Plant Stress Responses

Question 1

Stress

Answer 1

• 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)

Question 2

Abiotic:

Answer 2

• 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

Question 3

Biotic:

Answer 3

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

Question 4

Acclimation

Answer 4

• 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)

Question 5

Adaptation

Answer 5

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

Question 6

Stress response:

Answer 6

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

Question 7

Types of stress response curves

Answer 7

• essential + non-essential environmental factors

Question 8

Essential environmental factors

Answer 8

• optimal range
• sub- (deficiency), supra- (excess)

Question 9

Non-essential environmental factors

Answer 9

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

Question 10

Strategies of stress responses

Answer 10

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

Question 11

Drought tolerance

Answer 11

Selaginella lepidophylla “resurrection plants” lose 90% cellular water

Question 12

Freezing tolerance

Answer 12

Antifreeze protein accumulation to control ice crystal growth

Question 13

Drought avoidance

Answer 13

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

Question 14

Freezing avoidance

Answer 14

Senecio keniodendron (giant groundsel) folds leaves to insulate meristem

Question 15

Phases of stress acclimation

Answer 15

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

Question 16

Stress priming

Answer 16

• short and long term memory
• trans-generational under debate

Question 17

Stress priming depends on

Answer 17

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

Question 18

Memory genes

Answer 18

Higher expression during stress

Question 19

Stress responses can

Answer 19

• involve extra/intracellular single d
• be specific/general

Question 20

Process of stress response

Answer 20

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

Question 21

General responses

Answer 21

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

Question 22

General protection

Answer 22

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

Question 23

Specific responses

Answer 23

• to particular stress types
• signals + components

Question 24

Specific protection

Answer 24

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

Question 25

ROS

Answer 25

- 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

Question 26

ROS production

Answer 26

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

Question 27

Enzymatic antioxidants

Answer 27

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

Question 28

Apoplast

Answer 28

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

Question 29

Ca2+ signals

Answer 29

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

Question 30

Ca2+ signals affect

Answer 30

- metabolism - transcription - transport - et al

Question 31

Long-distance signalling via ROS/Ca2+ waves:

Answer 31

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

Question 32

Stress signals

Answer 32

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

Question 33

Systemic ROS/Ca2+ wave propagation and

Answer 33

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

Question 34

RICR

Answer 34

- apoplastic ROS activate PM calcium channels - ^ cytosolic Ca2+ conc - Ca2+ -> plasmodesmata

Question 35

CICR

Answer 35

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

Question 36

ROS/Ca2+ waves

Answer 36

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

Question 37

ROS/Ca2+ Co-signals

Answer 37

- pH - membrane potential - metabolites - hormones - eATP

Question 38

Systemic ROS

Answer 38

2’-7’-dichlorodihydrofluorescin diacetate

Question 39

Ca2+

Answer 39

Flourescence

Question 40

Different stresses lower energy production

Answer 40

- shading, pollution, drought, salinity, heat, cold, flooding - SnRK1: crucial for stress tolerance

Question 41

SnRK1, SNF1, AMPK

Answer 41

- ^ energy production (catabolism, Autophagy) - < energy consumption (anabolism, translation/growth)

Question 42

Low sucrose sugar status (stress!)

Answer 42

- SnRK1 inhibits TOR kinase (growth agonist)

Question 43

High sucrose sugar status (optimal)

Answer 43

- sucrose inhibits SnRK1

Question 44

Plants have to balance

Answer 44

- growth (anabolism, developmental progression) - survival (catabolism, nutrient mobilisation, stress responses)

Question 45

Tradeoff:

Answer 45

^SR =

Question 46

Energy sensing pathways

Answer 46

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

Question 47

TOR

Answer 47

- induced translation initiation S6 kinase - induced rRNA transcription (ribosome biogenesis) - suppresses autophagy (ATG13 inactivation)

Question 48

SnRK1

Answer 48

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

Question 49

Hormonal component of stress:

Answer 49

Abiotic: ABA Biotic: SA, JA, ET

Question 50

Stress combination

Answer 50

- synergistic - neutral - antagonistic effects - abiotic stresses activate different can influence biotic outcome

Question 51

Drought in Solanum dulcamara

Answer 51

- Increased R to insect herbivore - flooding had no effect

Question 52

Drought in A. Thaliana

Answer 52

- decreased resistance to Pseudomonas syringae PV tomato DC3000