cation channels
Passive
diffusion
Plasma
membrane
Electro physiology in
planta
High Na+
permeability
AtNHX1Na+-H+ exchanger
H+
energized
Vacuole andplasma
membrane
Molecular andradioisotopes in planta
and in heterologous
systems
Not known
LCT1
Low-affinity
cation transporter
Not known Not known Molecular and
radioisotopes in
heterologous systems
Transports both
Na+ and K+
Salient features of Calcium transporters
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ACA4 LCA1 CAX1 CAX2Type of Transporter Ca2+-ATPases Ca2+-ATPases Ca2+/H+
exchangersCa2+/H+
exchangers
Salt induced Yes Yes Not known Not known
mRNA transcripts
under stress
Phenotype changes
when over expressed
Increases
Nil
Normaltransgenic
plants
Increases
Nil
Normaltransgenic plants
Increases
Not known
Transcriptsunder cold stress
Not known
Over expression
studies
Done Done Not done Not done
Effects on over
expression
Salt toleranceincreased
Salt stressincreased
Not known Not known
Other functions Only calciumtransport
Only calciumtransport
Also involved inlow temperature
acclimation
Also involved inmetal transport
Efficiency of
sequestration
Highlyefficient, highaffinity to Ca
Highly efficient,high affinity to
Ca
Highly efficient,High affinity to
Ca
Low efficient,Low affinity to Ca
Two lines of evidence suggest that plant Ca2+-ATPases
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Expression of LCA1 in Tomato Expression of ACA4 in Arabidopsis
gg p
are involved in salt stress adaptation.
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AtNHX1 over-expressionin Brassica
(Salinity tolerance)
X10E1 X10E2 X10E3 WT
WT Transgenic
Expression of Na/H+antiporter
in tomato for salini ty tolerance
SCIENCE VOL. 280 19 JUNE 1998
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Salt
stress
Ionic
stressSOS3SOS2 Ion transporters
e.g. SOS1Ion homeostasis
Homeostasis
Osmotic
stressMAPK
cascade?Osmolytes
Osmotic
homeostasis
Secondary
stresses
e.g. oxidation
Detoxification
Cell division
and expansion
ColdDrought
ABA
CBF/DREBStress proteins
e.g. RD29A
The three aspects of salt tolerance in plants- Homeostasis,
detoxification and growth control (Zhu, 2001).
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Species and genes
Used in transformation
Temperature stress:
http://localhost/var/www/apps/conversion/tmp/scratch_10/species%20and%20genes%20used%20in%20transformation.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_10/species%20and%20genes%20used%20in%20transformation.pdfhttp://localhost/var/www/apps/conversion/tmp/scratch_10/species%20and%20genes%20used%20in%20transformation.pdf8/14/2019 Abiotic Stress Resistance
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physiological and/or structural damage (including plant death) inducedby non-freezing temperatures (0 - 120 C)
physiological and/or structural damage induced by ice formation within
tissues or organs
Chilling stress:
Freezing stress:
metabolic and physiological damage induced by short or long term exposure
to elevated temperature (>400 C)
Heat stress:
Temperature stress:
Effect of temperature on plant growth:
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Cool season crops complete most of their life cycle under cool
conditions, 4 - 120C (broccoli, wheat, bluegrass)
Warm season crops require higher temperatures for optimal
growth , 22 - 300C (tomato, corn, melons)
Perennial crops have adapted mechanisms for coping with
temperature stress.
Optimal growth temperature is a species characteristic.
20C
During slow freezing, ice forms outside the plasmalemma. Thislowers the vapor pressure, and pulls water from the cell until equilibrium
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-20C
-100C
p p , p qis met. This phenomenon is known as freeze dehydration.
Because water leaves the cell until the osmotic pressure insideequilibrates with outside, the organelles and membranes are exposedto high concentrations of salts and other cellular metabolites.
Cells with higher concentrations of protective solutes such as sugarsshrink less to reach equilibrium, and lose less water. The protectivesolutes probably stabilize the membrane and proteins by H-bonding andby lowering the relative concentrations of salts and other damagingmetabolites to which cell organelles are exposed.
During rapid freezing, ice mayform intracellularly because watercannot exit the cell fast enough toequilibrate. Intracellular freezing (inthe absence of cryoprotectants likeDMSO and glycerol) is usually lethalto plant cells, resulting in totalmembrane disruption and collapse of
the cellular organization. Freezing Stress Approach: Mechanisms of freezing resistance.
