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Salinity stress tolerance in plants master seminar



Abiotic stress resistance @ sid

Abiotic stress resistance for plants

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Abiotic stress resistance @ sid

  2. 2. OUTLINE  Introduction  Drought tolerance  Salt tolerance  Cold tolerance  Oxidative stress tolerance
  3. 3. What’s in name? Stress: Factors of environment interfering the complete expression of genotypic potential. Abiotic stress: The negative impact of non-living factors on the living organisms in a specific environment. Abiotic stress factors or stressors are naturally occurring, often intangible factors The four major abiotic stresses: drought , salinity, temperature and heavy metals, cause drastic yield reduction in most crops.
  4. 4. Environmental conditions that can cause stress Water-logging & drought Excessive soil salinity High or low temperatures Ozone Low oxygen Phytotoxic compounds Inadequate mineral in the soil Too much or too little light S S Jena
  5. 5. Characteristics of abiotic stresses  Unpredictable occurrence.  Some stresses are impossible to manage.  One stress may increase or decrease the level of another stress.  Differential response of plant sp. to a given stress  Effects generated by one abiotic stress may overlap with some effects of another stress.
  6. 6. PLANT RESPONSE TO STRESS Stresses trigger a wide range of plant responses:  Altered gene expression  Cellular metabolism  Changes in growth rates and crop yields S S Jena
  7. 7. Ozone Extreme temperature Flooding Drought Salt Physiological & developmental event Altered cellular metabolism PLANT RESPONSE TO STRESS S S Jena
  8. 8. Resistance or sensitivity of plants to stress depends on Environmental stress Stress characteristics Plant characteristics Response Result Severity Duration No. of exposures Continuation of stress Organ or tissue in question Stage of develop-ment Genotype Resistance Susceptibility Survival & growth Death S S Jena
  9. 9. Stress resistance mechanisms  Avoidance - prevents exposure to stress  Tolerance - permit the plant to withstand stress  Acclimation - alter their physiology in response to stress S S Jena
  10. 10. Stress resistance mechanisms Saguaro Honey mesquite Spinach Mohave desert star Black spruce Abiotic Stress Acclimation Resistance - Stress avoidance - Stress tolerance S S Jena
  11. 11.  Drought: I. DROUGHT STRESS Moisture scarcity which restricts the full expression of genetic yield potential of a plant.  Mechanisms of drought resistance: a) Drought escape: mature early b) Drought avoidance: Maintain water balance c) Drought tolerance: higher yield even under low water potential S S Jena
  12. 12. Effects of drought at cellular level  Structures of membrane and organelles  Structures of macromolecules like proteins and nucleic acids  Amounts of specific mRNA  Rate of translation  Pressure differential across the membrane-cell wall complex; in turn affects cell expansion.  A combination of the above. S S Jena
  13. 13. Morphological features providing drought resistance • Earliness • Reduced tillering • Leaf rolling, folding, shedding, leaf reflectance • Reduced leaf area; narrow leaf, change in leaf angle • Hairiness • Color of leaves • Wax coating • Root systems S S Jena
  14. 14. Physiological response to drought  Photosynthetic efficiency is reduced due to chloroplast damage  Reduced transpiration and reduced respiration losses  Stomatal behavior Biochemical response to drought  Accumulation of compatible solutes  Increase in ABA & Ethylene Protein synthesis Nitrate reductase activity S S Jena
  15. 15. Sources of drought resistance  Cultivated varieties  Land races  Wild relatives: e.g. Wheat: A.variabilis, A,speltoides, A.squarrosa Sugar cane: S. spontaneum  Transgenes : Rab (Responsive to abscisic acid) in rice S S Jena
  16. 16. Breeding methods and approaches Approaches:  Varieties adapted to a specific environment  Adaptation to variable environment  Combining drought resistance traits with high yield potential Breeding methods: Introduction  Selection  Hybridization  Mutation  Genetic engineering S S Jena
  17. 17. Osmotic adjustment  In response to dehydration or osmotic stress a series of compatible solutes/ osmolytes are accumulated for osmotic adjustment, water retention and free radical scavenging.  The cell actively accumulates solutes and as a result the solute potential (s) drops, promoting the flow of water into the cell. Few osmolytes:  Proline  Glycine betaine  Mannitol  Osmotin  D-Pinitol S S Jena
