Drought and heat stress

1. Pavan. R
Ph. D Scholar
Department of Genetics and Plant Breeding
University of Agricultural Sciences
Bengaluru-65
Email: pavan_55agri@gmail.com
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5. Water availability in different
continents Vs population
Continents
Available water
(%)
Population
(%)
North America 15 8
South America 26 6
Islands 5 1
Europe 8 13
Africa 11 13
Asia 36 60
Source: Kannada Prabha daily news paper
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6. Abiotic stress
1. Drought
2. High temperature ( above threshold temperature)
3. Cold temperature
 Freezing stress [<0◦
C to -30◦
C] and
 Chilling stress [1 to 6◦
C ]
1. Salinity
2. Flooding
3. Heavy metals (Al, Zn, Cd)
4. Wind
5. Elevated CO2
6. Ozone and UV-B 6

7. Source: Australian Centre for International Agricultural Research
Drought stress
Heat stress
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8. Abiotic Stress Tolerant Breeding Sites
CRIDA,
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9. "Drought stress is a condition of moisture deficit
sufficient to have an adverse effect on
vegetation, animals, and man over a sizeable
area"
Heat stress is defined as “the rise in
temperature beyond a threshold level for a
period of time sufficient to cause irreversible
damage to plant growth and development”
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10. Drought stress Vs heat stress
• Its difficult to delineate between drought and
heat stress
• Drought stress often occurs together with heat
stress in the field
• The regulatory system for both stresses may
have co-evolved [Barnabas et al. 2008]
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11. Time and intensity of stress
• Depending upon time of water stress, flowering
is advanced or postponed
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18◦
C
28◦
C
Days to
Development
of Node (DDN)
Number of
nodes to first
flower (NTFF)
- 8
- 6
- 4
- 2
12 -
10 -
8 -
6 -
4 -
2 -
U shaped response
Vegetative phase is increased

12. Schematic overview of the reproductive cycle in cereals and the effect
of abiotic stress on different stages of reproductive development12

13. Drought-induced Abscisic Acid (ABA)-dependent plant responses 13

14. Effect of water deficiency on
Flower initiation
• Delay in flower induction and inflorescence
development leads to a delay in flowering
(Winkel et al. 1997)
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15. Effect of High temperature on flower initiation
• Temperatures > 30 °C during floret formation cause
complete sterility in wheat
Saini & Aspinall (1982)
• In wheat, the number of kernels per unit area
decreases at a rate of 4% for each degree increase in
mean temperature during anthesis
Fischer (1985)
• In rice, floral abnormalities induced by heat stress (i.e.
stamen hypoplasia and pistil hyperplasia), leading to
spikelet sterility
Takeoka et al. (1991)
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16. Water deficiency on ovary and femaleWater deficiency on ovary and female
gametophyte developmentgametophyte development
• In maize, drought stress leads to delay in female
organ development, while the male inflorescence is
less affected
• in the ABA concentration of the ovary when
compared with irrigated maize plants
• High ABA levels in early reproductive structures may
inhibit cell division and impair floret and then seed
development
Yang et al. (2001a)
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17. • During water deficit, the phloem-mobile dye
carboxyfluorescein is fed to the stems of maize
• They found less movement to the ovary than in
controls supplied with water
• This confirmed that less sugar was delivered by the
phloem to the pedicel during water shortage
Makela et al. (2005)
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18. • The ovaries also displayed less cell wall-bound
invertase activity when the plants were subjected to a
water shortage
Zinselmeier et al. (1995)
• In Arabidopsis reported that, even in harshly stressed
condition plants can allocate sufficient resources into
the female generative organs to produce a few seeds,
ensuring that the genetic line is continued
Sun, et al. (2004)
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19. Effect of elevated temperature on ovary
and
embryo sac development
• Saini & Aspinall (1982) observed that a level of heat
stress that caused male sterility in wheat had no
damaging influence on the functions of female sexual
generation, suggesting that the female gametophyte
had greater heat stress tolerance
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20. Effect of water deficiency onEffect of water deficiency on
pollen developmentpollen development
• Water deficit in the meiotic stage may reduce the grain
set by 35–75% in various cultivars of self-pollinated crops
• In case of wheat, drought stress results in increased
pollen sterility due to abnormalities in microsporogenesis
and microgametogenesis
Saini et al. (1984)
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21. The effect of drought stress (no water for 5 days)
at the young microspore stage in wheat
Source: Rudy et al 2011, Plant Science
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Effects of heat stress on
reproductive phase...?
Alter male
fitness

