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Impact of drought and heat stress on reproductive process of crop plants

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Drought and heat stress

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Impact of drought and heat stress on reproductive process of crop plants

  1. 1. Pavan. R Ph. D Scholar Department of Genetics and Plant Breeding University of Agricultural Sciences Bengaluru-65 Email: pavan_55agri@gmail.com 1
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  5. 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 5
  6. 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. 7. Source: Australian Centre for International Agricultural Research Drought stress Heat stress 7
  8. 8. Abiotic Stress Tolerant Breeding Sites CRIDA, 8
  9. 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” 9
  10. 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] 10
  11. 11. Time and intensity of stress • Depending upon time of water stress, flowering is advanced or postponed 11 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. 12. Schematic overview of the reproductive cycle in cereals and the effect of abiotic stress on different stages of reproductive development12
  13. 13. Drought-induced Abscisic Acid (ABA)-dependent plant responses 13
  14. 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) 14
  15. 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) 15
  16. 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) 16
  17. 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) 17
  18. 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) 18
  19. 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 19
  20. 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) 20
  21. 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 21
  22. 22. 22 Effects of heat stress on reproductive phase...? Alter male fitness
  23. 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 23
  24. 24. 24
  25. 25. 25 Prasad et al. (1999)
  26. 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) 26
  27. 27. 27 O’Toole (1982)
  28. 28. 28Claassen & Shaw (1970)
  29. 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) 29
  30. 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 30 Prasad et al. 2006 Stone, 2001
  31. 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) 31
  32. 32. 32 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. 33 Climatic conditions at Legon during study period (January-April 2000)
  34. 34. 34 Effect of water stress on pod and seed yield
  35. 35. 35Source: Wahid et al (2007)
  36. 36. 36
  37. 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 37
  38. 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
  39. 39. 39 The dilemma of plants Water spenders Water Savers
  40. 40. Advances To Combat Abiotic Stress Tolerance 40
  41. 41. Conventional Breeding approach 41 1.Germplasm evaluation and enhancement 2.Breeding for earliness 3.Breeding for root traits
  42. 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 42
  43. 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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  51. 51. 51 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. 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 52
  53. 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 53
  54. 54. The Sugar alcohols eg., mannitol Most important sugar alcohol : Excellent combatable solute Synthesized by 50 families of angiosperms 54
  55. 55. No BenefitFull Benefit Benefits of OA are stage dependent 55
  56. 56. Locating genomic regions associated with components of drought resistance in rice Zhang, et al., 2001 56
  57. 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 57
  58. 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. 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 59
  60. 60. 60 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. 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 61
  62. 62. 62
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  64. 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) 64 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
  65. 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 65
  66. 66. 66 66
  67. 67. 67 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)
  68. 68. 68 Classified into 3 groups 1.Ferns [Selaginella lepidopglla] 3. Angiosperms (17geners) [Xerophyta , Myrothamnus] 2. Bryophytes [Tortula sps]
  69. 69. 69 Taishi et al, 2006
  70. 70. 70 70
  71. 71. 71 71
  72. 72. An integrated approach to develop crops for climate change 72
  73. 73. 73
  74. 74. Thank It is easIt is easy toy to wastewaste But diBut difficultfficult toto proproduceduce 74

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