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B3.0 > Plant Stress Responses > Flashcards

Plant Stress Responses Flashcards

1
Q

Stress

A
  • suboptimal environmental condition that adversely affects plant growth & development
  • normal part of life; varies in diversity and severity
  • reduces yields >50% (potential maximum vs yield losses)
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2
Q

Abiotic:

A
  • water: drought, flooding
  • temperature: heat, chilling, freezing
  • light: high, shading, UV
  • nutrient: deficiency, excess (micro and macro)
  • salinity
  • heavy metal toxicity + xenobiotics: pesticides, herbicides, air pollutants
  • mechanical: touch, gravity, pressure, wounding
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3
Q

Biotic:

A
  • pathogens: viruses, viroids, bacteria, fungi, oomycetes, nematodes, phytopalms
  • pests: herbivores, insects, mites etc.
  • plants: parasites, interspecific (weeds), intraspecific
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4
Q

Acclimation

A
  • individual level
  • caused by local stress acting on genetically determined physiological responses
  • non-heritable (except epigenetics)
  • elastic (reversible)
  • timescale: short term (mins-> hours), long term (days-> months)
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5
Q

Adaptation

A
  • population level
  • stress-driven natural selection acting on allelic variation
  • heritable
  • plastic (irreversible)
  • multiple generations (evolutionary)
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6
Q

Stress response:

A

1) time of exposure
2) intensity
3) plant genotype
4) physiological condition
5) developmental stage/organ

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7
Q

Types of stress response curves

A
  • essential + non-essential environmental factors
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8
Q

Essential environmental factors

A
  • optimal range
  • sub- (deficiency), supra- (excess)
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9
Q

Non-essential environmental factors

A
  • immediate adverse effect (e.g. some Biotic stresses, wounding)
  • tolerance (low intensity; e.g. some biotic stress, salinity, xenobiotics)
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10
Q

Strategies of stress responses

A

Susceptibility -> resistance;
- tolerance: endure
- avoidance; reduce exposure
- both lead to survival
- if unable to recognise/respond: death

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11
Q

Drought tolerance

A

Selaginella lepidophylla “resurrection plants” lose 90% cellular water

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12
Q

Freezing tolerance

A

Antifreeze protein accumulation to control ice crystal growth

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13
Q

Freezing tolerance

A

Antifreeze protein accumulation to control ice crystal growth

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14
Q

Drought avoidance

A
  • Ursinia in Namaqualand, S. Africa
  • germination in wet season/after rainfall
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15
Q

Freezing avoidance

A

Senecio keniodendron (giant groundsel) folds leaves to insulate meristem

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16
Q

Phases of stress acclimation

A
  1. Homeostasis = no stress
  2. Alarm
  3. Acclimation/ acute damage
  4. Maintenance / exhaustion
  5. Recovery / system failure
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17
Q

Stress priming

A
  • short and long term memory
  • trans-generational under debate
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18
Q

Stress priming depends on

A

1) physical marks on chromatin (DNA methylation, histone modifications)
2) diffusible signal conc (hormone, TFs)
- avoids costs associated w constitutive gene expression

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19
Q

Memory genes

A

Higher expression during stress

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20
Q

Stress responses can

A
  • involve extra/intracellular single d
  • be specific/general
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21
Q

Process of stress response

A

1) immediate (e.g. stomata closure)
2) gene expression, metabolism
3) physiology
4) growth, development
5) acclimation

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22
Q

General responses

A
  • common signals to different stresses
  • ROS, low energy, Ca2+
  • MAPKs, energy-sensing SnRK1-TOR, Ca2+-dependent kinases
23
Q

General protection

A
  • tissue repair + removal of damaged components
  • removal/compartmentalisation of unnecessary factors
  • ROS detoxification
  • resource redistribution
24
Q

Specific responses

A
  • to particular stress types
  • signals + components
25
Q

Specific protection

A

E.g.
- antifreeze accumulation
- heavy metal compartmentalisation
- defence compounds

26
Q

ROS

A
  • damage proteins, lipids, DNA and cellular dysfunction
  • e.g. prevent stomata closure during drought
  • produced in several cellular compartments
  • dedicated enzyme systems to neutralise
  • “intentionally” produced in the apoplast
27
Q