23. In Datura (Buchholz and Blakeslee, 1927) where
pollen tube growth rate increased linearly by a factor
of 4.5 from 11 ◦C to 33 ◦C (from 1.28 mm/h to 5.86
mm/h). Pollen tube growth rate increased
In Datura (Buchholz and Blakeslee, 1927) where
pollen tube growth rate increased linearly by a factor
of 4.5 from 11 ◦C to 33 ◦C (from 1.28 mm/h to 5.86
mm/h). Pollen tube growth rate increased
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Prasad et al. (1999)

26. Effect of drought stress on fertilization
• In maize, abortion is highly dependent on the
timing of water stress: low water availability
before pollination resulted in abortion even if
sufficient water was available at the time of
pollination
(Westgate & Boyer 1986)
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O’Toole (1982)

28. 28Claassen & Shaw (1970)

29. Effect of heat stress on fertilization
• In wheat, High-temperature stress (>30 °C) from
early meiosis to pollen maturity has a damaging
effect on the viability of pollen grains, resulting in
a failure of fertilization, and thus in a reduction in
seed set
(Saini & Aspinall,1982)
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30. • Increased temperature over the mid-anthesis period
decreased the grain number per ear at maturity in spring
wheat
Ferris et al. (1998)
• Sterility is caused by poor anther dehiscence and low pollen
production, and hence low number of germinating pollen
grains on the stigma
• In maize, reduction in seed set occurs at temperatures
higher than 38 °C mainly because of a reduction in pollen
germination ability and pollen tube elongation
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Prasad et al. 2006
Stone, 2001

31. Grain Filling Under Heat And Drought
• Large yield losses in cereals because of reduction in
starch accumulation
• In wheat, drought (20 days at endosperm cell division)
resulted in 30–40% lower endosperm cell number, and
the number of small starch granules per cells was also
reduced by 45%
(Nicolas et al. 1985)
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Crops: Cowpea, groundnut and Bambara groundnut
Treatment:
1. Liberal watering until maturity
2. Seven-day dry cycle from 41 to 47 DAP
3. Two dry cycles: from 41 to 47 DAP followed by
resumed liberal watering and another dry cycle from
54 to 59 DAP

33. 33
Climatic conditions at Legon during study period
(January-April 2000)

34. 34
Effect of water stress on pod and seed yield

35. 35Source: Wahid et al (2007)

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37. Traits related to tolerance of
high temperature stress in rice
Plant architecture: The panicle is surrounded
by many leaves
Time of flowering and anthesis
Length of anther
Size of basal pore
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38. Strategies adapted by all forms of life
to mitigate stress
Tolerance
Avoidance
A boring lecture
Escape
Plant responses to water deficit
Ability to complete life cycle
during wet periods
Ability to maintain
tissue hydration.
Eg: Leaf rolling,
Epicuticular Wax,
Deep roots Ability to function
while dehydration 38

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The dilemma of plants
Water
spenders
Water
Savers

40. Advances To Combat
Abiotic Stress
Tolerance
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41. Conventional Breeding approach
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1.Germplasm evaluation and enhancement
2.Breeding for earliness
3.Breeding for root traits

42. Molecular Breeding approach
• Genome sequence of many crops available now
• Next generation sequencing: cheap and quick
• Approaches: 1. Identification of QTLs
• Until recently linkage mapping
• Nested association mapping
2. Introgression of QTLs: MABC
Very few examples for drought and heat tolerance
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43. • In this study, the genetic bases of DT and DA at
reproductive stage in rice were analyzed using a 180
RIL’s of F9/F10 generation from a cross between an indica
lowland and a tropical japonica upland cultivar
• 21 traits measuring fitness, yield, and the root system
were investigated
• 9 traits are collected above ground level and other 12
are root traits 43

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1. Water use efficiency (WUE): Increasing the yield or
biomass per unit of water availability
Unit: (g DM/Kg water used)
WUE can be increased either
by decreasing transpiration or
by increasing photosynthetic rate
By using high wax line, we can achieved 2-3 fold increase
in WUE
PHYSIOLOGICAL APPROACH

