Transcript COURSE OBJECTIVES

COURSE OBJECTIVES: to gain knowledge about
- 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
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Environmental stimuli that affect
plant growth
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
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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Abiotic
Water
Oxygen
Nutrients
Temperature
Salt stress
Pollutants
excess or
deficit
Biotic
Insects
Weeds
Pathogens
Plant competition
mutations
stress is the driving force behind
the process of adaptation and evolution
In biology,
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Resistance to drought and salt stresses is interlinked
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Example of elucidating stress responses
SIGNAL TRANSDUCTION
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
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Na+ UPTAKE/EXTRUSION IN THE PLANT CELL
Plasma Membrane
PPi
Na+
K+
Na+
H+
H+
High-affinity K+
transporters
V-PPase
H+
Na+
Na+/H+ antiport
Vacuole
Na+
Na+
K+
Tonoplast
V-ATPase
K+/Na+ selectiveVICs
H+ ATP
K+/Na+ ratio
H+
ATP
P-ATPase
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Adapted from Mansour et al. 2003
The Four Elements of Abiotic Stress
stress
Water
STRESS
Temperature
Light
time
Nutrients
in general, performance below optimal
genetic potential is indicative of stress
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Plant Responses to Stress
Mechanical concept of stress
Stress is a force per unit area
Strain 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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average losses
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).
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Crop
record
yield*
average
yield*
disease
insect
weed
other
(abiotic)
corn
19,300
4,600
750
691
511
12,700
wheat
14,500
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
10,600
1,720
465
107
352
7,960
barley
11,400
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
21.6%
4.1%
2.6%
2.6%
69.1%
% of
record
yield
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Factors that determine plant stress responses
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Strategies of stress tolerance in plants



Susceptibility
-slowed growth--senescence--death
Avoidance
-deep rooting
-short life cycle
-leaf modifications
Resistance
-ex. can survive desiccation of protoplasm
“resurrection plants”
constitutive deep roots
constitutive succulent
If plants can induce
stress resisting genes 
Why these genes are not
constitutively on?
induced freezing
toleranceresistance
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Drought avoidance
I. Important concepts of stress physiology
• 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
link between biotic and abiotic stress
signal transduction and
plant development
bon1 are miniature at 22oC
but like wild-type at
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28oC
Responses to Biotic and Abiotic stresses are
connected genetically:
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
Plant Response to Stress
• Plants adapt to changing environmental
conditions through changes in expression
patterns of numerous genes.
• 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
–
–
2.
The Genetic Approach
–
–
3.
4.
5.
6.
7.
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control vs. resistant plants
control vs. induced conditions
identify mutants with altered response
suppressor mutations
Comparative approach: complementation in yeast
The Genomic Approach
The Metabolomic Approach
The Ionomic Approach
Discovery vs. Hypothesis-Driven Science
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...
Biological membranes are the primary target of many
environmental stresses. Membranes are made of
phospholipids and proteins.
~50:50 %, thus not just a barrier
phospholipid
hydrophobic
interior
phospholipid
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hydrophilic
exterior