  18. 18. Stepwise gene expression in molecular responses to dehydration and low temperature S S Jena
  19. 19. Limitations  Generally resistant varieties have low yield; Do not have much adaptability.  Drought resistant genes may have linkage with undesirable genes.  Drought resistant traits may reduce yield.  Transfer of resistant genes from wild types may pose a problem  Creation of controlled moisture stress environment is a problem, selection require considerable resources S S Jena
  20. 20. Achievements  Rice: Akashi, Bala, IRS  Barley: Karan 280  Durum wheat: Gulab, Motia, Jay, Vijay  Ground nut: Jyothi, DH3-10  Sugarcane: Co 1148, Co 11158, Co 997  Maize: Early triumph, silver king  Potato: Rila, Viking S S Jena
  21. 21. II. SALT TOLERANCE Salt tolerance: Ability of plants to prevent ,reduce or overcome injurious effects of soluble salts present in their root zone Salinity can be overcome by 1) Soil reclamation: costly ,time consuming & short lived 2) Resistant varieties: less costly, more effective, long lasting but require longer period to develop. Characteristics of plants to salt :  Land races more tolerant than high yielding varieties  Salt tolerance capacity differs from species to species  Different plants show differential response to salinity S S Jena
  22. 22. Classification of plants based on salt tolerance 1. Highly tolerant crops: Sugar beet, barley, cotton, date palm, asparagus. 2. Moderately tolerant: Barley, rye, sorghum, wheat, safflower, Soya been 3. Moderately sensitive: Rice, corn, foxtail millet, cow pea, peanut, sugar cane, tomato, potato, radish, cabbage 4. Extremely sensitive: Citrus, strawberry, melon, peas, carrot, okra, onion. S S Jena
  23. 23. Symptoms of plant to salt stress Retardation of growth Necrosis Leaf abscission Loss of turgor Ultimate death of plant S S Jena
  24. 24. Mechanism of salt tolerance 1. Salt tolerance: By accumulating salt, generally in their cells or glands & roots. Halophytes show tolerance by ion accumulation mechanism 2. Salt avoidance: By maintaining their cell salt concentration unchanged either by water absorption (e.g. Rice, chenopodiaceae) or by salt exclusion (e.g. tomato, Soya bean, citrus, wheat grass) Glycophytes (nonhalophytes) owe their resistance primarily to avoidance e.g. barley S S Jena
  25. 25. S S Jena
  26. 26. Over-expression of AtNHX1 increases salt tolerance S S Jena
  27. 27. Breeding strategies  Breeding for yield potential should have greater emphasis than breeding for salt resistance.  Selection should be done in stresses target environments Screening techniques 1. Sand culture by using nutrient solution in sand & irrigation with saline water. 2. Solution culture by using solution culture tanks 3. Micro plot techniques by using small micro plots. S S Jena
  28. 28. Achievements Rice : Mohan, pokkali, SR23b, SR26b, CSR-2, CSR-3, CSR-6. Onion: Hissar-2, pb selection, Karchia, Karna-92. Okra: Pusa Sawani Barley: Ratna, RS-16, Karan-18, 19, 92 Sugar cane: Co7717, Co1148, Bo91 S S Jena
  29. 29. III. COLD TOLERANCE Chilling: When temp remain above freezing i.e. >0°C to < 10-15°C. Freezing: When temp remains below freezing i.e. <0°C. a) Chilling resistance Chilling sensitive plants are typically tropical plants. Temperate plants generally tolerate chilling injury.
  30. 30. Effects of chilling on plants  Reduced germination  Poor seedling establishment  Stunted growth  Wilting, Chlorosis, necrosis  Pollen sterility  Poor seed set/ seed formation.  Locked open stomata.  ABA accumulation At subcellular level:  Reduces membrane stability  Poor chlorophyll synthesis  Reduced photosynthesis  Toxicity due to H2O2 formation
  31. 31. Chilling tolerance mechanisms involve  Membrane lipid un-saturation  Reduced sensitivity of photosynthesis  Increased chlorophyll accumulation  Improved germination  Improved fruit/seed set  Pollen fertility Sources of chilling tolerance:  Late adopted breeding populations e.g. maize  Germ plasm  Induced mutants for cold tolerance  Cold tolerant somaclonal variants  Related wild species eg.tomato
  32. 32. b) Freezing resistance Dormant state is conducive to freezing resistance, while resistance is rare in actively growing tissue. As water in plants cool below 0°C, it may either 1) freeze i.e. form ice. 2) super cool with out forming ice.
