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- plant responses to environmental stress (physiological, biochemical, genetic)

- research approaches for study of environmental stresses.

- biochemical, genetic and molecular on one hand mechanisms responsible for

environmental stress tolerance on the other hand the factors causing injury

during stress.

- integrate concepts from related disciplines

COURSE OBJECTIVES: to gain knowledge about

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Plant response to environmental stimuli

involves perception, transduction, adaptation Sensing changes in the surrounding environment

Responding to gravity and direction of light, etc.

Adjusting their growth pattern and development

Control systems in plants involve

adaptations, adaptations, adaptations

Environmental stimuli that affect plant growth

Plants need to monitor everything in order to optimize growth (i.e. to adapt) to environmental conditions, endogenous present & future

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Plants have to exploit their immediate environment to maximum effect. Their inability to move means that the best way of dealing with stress is by physiological or morphological changes.

Abiotic stresses, and ways to adapt to them are numerous and interlinked

there’s more than one way to skin a cat

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In biology, stress is the driving force behind the process of adaptation

and evolution

AbioticWaterOxygenNutrientsTemperatureSalt stressPollutants excess or

deficitBioticInsectsWeedsPathogensPlant

competition

mutations

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Resistance to drought and salt stresses is interlinked

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Example of elucidating stress responses

Inputs for ionic and osmotic signaling pathways are ionic (excess Na+) and osmotic (turgor) changes. The output of ionic and osmotic signaling is cellular and plant homeostasis. Annual Review of Plant Biology 53: 247

SIGNAL TRANSDUCTION

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Na+

K+

H+

Na+

Na+

H+

H+

H+ATP

PPi

H+ATP

Tonoplast

Vacuole

Plasma Membrane

V-ATPase

P-ATPase

V-PPase

Na+/H+ antiport

K+/Na+ ratio

K+/Na+ selectiveVICs

K+

High-affinity K+ transporters

Adapted from Mansour et al. 2003

Na+ UPTAKE/EXTRUSION IN THE PLANT CELL

Na+

Na+

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The Four Elements of Abiotic Stress

STRESSSTRESS

WaterWater

LightLight

NutrientsNutrients

TemperatureTemperature

time

stre

ss

in general, performance below optimal genetic potential is

indicative of stress

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Plant Responses to Stress

Mechanical concept of stressStress is a force per unit areaStrain is a change in dimension in response to

stress (in other words, deformation of a physical body under the action of applied forces)

Failure of a material occurs when the

material cannot strain sufficiently to resist stress

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Plant Responses to Stress

Biological concept of stress Abiotic (physical or chemical) or biotic factor adversely affecting an organism Measured as effect on growth rate and

productivity

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A comparison of the record yields and the average yields indicates that mostly crops are only reaching 20% of their genetic potential due to biotic categories: disease, insect and weeds. The major reduction in yield (~ 70%) is due to abiotic stress. The most significant abiotic stress is water stress, both deficit stress (drought) and excess stress (flooding, anoxia).

  average losses

 Crop recor

d yield*

 average

yield*

 disease

 insect  weed other

(abiotic)

 corn 19,30

0 4,600  750  691  511  12,700

 wheat 14,50

0 1,880  336  134  256  11,900

 soybean

 7,390  1,610  269  67  330  5,120

 sorghum

 20,000

 2,830  314  314  423  16,200

 oats 10,60

0 1,720  465  107  352  7,960

 barley 11,40

0 2,050  377  108  280  8,590

 potatoes

 94,100

 28,300

 8,000  5,900  875  50,900

 sugar beets

 121,000

 42,600

 6,700  6,700  3,700  61,300

% of record yield

 21.6%  4.1%  2.6%  2.6%  69.1%

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Factors that determine plant stress responses

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Strategies of stress tolerance in plantsStrategies of stress tolerance in plants

constitutive succulent constitutive deep roots

Drought avoidance

induced freezingtoleranceresistance

If plants can induce stress resisting genes Why these genes are not constitutively on?

Susceptibility -slowed growth--senescence--death Avoidance -deep rooting -short life cycle -leaf modifications Resistance -ex. can survive desiccation of

protoplasm “resurrection plants”

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I. Important concepts of stress I. Important concepts of stress physiologyphysiology

• Stress– external factor that is disadvantageous to plants; survival, growth, development, yield

• Acclimated (Hardened)- increased stress tolerance as a result of prior exposure to a stress condition

• Cross Resistance- tolerance to a stress based on exposure to a previous stress event of a different nature

• Adaptation- is a genetically determined level of resistance acquired by a process of selection over many generations

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Plants respond to stress on a cellular and on the whole plant levels

growth regulation by BON1 is mediated through defense responses. BON1 is a negative regulator of a Resistance (R) gene SNC1. The bon1-1 loss-of-function mutation activates SNC1, leading to constitutive defense responses and, consequently, reduced cell growth

link between biotic and abiotic stress signal transduction and plant development

bon1 are miniature at 22oC but like wild-type at

28oC

Responses to Biotic and Abiotic stresses are connected genetically:

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• Plants adapt to changing environmental conditions through changes in expression patterns of numerous genes.

Plant Response to Stress

• There is a group of genes whose expression confers resistance to a given stress.

• There is a common core of defense genes, which responds to several different stresses (general stress-response genes) versus stress-specific genes.

• Increase in expression of protective genes is co-regulated

and is correlated with resistance to oxidative stress.

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Methods to study stress resistance

1. Biochemical Approach– control vs. resistant plants

– control vs. induced conditions

2. The Genetic Approach– identify mutants with altered response

– suppressor mutations

3. Comparative approach: complementation in yeast

4. The Genomic Approach

5. The Metabolomic Approach

6. The Ionomic Approach

7. Discovery vs. Hypothesis-Driven Science

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II. PLANT RESPONSES TO HORMONES

Hormone = A compound produced by one part of an organism that is transported to other parts where it triggers a response in target cells and tissues.

B. Plant hormones help coordinate growth, development, and responses to environmental stimuli

1) By affecting division, elongation, and differentiation of cells 2) Effects depend on site of action, stage of plant growth and hormone

concentration 3) The hormone signal is amplified, perhaps by affecting gene

expression, enzyme activity, or membrane properties 4) Reaction to hormones depends on hormonal balance 5) Five classes of plant hormones:

(1) Auxin (such as IAA).(2) Cytokinins (such as zeatin) (3) Gibberellins (such as GA3)(4) Abscisic acid (5) Ethylene

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• hormones are chemical signals that are produced in one part of the body, transported to other parts, bind to specific receptors, and trigger responses in targets cells and tissues.– Only minute quantities of hormones are necessary to induce substantial

change in an organism.

– Often the response of a plant is governed by the interaction of two or more hormones.

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Plant hormones are produced at low concentration– Signal transduction pathways amplify the hormonal signal many fold and

connect it to a cell’s specific responses.

– These include altering the expression of genes, by affecting the activity of existing enzymes, or changing the properties of membranes.

– Response to a hormone usually depends not so much on its absolute concentration as on its relative concentration compared to other hormones

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Stress physiology...Stress physiology...

Biological membranes are the primary target of many environmental stresses. Membranes are made of phospholipids and proteins.

Biological membranes are the primary target of many environmental stresses. Membranes are made of phospholipids and proteins.

phospholipidphospholipid

phospholipidphospholipid

hydrophilic exterior

hydrophilic exterior

hydrophobic interior

hydrophobic interior

~50:50 ,% thus not just a barrier