ROS production

A
  1. < CO2
  2. < C assimilation rates
  3. < NADPH recycling
  4. No NADP for e’s
  5. E’s + excited chlorophyll react w O2
28
Q

Enzymatic antioxidants

A
  1. SOD
  2. APX (ascorbate peroxidase)
  3. GPX (guaiacol peroxidase)
  4. GST (glutathione-S-transferase)
  5. CAT
29
Q

Apoplast

A
  • stress triggers ^ in chronic Ca2+
  • different stresses activate different channels: Calcium signatures; amplitude, oscillations, duration
    • Ca2+ in external envrt
30
Q

Ca2+ signals

A
  • calmodulin (CaM)
  • CaM-like proteins (CMLs)
  • Ca2+-dependent protein kinases (CDPKs)
  • calcineurin B-like proteins (CBLs) + associated CIPK kinases
31
Q

Ca2+ signals affect

A
  • metabolism
  • transcription
  • transport
  • et al
32
Q

Long-distance signalling via ROS/Ca2+ waves:

A
  • signals propagate from stressed cells -> entire plant within ss, mins
  • via: plasmodesmata, apoplast, vasculature
33
Q

Stress signals

A
  • ROS/Ca2+ waves
  • electric currents
  • hydraulic signals
  • pH
  • eATP
  • phytohormones
  • hormone-like peptides
  • miRNAs
34
Q

Systemic ROS/Ca2+ wave propagation and

A

1) ROS-induced calcium release (RICR)
2) Calcium-induced calcium release (CICR)

35
Q

RICR

A
  • apoplastic ROS activate PM calcium channels
  • ^ cytosolic Ca2+ conc
  • Ca2+ -> plasmodesmata
36
Q

CICR

A
  • membrane component activation (extracellular ROS production)
  • initiates same cascades
  • neighbouring cell communication; self-propagating
37
Q

ROS/Ca2+ waves

A
  • alert cells to impending stress
  • triggered by different abiotic stresses/ pathogen infection / wounding
  • local signal -> whole plant
  • co-signals convey specificity
38
Q

ROS/Ca2+ Co-signals

A
  • pH
  • membrane potential
  • metabolites
  • hormones
  • eATP
39
Q

Systemic ROS

A

2’-7’-dichlorodihydrofluorescin diacetate

40
Q

Ca2+

A

Flourescence

41
Q

Different stresses lower energy production

A
  • shading, pollution, drought, salinity, heat, cold, flooding
  • SnRK1: crucial for stress tolerance
42
Q

SnRK1, SNF1, AMPK

A
  • ^ energy production (catabolism, Autophagy)
  • < energy consumption (anabolism, translation/growth)
43
Q

Low sucrose sugar status (stress!)

A
  • SnRK1 inhibits TOR kinase (growth agonist)
44
Q

High sucrose sugar status (optimal)

A
  • sucrose inhibits SnRK1
45
Q

Plants have to balance

A
  • growth (anabolism, developmental progression)
  • survival (catabolism, nutrient mobilisation, stress responses)
46
Q

Tradeoff:

A

^SR = <G

47
Q

Energy sensing pathways

A

1) direct target phosphorylation (e.g. enzymes)
2) transcriptional regulation
3) translational regulation
4) autophagy

48
Q

TOR

A
  • induced translation initiation S6 kinase
  • induced rRNA transcription (ribosome biogenesis)
  • suppresses autophagy (ATG13 inactivation)
49
Q

SnRK1

A
  • transcriptional reprogramming
  • bZIP, MYC2 TF phosphorylation
  • represses ribosomal proteins
  • aa degradation, gluconeogensis
  • induces autophagy (ATG1, ATG6)
  • represses enzymes
  • isoprenoid biosynthesis, nitrate assimilation, starch synthesis
50
Q

Hormonal component of stress:

A

Abiotic: ABA
Biotic: SA, JA, ET

51
Q

Stress combination

A
  • synergistic
  • neutral
  • antagonistic effects
  • abiotic stresses activate different can influence biotic outcome
52
Q

Drought in Solanum dulcamara

A
  • Increased R to insect herbivore
  • flooding had no effect
53
Q

Drought in A. Thaliana

A
  • decreased resistance to Pseudomonas syringae PV tomato DC3000

B3.0 (23 decks)

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