  33. 33. Effects of freezing stress 1. Ice formation :  Intercellular ice formation:  Intracellular ice formation: it is most lethal may be due to physical disruption of sub cellular structure by ice crystals. 2. Membrane disruption: • Freezing causes disruption and alter the semi permeable properties of plasma membrane • Loss of solutes from the cells occur • Cells remain plasmolyzed even after thawing
  34. 34. 3. Super cooling:  In plants cooling of water below 0°C with out ice crystal formation is called super cooling  In plants water may cool down to -1 to -15°C  It is possible because internal ice-nucleators are absent.  This is regarded as imp mechanism of freezing avoidance.
  35. 35. Mechanism of freezing resistance 1. Freezing avoidance : The ability of plant tissues / or genes to avoid ice formation at sub zero temperature Super cooling is a mechanism of freezing avoidance which is controlled by  Lack of ice nucleators  Small cell size  Little or no intercellular space  Low moisture contents  Barriers against external nucleators
  36. 36. 2. Freezing tolerance: Ability of plants to survive the stress generated by extra cellular ice formation and to recover and re grow after thawing Components of freezing tolerance  Osmotic adjustment  Amount of bound water  Plasma membrane stability  Cell wall components properties  Cold responsive proteins, e.g. ABA
  37. 37. Genetic resources for freezing tolerance  Cultivated varieties  Germplasm lines  Induced mutations  Related wild species e.g. Wheat: Agropyron sp., Rye Oats: Avena sterilis  Transgenes: e.g. chemical synthesized anti freeze protein gene, ala3 in tobacco
  38. 38. Selection criteria: • Freezing test in laboratory • Cryo freezing • Osmoregulation • Field survival Problems in breeding for freezing tolerance: o Breeding work under field conditions is highly influenced by other environmental factors and biotic stresses o Due to large G x E interaction field survival shows poor heritability o Lab tests yet to be developed to screen large breeding populations
  39. 39. IV. OXIDATIVE STRESS  Results from conditions promoting the formation of active oxygen species that damage or kill cells Environmental factors that cause oxidative stress:  Air pollution (increased amounts of ozone or sulfur dioxide)  oxidant forming herbicides e.g. Paraquat dichloride  heavy metals  drought  heat and cold stress  wounding  UV light  Intense light that stimulate photoinhibition S S Jena
  40. 40. Reactive oxygen species (ROS)  Formed during certain redox reactions and during incomplete reduction of oxygen or oxidation of water by the mitochondrial or chloroplast electron transfer chain.  e.g. Singlet oxygen, hydrogen peroxide, superoxide anion, hydroxyl and perhydroxyl radicals The negative effects of ozone on plants  Decreased rates of photosynthesis  Leaf injury  Reduced growth of shoots and roots  Accelerated senescence  Reduced crop yield S S Jena
  41. 41. Ozone Damage  Alters ion transport  Increases membrane permeability  Inhibits H+-pump activity  Collapses membrane potential  Increases Ca2+ uptake from the apoplasm  Oxidative damage to biomolecules S S Jena
  42. 42. Resistance to ozone  Utilizes either avoidance or tolerance  Avoidance involves physically excluding the pollutant by closing the stomata, the principal site at which ozone enters the plant  Tolerance - biochemical responses that induce or activate the antioxidant defence system and possibly also various repair mechanisms Anti-oxidants: Over expression of certain enzymes such as superoxide dismutase, ascorbate peroxidase and glutathione reductase has been implicated in free radical detoxification and scavenging of free radicals under oxidative stress. S S Jena
  43. 43. Salicylic acid and ethylene • Ozone exposure results in increased amounts of H2O2, which stimulate the production of SA • Results in a transient increase in the number of transcripts that encode defence-related secondary metabolites e.g. phytoalexins, cellular barrier molecules e.g. lignins, callose, and extensins, PR proteins e.g. (13) -glucanase, chitinase, gluthatione S-transferase and phenylalanine ammonia lyase • Increases ethylene production by inducing increases in ACC synthase and ACC oxidase gene transcription S S Jena
  44. 44. S. S. Jena
  45. 45. QUERIES…. S S Jena
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