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CHAPTER 22

CHAPTER 22. Responses to Abiotic Stresses. Introduction 22.1 Plant responses to abiotic stresses 22.2 Stresses involving water deficit 22.3 Osmotic adjustment and its role in tolerance to drought and salinity 22.4 Impact of water deficit and salinity on transport across plant membranes

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CHAPTER 22

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  1. CHAPTER 22 Responses to Abiotic Stresses

  2. Introduction 22.1 Plant responses to abiotic stresses 22.2 Stresses involving water deficit 22.3 Osmotic adjustment and its role in tolerance to drought and salinity 22.4 Impact of water deficit and salinity on transport across plant membranes 22.5 Additional genes induced by water stress 22.6 Freezing stress 22.7 Flooding and oxygen deficit 22.8 Oxidative stress 22.9 Heat stress

  3. STRESS? • Biotic stress (chapter 21) • Abiotic Stress (chapter 22) What is Abiotic Stress? Environmental condition that cause damage are water logging, drought, high or low terperatures, excessive soil salinity, inadequate mineral nutrients in the soil, and too much or too little light… What is the effect of stress in plant? Stresses trigger a wide range of plant responses - gene expression and cellular metabolism to change in growth rate and crop yields. Some responses enable a plant to acclimate to the stress Identifying which responses promote or maintain plant growth and development during stress is important for understanding the stress response process.

  4. 22.1 Plant responses to abiotic stresses 22.1.1 Plant stresses greatly diminish crop yields Abiotic and biotic stress reduce average productivity of crop by 65% to 87% + Biotechnology Classical breeding technique Stress tolerance crop plant = enhance food Many factors determine how plants respond to environmental stress

  5. 22.1.2 Resistance mechanisms allow organisms to avoid or tolerate stress Photosynthetic stem Deep root Osmotic tolerance Wet season life cycle Cold hardy tree Stress resistance mechanism -- Avoidance & Tolerance -- Acclimation

  6. 22.1.3 Gene expression patterns often change in response to stress

  7. 22.2 Stresses involving water deficit 22.2.2 Water potential and relative water content describe the water status of plant. Equation 22.1: Water potential Ψw = Ψs + Ψp + Ψg + Ψm Equation 22.2: Water potential (simplified) Ψw = Ψs + Ψp Ψw = water potential Ψs = solute potential Ψp = pressure potential Ψg = gravitational potential Ψm = matric potential

  8. 22.3 Osmotic adjustment and its role in tolerance to drought and salinity 22.3.1 Osmotic adjustment is a biochemical mechanism that helps plant acclimate to dry or saline soil. • Osmotic adjustment • ; cell actively accumulates solutes • and, as ad result, Ψs drops, promoting • the flow of water into the cell

  9. 22.3.2 Compatible solutes share specific biochemical attributes. Sugar (sucrose, fructose) Sugar alcohol (glycerol, methylated inositol) Complex sugar (trehalose, raffinose, fructan) Charged metabolite (glycine betaine, DMSP, proline, ectoine) Dae-Jin Yun, 2005

  10. H2O The hydration shells of macromolecules are not disrupted by compatible solutes

  11. Osmotic adjustment in a mesophyll cell of a salt stressed spinach leaf.

  12. 22.3.3. Some compatible solutes may serve protective functions Glycine betaine prevents salt induced inactivation of Rubisco and destabilization of the oxygen-evolving complex of Photosystem Ⅱ. Sorbitol, mannitol, myo-inositol and proline can reduce hydroxyl radicals in vitro. 22.3.4. Transgenic plants can be used to test the acclimative functions of specific osmolytes. osmoprotectant encoding gene

  13. 22.3.5. Glycine betaine accumulation is regulated by the rates of its synthesis and transport

  14. 22.3.6. In some plant species, salt stress inhibits sucrose synthesis and promotes accumulation of mannitol • Salt stress inhibit sucrose synthesis • Salt stress also down-regulates NAD+ dependent mannitol dehydrogenase. • Transgenic plants expressing NAD+ dependent mannitol-1-phosphate • dehydrogenase(fructose 6-phosphate  mannitol 1-phosphate) accumulate • mannitol. • - Mannitol accumulating transgenic seed was able to germinate in the salt media.

  15. 22.3.7. Taxonomically diverse plants accumulate pinitol in response to salt stress. • D-Pinitol • a cyclic sugar alcohol (major solute in the Pinaceae) • accumulate in salt tolerant legumes • Pinitol can contribute 70% of the soluble carbohydrate • in salt treated plant. • In leaf, pinitol localized to the chloroplast and cytosol • Increase in the concentration of pinitol in salt exposed plant, • myo-inositol 6-O-methyltransferase induced by 60-fold

  16. 22.4Impact of water deficit and salinity on transport across plant membranes

  17. 22.4.1 Carriers, pumps, and channels operate to minimize the impact of perturbing ions on cell metabolism. • by the active transport of cytosolic Na+ across the plasma membrane out of cells • - Na+/H+ antiporter in PM • - energized by H+-ATPases • by the active transport of cytosolic Na+ across the tonoplast membrane into vacuole • - Na+/H+ antiporter in Vacuole • - energized by H+-ATPases

  18. Chemiosmotic processes in plant cell Energize Na+/H+ antiports • Plassma membrane H+-ATPase • Vacuolar H+-ATPase • Tonoplast membrane H+-pyro phosphatase

  19. 22.4.2 Synthesis and activity of aquaporin may be up-regulated in response to drought aquaporin • Water channels • Facilitate water movement in drought stress tissues and promote the rapid recovery of turgor on watering • Rd28 gene encodes a member of the MIP family

  20. Expression of MIP-related genes watering drought Increase or decreases of Rd28 gene

  21. heat 22.5Aditional genes induced by water stress drought Oxyzen species Water stress salinity pathogens Multiple stress-related roles

  22. 22.5.1 some seed proteins may protect vegetation tissues from stress. Lea genes • Seeds during maturation and desiccation • Vegetative tissues of plants exposed to stresses • Cytoplasmic location • Rich in alanine and glycine and lacking cysteine and tryptophan

  23. Five group of LEA proteins

  24. 22.5.2 osmotin, a tobacco protein with antifungal activity, accumulates during water deficit. Induction of osmotin protein Induction of osmotin gene • Cold • Ethylene • Water deficit • UV-light • Lack of water • Salinity • Fungal infection • Fungal infection • Wounding • Ethylene • Auxin • ABA • Salinity • TMV Infection

  25. Model for antifungal action of osmotin Fungal hypha releases fungal toxins 1 Disrupt the plant membrane 2 Causing it to leak nutrients that the fungus utilizes 3 4 The plant cell loses turgore Promotes the acumulation of osmotin 5 Osmotin from the leacking cell comes into contact with a fungal membrane receptor 6 Facilitates the formation of pores in the fungal membrane 7 Limit the effect of osmotin 8

  26. 22.5.3 some genes induced by water stress are responsive to ABA. ABA induced gene • Increased in response to water deficit and low temperature • Stomatal closure • ABI1 and ABI2 gene are thought to encode protein phosphatases • Regulating tyrosin kinase

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