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