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During cold acclimation- plant produce a number of cold induced proteins that are
assumed to play a role in the subsequent cold resistance.
About 50 cold induced proteins have been identified in diff. Plant species.
LEA proteins COR genes
(cold responsive)
According to their patterns of expression
There are some examples of the Expression of Cold induced proteins in transgenic plants.
Constitutive expression of Chloroplast targeted COR protein COR15a inArabidopsis
improved freezing tolerance.
Tolerance to heat stress:
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Tolerance to heat stress:
Heat shock proteins (HSPs)
HSP100 HSP90 HSP70 HSP60 SmHSP
Members appear to function as molecular chaperones.
Individual heat shock proteins have been transformed into plants in order to
enhance heat tolerance.
The rapid heat shock response is co-ordinated by a heat-shock transcription factor (HSF)
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Transgenes used to manipulate heat tolerance:
Gene Protein Transgenic plant
AtHSF1 Heat shock transcription factor Arabidopsis
Hsp101 HSP100 class heat-shock protein Arabidopsis
Hsp70 HSP70 class heat-shock protein Arabidopsis
Hsp17.7 SmHSP (small heat-shock protein family) Carrot
TLHS1 Class I smHSP Tobacco
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Secondary effect of abiotic stress:
Production of reactive oxygen species
Drought High Light Heat & Cold
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Wounding
Ozone
Heavymetals
Pathogens
Senescence
Reactive Oxygen
Species
Oxidative stress
Scavenging mechanismAntioxidantsAntioxidants
Enzymes
O2.-Ascorbate-Glutathione cycle (Hlti-Well Asada cycle)
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SOD
Hydrogen peroxide is removed by ascorbate peroxidase and ascorbate is
regenerated by this cycle
APX: Ascorbate Peroxidase
MDHA: Mono DeHydro Ascorbate
DHAR: DeHydro Ascorbate reductase
GR: Glutathione reductase
DHA: DeHydro Ascorbate
Oxidized
Reduced
SOD enzyme family:
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SOD catalyzes the dismutation of superoxide to H2O2 and O2.
SOD is present in most subcelluar compartments of the plant cell and is assumedto play a central role in the defence against oxidative stress.
3 distinct types of SOD: based on metal cofactor.
Cu/Zn SOD
Mn-SOD
Fe-SOD
Cytosol/chloroplast
Mitochondria
Chloroplast
However, they are not regulated coordinately, but independently according to the
degree of oxidative stress experienced in the respective subcelluar compartments.
Transgenes used to engineer tolerance to oxidative stress:Gene Host Stress tolerance
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Ge e os S ess o e ce
Mitochondrial Mn-SOD
Tobacco
Alfalfa chloroplast 2 X increase in SOD
Increased field drought tolerance
Increased freezing toleranceChloroplast Cu/Zn- SOD Tobacco chloroplast 3-15 X increase in SOD
Increased tolerance to high light
and chilling
Cytosolic Cu/Zn-SOD Tobacco cytosol 1.5-6 X increase in SOD
Reduced damage from acuteozone exposure
Fe-SODArabidopsis Tobacco Protected plants from ozone
damage
Apx3 Tobacco Increased protection against
oxidative stressApx1 Arabidopsis Heat tolerance
GST/GPX Tobacco Increase stress tolerance
Nt107 (GST) Tobacco Sustained growth under cold and
salinity stress
NtPox (GPX) Arabidopsis Protects against oxidative stress
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NATURE BIOTECHNOLOGY VOL 23, MARCH 2004
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(Plants exposed to a temp of60C for 2 days and returned to 220C for 5 days)
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( p p y y )
(water withheld for 2 weeks)
(Plants soaked in 600mM NaCl solution for 2 hrs and transferred to pots)
Th b ti t th t b th th DREB1 DNA d th d29A
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These observations suggest that both the DREB1 cDNA and the rd29A
promoter used to improve the dehydration, salt and freezing tolerance of
agriculturally important crops by gene transfer.
The future transgenic approaches is uncertain:
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Reluctance of most consumers to accept transgenically modified food.
Single gene change may not make any difference.
In the future, pyramiding regulatory genes controlling various aspects of
tolerance (i.e., ionic, osmotic homeostasis and damage control) in a single
transgenic plant is expected to yield very high levels of tolerance to salt and
other related stresses.
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