52. 2. Osmotic adjustment
net increase in intercellular
solutes in response to water
stress, which allows turgor
maintenance at lower water
potential
Target : Gene encoding rate
limiting enzymes in
biosynthetic pathway of
various osmolytes like
Proline, mannitol etc
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53. • Proline : Amino acid
• Targeted P5C5 gene
• Codes for rate limiting enzyme in Proline biosynthesis
pathway
• P5C5 gene from Vigna (cowpea) overexpressed in
tobacco
• Result: P5C5 transgenics highly tolerant to stress
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54. The Sugar alcohols eg., mannitol
Most important sugar alcohol : Excellent combatable solute
Synthesized by 50 families of angiosperms
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55. No BenefitFull Benefit
Benefits of OA are stage
dependent
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56. Locating genomic regions associated with components of
drought resistance in rice Zhang, et al., 2001
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57. 3.Epicuticular waxes
Quality Quantity
Determines water loss
Very Long Chain Fatty Acid products generated in
epidermis are used for synthesis of other wax components
EW manipulation can be viable option to increase stress
tolerance
Waxes increases under
stress
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58. Wax encoding genes identified
Gene Site of action
CER 5 Codes for ABC transporter involved in wax transporter from inner to
outer surface of epidermis
CUT 1 90 % identical to CER-5
WAX 2 32 % identity with CER-1 and involved in cuticle membrane
development
WIN 1 Wax inducer 1 from Arabidopsis, activated several genes involved in
decarbonyalation pathway of wax production
SHINE 1 Same as WIN-1
WXP-1 Wax production 1 from Medicago trunculata,
Activates several genes involved in acyl reduction pathway of wax
production 58

59. Asaph et al., 2004 Plant
Cell
Increased wax synthesis improved drought tolerance
Evidences
Transcriptional factors regulating wax biosynthesis
SHINE/WIN1-AP2 ERF Transcription factorsSHINE/WIN1-AP2 ERF Transcription factors
Potential candidate genesPotential candidate genes
SHINE, CERSHINE, CER
WT WXP1 transgenics
3d after drought stress
Zhang et al., 2005, Plant journal
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1. Osmoprotectants: involves the upregulation of compatible solutes
(osmolytes) that function primarily to maintain cell turgor
• Compatible solutes are low molecular weight, highly soluble
compounds that are usually nontoxic at high cellular
concentrations
• The three major groups of compatible solutes are
Amino acids (such as proline),
Quaternary amines (such as glycine betaine (GlyBet),
polyamines, and dimethylsulfonioproprionate),
Polyol/Sugars (such as mannitol, galactinol, and trehalose
Molecular Responses

61. 2. Late embryogenesis abundent proteins
• LEA proteins are produced in response to dehydration stress
• Functions:
 Protection of cytosolic structures,
 Ion sequestration,
 Protein renaturation,
 Transport of nuclear targeted proteins,
 Prevention of membrane leakage,
 Protein stabilization
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64. 3. Heat shock protein genes
• Typical response to heat stress is a decrease in
the synthesis of normal proteins, accompanied
by an accelerated transcription and translation
of new proteins known as heat shock proteins
(HSPs)
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Protein class Size (kDa) Location
HSP100 100-114 cytoplasm
HSP90 80-94 cytoplasm, ER
HSP70 69-71 ER, cytoplasm, mitochondria
HSP60 10-60 chloroplasts, mitochondria
smHSP 15-30 cytoplasm, chloroplast, ER, mitochondria
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65. 4. Transcription factors validated under field conditions4. Transcription factors validated under field conditions
AtDREB1A – Groundnut, Rice, Potato, Pigeon pea
GCP support (CGIAR/ICRISAT/JIRCAS/IRRI/University of Tsukuba)
AtDREB1A – Groundnut, Rice, Potato, Pigeon pea
GCP support (CGIAR/ICRISAT/JIRCAS/IRRI/University of Tsukuba)
HsfA1 – tomato (Nover’ group)HsfA1 – tomato (Nover’ group)
OsDREB 1A – Rice (Yamaguchi Shinozaki and Shinozaki, 2004)OsDREB 1A – Rice (Yamaguchi Shinozaki and Shinozaki, 2004)
Shinozaki, 2004
DREB 1A – Soyabean, Few vegetables (AVRDC)DREB 1A – Soyabean, Few vegetables (AVRDC)
SNAC – Rice (Xiong et al., 2006)SNAC – Rice (Xiong et al., 2006)
NF-Y – Maize (Nelson et al., 2007)NF-Y – Maize (Nelson et al., 2007)
Bacterial RNA chaperon (CspA)-maizeBacterial RNA chaperon (CspA)-maize
Plant nuclear factor Y (NF-Y)Plant nuclear factor Y (NF-Y)
confer drought tolerance in maizeconfer drought tolerance in maize
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Genetic Engineering approach
Can loose over 95%
water content and
survive for prolonged
periods
Survive at a RWC of
4%, while the lethal
RWC of most of the
crop plants and
mesophytes is 30-50%
[32 % Pegion pea, 50% Soyabean ]
Sinclari (1980)

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Classified into 3 groups
1.Ferns [Selaginella lepidopglla]
3. Angiosperms (17geners)
[Xerophyta , Myrothamnus]
2. Bryophytes [Tortula sps]

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Taishi et al, 2006

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72. An integrated approach to develop crops
for climate change
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74. Thank
It is easIt is easy toy to
wastewaste
But diBut difficultfficult
toto proproduceduce
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