5. Short-term responses to drought

Question 1

Overview of this lecture

Answer 1

1. Water-plant relations
2. The global drought stress
3. Perception: Osmosensors
4. Signalling: ABA
5. Response: Water uptake and protection

Question 2

How are plants tolerant to drought across the tree of life?

1.1

Answer 2

Plants can be poikilohydric or homoiohydric. Poikilohydric plants are resistant to drought. Resistant plants can be either avoidant or tolerant. Dessication tolerance has been lost through evolutionary time, with most bryophytes being dessication tolerant, and only 0.3% of angiosperms being dessication tolerant.

Question 3

How does water travel through a plant?

1.2

Answer 3

Water travels from root to shoot via the xylem, and always moves from higher to lower water potential.

Question 4

What different factors affect water movement within a plant?

1.3

Answer 4

1. Soil: Root architecture, cell wall permeability, plasmodesmata, aquaporins, soil
2. Xylem: Anatomy of xylem, WP. However, larger xylem are more prone to embolism and cavitation.
3. Leaf: Vein pattern, guard cell density. plasmodesmata, aquaporins

Question 5

What are the 3 major stressors from drought?

2.1

Answer 5

Oxidative. Low-energy. Osmotic.

They are all highly interactive.

Question 6

What is the impact of oxidative stress on a plant?

2.2

Answer 6

Generated by stomatal closure. Causes the accumulation of ROS formation, which is toxic to the cell, and leads to protein, lipid and DNA damage, as well as cellular dysregulation. Regulated by MAPKs

Question 7

What is the impact of low-energy stress on a plant?

2.3

Answer 7

Leads to a reduction in photosynthesis due to CO2 limitations. Promotion of survival over growth. Regulated by SnRK1/TOR

Question 8

What is the impact of osmotic stress on a plant?

2.4

Answer 8

Fusion or stretching of membranes in unusual places. Proteins may aggregate or denature. Controlled by SnRK2-ABA.

Question 9

How do osmoreceptors perceive stresses?

3.1

Answer 9

Osmoreceptors forms a two-component regulatory system. The histidine kinase protein AKH1 initiates a phosphate signalling cascade to induce drought-transcribed ABA. Osmosensors then mechanically activate ion channels via deformation, using the OSCA/TMEM63 family, which transmit this signal

Question 10

How does ABA signal drought stress?

4.1

Answer 10

Can be either ABA-dependent or independent. Both of these responses will interact. ABA signalling leads to TF regulation, leading to changing gene expression in osmolytes, aquaporins, antioxidants and growth adjusters.

Question 11

How can ABA lead to transcriptional reprogramming?

4.2

Answer 11

Action on cis-acting promoters, such as ABRE- and DEF- motifs

Question 12

What are the two main responses to drought?

5.1

Answer 12

Water balance. Protection.

Question 13

What are the main ways plants respond to drought via changing water uptake?

5.2

Answer 13

Reduction of water loss.
Osmotic adjustment.
Increase in aquaporin expression/activity.

Question 14

How do plants reduce water loss?

5.3

Answer 14

Use of ABA, which regulates guard cells. ABA binds to ABCG40, which binds to PYR/PYL, which binds to PP2C. This represses SnRK2, which directly controls ion transport channels, and decreases water potential of cells outside guard cells. Movement of water outside guard cells. Flaccidity.

Question 15

How do plants adjust their osmolarity?

5.4

Answer 15

1. Movement of inert molecules into cytoplasm (called the osmoticum)
2. Movement of inorganic salts into the vacuole

Proline is an important osmoregulator, and is also used as a redox scavenger and molecular chaperone

Question 16

How is aquaporin expression/activity changed in plants?

5.5

Answer 16

Aquaporins are intrinsically disordered proteins folded into alpha-helices when subject to water deficit. This shape allows for more efficient water transport, and facilitates water movement.

Regulation occurs pre- and post-transcription

Question 17

What are the two protective responses that plants produce to drought?

6.1

Answer 17

Increase in LEA protein accumulation. Increase in antioxidant capacity.

Question 18

How do plants change their LEA protein levels as a protective response?

6.2

Answer 18

Increase in LEA protein accumulation. Has three major responses.
1. Increases the local sequestration of some molecules
2. Membrane protection
3. Acts as a molecular chaperone

Question 19

How do plants use ROS as a protective drought response?

6.3

Answer 19

Scavenging and improving ROS to limit damage. Use of enzymatic and non-enzymatic anti-oxidants.