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B3.0 > Drought Stress I > Flashcards

Drought Stress I Flashcards

1
Q

Drought

A

The single most common cause of severe food shortages in developing countries

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2
Q

Dessication

A
  • extreme water loss
  • when tissue equilibrates to ψ of air (<=-100MPa)
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3
Q

Avoidance

A
  • maintains constant ψ
  • flowering during/after rains in deserts
  • succulence
  • CAM photosynthesis
  • etc.
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4
Q

Tolerance

A
  • equilibrate cellular and ambient ψ: ψ changes
  • withstand and recover
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5
Q

Vegetative desiccation tolerance

A
  • ancestral
  • most bryophytes are dessication-tolerant
  • lost in moss stem lineage
  • c0.2% in angiosperms (Craterostigma pumilum)
  • most seeds and pollen are dessication tolerant
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6
Q

Principles driving water movement

A
  • high -> low ψ
  • root = 0.3
  • stem = liquid column, highly cohesive molecules
  • air = -100
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7
Q

Short distance water movement

A

Diffusion, osmosis

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8
Q

Long distance water movement

A
  • tension caused by evaporation
  • bulk flow under pressure
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9
Q

Factors affecting water movement @ root

A

1) soil properties
2) architecture
3) cell wall permeability
4) plasmodesmata
5) aquaporins

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10
Q

Factors affecting water movement @ stem

A

Xylem anatomy - Tradeoff safety/efficiency

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11
Q

Factors affecting water movement @ leaf

A

1) leaf vein patterning
2) guard cell density and opening

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12
Q

Xylem structure affects water transport

A
  • larger elements:
  • higher conductance + water vol
  • embolism
  • cavitation
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13
Q

Why is drought a stress?

A
  1. Oxidative
  2. Low energy
  3. Osmotic
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14
Q

Drought oxidative stress

A

ROS formation

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15
Q

ROS formation

A
  • membrane damage
  • protein aggregation
  • photosynthetic impairment
  • other cellular functions
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16
Q

Drought as low energy stressor

A

CO2 limitation

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17
Q

Drought as osmotic stressor

A
  • membranes and cell walls break and adhere to
  • protein aggregation/denaturation
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18
Q

Vacuole

A
  • most water stored here
  • provides positive turgour pressure that supports tissues
  • 0.5-1.5MPa
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19
Q

Water limitation

A
  • < turgour pressure
  • tissues wilt
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20
Q

Osmosensing

A
  • 2x component regulatory system
  • Arabidopsis histidine kinase I (AHKI)
  • ABA
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21
Q

Osmosensing pathway

A

1) oxygen signal: AHK1 autophopshorulation
2) starts H-D-H-D photo relay activating response regulator(s)
3) drought induced ABA transcription

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22
Q

AHK1

A
  • putative PM osmosensor
  • OX = drought tolerance in Arabidopsis
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23
Q

Mechanically activated ion channels

A
  • activated by membrane deformation
  • channels turn mechanical force into ion flux
24
Q

OSCA/TMEM63 family

A
  • hyperosmolarity-gated Ca2+ channels @ PM
  • mutant: lacks drought-induced early Ca2+ spikes; more sensitive to osmotic stress
25
Q

OSCA OX

A
  • increased drought tolerance in different species of Arabidopsis
26
Q

MCA1/2

A

Additional PM localised Ca2+ channels linked to drought stress

27
Q

MSLs, PIEZO, TPK1

A
  • Ca2+ channels localised to organelles membrane
  • linked to drought stress
28
Q

Signal transduction

A

Can be ABA-(in)dependent

29
Q

ABA

A
  • basal in all cells
  • increases rapidly in leaves upon osmotic stress
  • synthesis in plastid + cytoplasm
  • from carotenoids
30
Q

NCED3

A

Expression induced ABA

31
Q

Polymerisation-induced BGI

A

Deconjugates and activates ABA

32
Q

Plants that cannot close their stomata

A
  • lose turgour and wilt
  • e.g. ABA- deficient tomato (notabilis)
33
Q

Short term responses

A
  1. Water balance
  2. Protection
34
Q

Water balance

A
  • decrease water loss by stomatal closure
  • increase water uptake by osmolyte production (AAs, sugars, proline)
  • increased Aquaporin activity
35
Q

Protection

A

Against protein misfolding and membrane leakage
- LEA proteins
- chaperones
- antioxidant systems

36
Q

Direct regulation

A

Transporters, enzymes

37
Q

Indirect regulation

A

Gene expression

38
Q

No ABA signalling

A
  • ABCG40: not activated
  • no PYR/PYL activation
  • PP2Cs active
  • SnRK2s blocked
  • guard cells remain turgid
39
Q

ABA signalling

A
  • ABCG40 R activated
  • PYR/PYL activated
  • PP2Cs blocked
  • SnRK2s active
  • NADPH oxidase activated: ROS
  • ROS activate Ca2+
  • extracellular ion flux means turgidity lost
  • flaccid; pore closes
40
Q

TF regulation

A
  • 2 pronged approach
  • PYR/PYL enters nucleus
  • blocks PP2Cs
  • SnRK2s phosphorylate TFs
41
Q

Drought TFs

A

1) osmolyte production
2) aquaporins
3) antioxidants
4) growth adjustments

42
Q

Drought-induced transcriptional reprogramming

A

Thousands of genes

43
Q

cis-acting promoter elements

A
  • ABRE motif
  • DRE motif
44
Q

ABRE motif

A
  • Present in promoter of 82% dehydration-responsive genes in Arabidopsis
  • bound by AREB/ABF TFs
45
Q

DRE motif

A
  • bound by DREB TFs
  • ABA-independent
46
Q

DRE motif

A
  • bound by DREB TFs
  • ABA-independent
47
Q

Osmoticum

A
  • water-soluble, osmotic compound
  • does not interfere w metabolism
  • contributes to cellular water retention
48
Q

Proline

A
  • biosynthesis induced by ABA
  • synthesised from glutamate in chloroplast
  • transported into cytosol
  • degraded in mitochondria
49
Q

Proline functions

A

1) osmolyte: ^ cell turgour
2) stabiliser: molecular chaperone; protects protein and membrane integrity
3) ROS scavenger
4) redox regulator -> buffers cytosoluc pH to maintain state

50
Q

Aquaporins

A
  • channel-forming TM proteins
  • facilitate water movement across membranes
  • regulated (post)-transcriptionally
51
Q

LEA proteins

A
  • accumulate for protection of cell structures eg membrane
  • intrinsically disordered
  • water deficit: folded α-helix
52
Q

LEA functions

A

1) sequester (H2O, sugar, ions, ROS)
2) molecular chaperone

53
Q

Antioxidants

A
  • ^ capacity
  • scavenge ROS
54
Q

Enzymatic antioxidants

A

SOD
APX
GPX
GST
CAT

55
Q

Non-enzymatic antioxidants

A

AA, GSH, α-tocopherol, carotenoids, phenolic, flavonoids, proline

B3.0 (23 decks)

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