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

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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 theres more
than one way to skin a cat
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Abiotic Water Oxygen Nutrients Temperature Salt
stress Pollutants excess or deficit Biotic Insec
ts Weeds Pathogens Plant competition
mutations
In biology, stress is the driving force behind
the process of adaptation and evolution
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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
Na
Na
H
PPi
K
H
High-affinity K transporters
V-PPase
H
Na
Na/H antiport
Vacuole
Na
Na
Tonoplast
V-ATPase
K
K/Na selectiveVICs
H
ATP
ATP
K/Na ratio
H
P-ATPase
Adapted from Mansour et al. 2003
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The Four Elements of Abiotic Stress
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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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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(No Transcript)
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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
Drought avoidance
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• 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
Responses to Biotic and Abiotic stresses are
connected genetically
bon1 are miniature at 22oC but like wild-type at
28oC
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
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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

• Biochemical Approach
• control vs. resistant plants
• control vs. induced conditions
• The Genetic Approach
• 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

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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 cells
  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.
5050 , thus not just a barrier
phospholipid
hydrophobic interior
phospholipid
hydrophilic exterior