6. Long-term responses to drought

Question 1

Structure of the lecture

Answer 1

1. Response: Altering source-sink dynamics
2. Response: Escaping drought
3. Comparison: Long- and short- term responses
4. Improvements: Agricultural technologies
5. Improvements: Biological methods
6. Improvements: Genetics

Question 2

What are the four major methods that source-sink dynamics are altered in long-term drought responses?

1.1

Answer 2

1. Induction of water uptake
2. Hydraulic acclimation
3. Reduction of water loss
4. Improved water resource use

Question 3

How is water-uptake increased in changing source-sink dynamics?

1.2

Answer 3

1. Root tropisms, and patterning towards water
2. Increase in primary root growth

Question 4

What is the mechanisms between changing root tropisms?

1.2.1

Answer 4

Xerobranching and xerotropisms allow for the increased vertical growth through the soil to deep water. Hydrotropisms are regulated by auxin. Hydropatterning (root branches) is regulated by ABA

Question 5

How can hydraulic acclimation be used to alter source-sink dynamics?

1.3

Answer 5

1. Secondary cell wall reinforcement
2. Increased number of xylem vessels
3. Reduced diameter of xylem vessels

Question 6

How can the diameter of xylem vessels be reduced to allow for hydraulic acclimation?

1.3.3

Answer 6

ABA signalling in the endodermis results in thinner cell walls, enhancing water entry into embolised vessels

Question 7

How can water loss be reduced, in order to change source-sink dynamics?

1.4

Answer 7

1. Suberisation of the endodermis
2. Reduced root growth
3. Reduced leaf surface
4. Leaf abscission

Question 8

How does suberisation of the endodermis occur to reduce water loss?

1.4.1

Answer 8

ABA induction of suberisation (via suberin), which insulates the vasculature and minimises water loss

Tested in dry environment accessions of A. thaliana by Feng et al., 2022

Might be regulated by the GPAT6 gene

Question 9

How can root growth be reduced to decrease water loss?

1.4.2

Answer 9

Low ABA concentrations leads to low meristem production.

Note: this is only for severe cases of drought. Normally, primary root growth would increase to try to access more water

Question 10

How can leaf surface be reduced in order to reduce water loss?

1.4.3

Answer 10

New leaves are smaller, with a lower stomatal density and a thickened waxy cuticle. Reduces water loss via transpiration

Question 11

What is a tactic that plants use to escape drought?

2.1

Answer 11

Induction of the reproductive phase transition. Induction of early flowering through ABA-mediated regulation of the photoperiod-floral induction pathway.

Means that there is a rapid production of seeds to allow for reproduction, despite drought

Question 12

Comparison of reduction transpiration in long and short term responses

3.1

Answer 12

Short term: Stomatal closure through SnRK2/ABA
Long term: Changes to leaf surface through waxy cuticle, fewer stomata and smaller leaves

Question 13

Comparison of water uptake in long- and short-term responses to drought

3.2

Answer 13

Short term: Use of osmolytes and osmotic adjustments, and increasing aquaporins

Long term: Primary root growth via ABA. Adjustments to xylem (increase in number, reduction in diameter)

Question 14

Two improvements we can make agriculture against drought stress

4.1

Answer 14

1. Partial Root Drying Zone
2. Plant monitoring

Question 15

What is a Partial Root Drying Zone technique?

4.2

Answer 15

Plants are watered on alternating sides to allow for xerobranching and xeropatterning as a drought response, and extended roots. Equivalent, large roots as a drought response. Higher yield.

Question 16

How can we use monitoring to improve agriculture in the face of drought?

4.3

Answer 16

Use of thermal imaging to make drought maps and inform precision farming. Allows for photosynthesis related measurements

Question 17

What is osmopriming

5.1

Answer 17

Induction of a ‘drought memory’. Allows for the modulation of plant-water relations, root architecture and osmolytes.

Marthanda et al., 2020 showed it had success in wheat/barley/sorghum/caraway

Question 18

Possible future areas for research into biological methods to improve agriculture?

5.2

Answer 18

Osmotic adjustment, regulation of stomatal conductance of CO2, water-use efficiency, photosynthetic rates, delays in senescence, root architecture, regulation of the reproductive phase

Question 19

Methods to identify potential genes for editing?

6.1

Answer 19

Forward: Observing natural genetic phenomena and searching for drought tolerance/comparing to non-drought tolerance

Reverse: Looking at the genome and trying to find genes for drought tolerance

Question 20

Methods for genetic engineering through breeding

6.2

Answer 20

Conventional: Selectiv breeding
Molecular: Use of QML

Question 21

Potential limitations to breeding technologies

6.3

Answer 21

Does research apply to the crop of interest? Does research work in field? Are there many drawbacks?