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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
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
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 toomuch or too little light…
STRESS?
Biotic stress (chapter 21)
Abiotic Stress (chapter 22)
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 anddevelopment during stress is important for understanding
the stress response process.
22.1 Plant responses to abiotic stresses
22.1.1 Plant stresses greatly diminish crop yields
Many factors determine how plants respond to environmental stress
Abiotic and biotic stress reduce average productivity of crop by 65% to 87%
BiotechnologyClassical breeding
technique+ Stress tolerance crop plant= enhance food
22.1.2 Resistance mechanisms allow organisms to avoid or tolerate stress
Stress resistance mechanism -- Avoidance & Tolerance -- Acclimation
Deep rootPhotosynthetic stem
Wet season life cycle
Osmotic tolerance
Cold hardy tree
22.1.3 Gene expression patterns often change in response to stress
22.2.2 Water potential and relative water content describe the water status of plant.
22.2 Stresses involving water deficit
Equation 22.1: Water potential
Ψw = Ψs + Ψp + Ψg + Ψm
Equation 22.2: Water potential (simplified)
Ψw = Ψs + Ψp
Ψw = water potentialΨs = solute potentialΨp = pressure potentialΨg = gravitational potentialΨm = matric potential
22.3.1 Osmotic adjustment is a biochemical mechanism that helps plant acclimate to dry or saline soil.
22.3 Osmotic adjustment and its role in tolerance to drought and salinity
• Osmotic adjustment; cell actively accumulates solutesand, as ad result, Ψs drops, promotingthe flow of water into the cell
22.3.2 Compatible solutes share specific biochemical attributes.
Dae-Jin Yun, 2005
Sugar (sucrose, fructose)Sugar alcohol (glycerol, methylated inositol)Complex sugar (trehalose, raffinose, fructan)Charged metabolite (glycine betaine, DMSP, proline, ectoine)
The hydration shells of macromolecules are not disrupted by compatible solutes
H2O
Osmotic adjustment in a mesophyll cell of a salt stressed spinach leaf.
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 .ⅡSorbitol, 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
22.3.5. Glycine betaine accumulation is regulated by the rates of its synthesis and transport
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.
22.3.7. Taxonomically diverse plants accumulate pinitol in response to salt stress.
D-Pinitol1. a cyclic sugar alcohol (major solute in the Pinaceae)2. accumulate in salt tolerant legumes3. Pinitol can contribute 70% of the soluble carbohydrate in salt treated plant.4. In leaf, pinitol localized to the chloroplast and cytosol5. Increase in the concentration of pinitol in salt exposed plant, myo-inositol 6-O-methyltransferase induced by 60-fold
22.4 Impact of water deficit and salinity on transport across plant membranes
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
Chemiosmotic processes in plant cell
Energize Na+/H+ antiports
Plassma membrane H+-ATPase
Vacuolar H+-ATPase
Tonoplast membrane H+-pyro phosphatase
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
Expression of MIP-related genes
Increase or decreases of Rd28 gene
drought watering
22.5 Aditional genes induced by water stress
heat
drought
salinity
Oxyzen species
pathogens
Multiple stress-related roles
Waterstress
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
Five group of LEA proteins
22.5.2 osmotin, a tobacco protein with antifungal activity, accumulates during water deficit.
Induction of osmotin protein
ABA
Ethylene
Auxin
TMV Infection Salinity
Lack of water
Cold
UV-light
WoundingFungal infection
Ethylene
Fungal infection
Salinity
Water deficit
Induction of osmotin gene
Model for antifungal action of osmotin
1
2
3
4
5
6
7
8
Disrupt the plant membrane
Causing it to leak nutrients that the fungus utilizes
The plant cell loses turgore
Promotes the acumulation of osmotin
Osmotin from the leacking cell comes into contact with a fungal membrane receptor
Fungal hypha releases fungal toxins
Facilitates the formation of pores in the fungal membrane
Limit the effect of osmotin
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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