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Plant stresses and responses

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De Block et al., Plant J. 41:95 (2005) Plant stresses and responses Plant Physiol Biotechnol 3470 March 21, 2006 Chp 21 Plants are sessile and must deal with stresses ... – PowerPoint PPT presentation

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Title: Plant stresses and responses


1
Plant stresses and responses
De Block et al., Plant J. 4195 (2005)
  • Plant Physiol Biotechnol 3470
  • March 21, 2006
  • Chp 21

2
Plants are sessile and must deal with stresses in
place
  • Plants cannot avoid stress after germination
  • How plants deal with stress has implications in
  • Ecology Stress responses help explain geographic
    distribution of species
  • Crop science Stress affects productivity
  • Physiology and biochemistry Stress affects the
    metabolism of plants and results in changes in
    gene expression

www.grainscanada.gc.ca
  • From engineering, stresses cause strains
    (responses of stressed objects) changes in gene
    expression and metabolism in plants
  • Biological stress difficult to define/quantify
  • What is normal metabolism?
  • Limitations to yield?
  • Where on gradient of availability of limiting
    resource does stress begin?
  • Varies by species, ecotype

Heat-stressed wheat
3
Stresses are abiotic or biotic
Fig. 21.1
  • ABIOTIC STRESSES
  • Environmental, non-biological
  • Temperature (high / low)
  • Water (high / low)
  • Salt
  • Radiation
  • Chemical
  • BIOTIC STRESSES
  • Caused by living organisms
  • Fungi
  • Bacteria
  • Insects
  • Herbivores
  • Other plants/competition
  • Stresses cause responses in metabolism and
    development
  • Injuries occur in susceptible plants, can lead to
    impeding flowering, death
  • Ephemeral plants avoid stress
  • Mexican poppies in US desert SW
  • Only bloom after wet winter
  • Die before summer returns

Preferable!
http//www.geo.arizona.edu/gallery/US/tuc_2.html
4
Plants must be stress resistant to survive
  • Avoidance also possible by morphological
    adaptations
  • Deep tap roots in alfalfa allow growth in arid
    conditions
  • Desert CAM plants store H2O in fleshy
    photosynthetic stems
  • Stress resistant plants can tolerate a particular
    stress
  • Resurrection plants (ferns) can tolerate
    dessication of protoplasm to lt7 H2O ? can
    rehydrate dried leaves
  • Plants may become stress tolerant through

Alfalfa plant
  • Adaptation heritable modifications to increase
    fitness
  • CAM plants morphological and physiological
    adaptations to low H2O environment
  • Acclimation nonheritable physiological and
    biochemical gene expression
  • Cold hardening induced by gradual exposure to
    chilling temps, a/k/a cold-hardy plants

Alfalfa taproot
www.agry.purdue.edu www.omafra.gov.on.ca
Heat stressed rose leaf
5
Lets walk through one each of important abiotic
and biotic stresses
  • View how they affect metabolism
  • Determine how the plant responds to counter the
    stress
  • ABIOTIC STRESS Temperature
  • Plants exhibit a wide range of Topt (optimum
    temperature) for growth
  • We know this is because their enzymes have
    evolved for optimum activity at a particular T
  • Properly acclimated plants can survive
    overwintering at extremely low Ts
  • Environmental conditions frequently oscillate
    outside ideal T range
  • Deserts and high altitudes hot days, cold nights
  • Three types of temperature stress affect plant
    growth
  • Chilling, freezing, heat

Topt
Growth rate
Growth temperature
6
Suboptimal growth Ts result in suboptimal plant
development
  • Chilling injury
  • Common in plants native to warm habitats
  • Peas, beans, maize, Solanaceae
  • Affects
  • seedling growth and reproduction
  • multiple metabolic pathways and physiological
    processes
  • Cytoplasmic streaming
  • Reduced respiration, photosynthesis, protein
    synthesis
  • Patterns of protein expression

Transition temperature
Membrane fluidity affects permeability!
http//cropsoil.psu.edu/Courses/AGRO518/CHILLING.h
tm
  • Initial metabolic change precipitating metabolic
    shifts thought to be alteration of physical state
    of cellular membranes
  • Temperature changes lipid and thus membrane
    properties
  • Chilling sensitive plants have more saturated FAs
    in membranes these congeal at low temperature
    (like butter!)
  • Liquid crystalline ? gel transition occurs
    abruptly at transition temperature

7
Biotic stresses are mitigated by plants
elaborate defense strategies
Buchanan et al., Biochemistry molecular
biology of plants, 2001
Defenseless
Wild type
  • BIOTIC STRESS Pathogen (e.g., fungus) invasion
  • Plant reaction to invading pathogens center
    around the hypersensitive reaction
  • The hypersensitive reaction initiates many
    changes in plant physiology and biochemistry
  • Early activation of defense related genes to
    synthesize pathogenesis related (PR) proteins
  • Protease inhibitors to stop cell wall lysis by
    specific enzymes expressed by pathogen
  • Bacterial cell wall lytic enzymes (chitinase,
    glucanase)
  • Change cell wall composition
  • Express enzymes providing structual support to
    cell walls via synthesis of lignin, suberin,
    callose, glycoproteins
  • Synthesize secondary metabolites to isolate and
    limit the pathogen spread
  • These include isoflavonoids, phytoalexins
  • Apoptosis at invasion site to physically cut off
    rest of plant
  • Sequential or parallel events??

8
How does the plant recognize and defend itself
against pathogens?
  • Plant disease has an underlying genetic basis
  • Pathogens may be more or less potentially
    infectious to a host
  • virulent on susceptible hosts
  • avirulent on non-susceptible hosts
  • Pathogens carry avirulence (avr) genes and hosts
    carry resistance (R) genes
  • The normal presence of both prevents pathogens
    from attacking the plant
  • Infection occurs when pathogen lacks avr genes or
    plant is homozygous recessive for resistance
    genes (rr)
  • In these cases, the plant cannot initiate the
    hypersensitive reaction
  • This is bad news!
  • The plant requires this response to survive!
  • Note the communication between pathogen and plant
  • Pathogen avr genes may code for proteins that
    produce elicitors
  • bits of pathogen polysaccharides, chitin, or
    bits of damaged plant cell wall polysaccharides
  • Plant R genes may be elicitor receptors

9
The hypersensitive reaction initiates a plant
immune response
  • The long term plant resistance to a pathogen is
    similar to a mammalian immune response
  • This is known as systemic acquired resistance
    (SAR)
  • Secondary metabolites induced by the
    hypersensitive reaction initiate changes in
    metabolism in other plant organs through control
    of signal transduction chains
  • Hours to days capacity to resist pathogens
    spreads throughout plant
  • Immune capacity SAR
  • SAR signaling involves salicylic acid (SA), a
    natural secondary metabolite
  • SA both induces pathogenesis related gene
    expression and enhances resistance to infection
    by plant viruses

Fig 21.17
10
Salicylic acid induces systemic acquired
resistance
Fig 21.18
volatilized
  • Local SA production induces distal production and
    SAR via
  • SA transport in xylem
  • Methylation into MSA, volatilization and distal
    detection
  • High constitutive SA levels result in plants with
    high ability to withstand pathogens
  • Mechanism by which SA induces SAR unknown
  • Jasmonic acid also mediates disease and insect
    resistance
  • JA also mediates other developmental responses
    PGR?
  • All stress affects photosynthesis productivity
    and survival
  • Knowledge of how stress is perceived and
    transduced central to understanding plant
    metabolism
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