impact of drought and heat stress on reproductive process of crop plants
TRANSCRIPT
Pavan. RPh. D Scholar
Department of Genetics and Plant BreedingUniversity of Agricultural Sciences
Bengaluru-65Email: [email protected]
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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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Abiotic stress1. 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
Source: Australian Centre for International Agricultural Research
Drought stress
Heat stress
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Abiotic Stress Tolerant Breeding SitesCRIDA,
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"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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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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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
Schematic overview of the reproductive cycle in cereals and the effect of abiotic stress on different stages of reproductive development12
Drought-induced Abscisic Acid (ABA)-dependent plant responses 13
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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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)15
Water deficiency on ovary and female Water 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)16
• 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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• 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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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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Effect of water deficiency on Effect 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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The effect of drought stress (no water for 5 days) at the young microspore stage in wheat
Source: Rudy et al 2011, Plant Science 21
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Effects of heat stress on reproductive phase...?
Alter male fitness
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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25Prasad et al. (1999)
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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27O’Toole (1982)
28Claassen & Shaw (1970)
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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• 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
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
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Climatic conditions at Legon during study period (January-April 2000)
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Effect of water stress on pod and seed yield
35Source: Wahid et al (2007)
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Traits related to tolerance ofhigh 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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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
Advances To Combat
Abiotic Stress
Tolerance
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Conventional Breeding approach
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1.Germplasm evaluation and enhancement
2.Breeding for earliness
3.Breeding for root traits
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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• 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
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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• 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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The Sugar alcohols eg., mannitol
Most important sugar alcohol : Excellent combatable solute
Synthesized by 50 families of angiosperms
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No Benefit Full Benefit
Benefits of OA are stage dependent
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Locating genomic regions associated with components of drought resistance in rice Zhang, et al., 2001
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3.Epicuticular waxes
Quality Quantity
Determines water lossVery 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 understress
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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
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
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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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 64
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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An integrated approach to develop crops for climate change
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Thank U
It i s ea sIt i s ea s y t o y t o wa s t e wa s t e
But d iBut d i f f i c u l t f f i c u l t t o t o p r op ro du c edu c e
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