6. Long-term responses to drought Flashcards
Structure of the lecture
- Response: Altering source-sink dynamics
- Response: Escaping drought
- Comparison: Long- and short- term responses
- Improvements: Agricultural technologies
- Improvements: Biological methods
- Improvements: Genetics
What are the four major methods that source-sink dynamics are altered in long-term drought responses?
1.1
- Induction of water uptake
- Hydraulic acclimation
- Reduction of water loss
- Improved water resource use
How is water-uptake increased in changing source-sink dynamics?
1.2
- Root tropisms, and patterning towards water
- Increase in primary root growth
What is the mechanisms between changing root tropisms?
1.2.1
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
How can hydraulic acclimation be used to alter source-sink dynamics?
1.3
- Secondary cell wall reinforcement
- Increased number of xylem vessels
- Reduced diameter of xylem vessels
How can the diameter of xylem vessels be reduced to allow for hydraulic acclimation?
1.3.3
ABA signalling in the endodermis results in thinner cell walls, enhancing water entry into embolised vessels
How can water loss be reduced, in order to change source-sink dynamics?
1.4
- Suberisation of the endodermis
- Reduced root growth
- Reduced leaf surface
- Leaf abscission
How does suberisation of the endodermis occur to reduce water loss?
1.4.1
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
How can root growth be reduced to decrease water loss?
1.4.2
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
How can leaf surface be reduced in order to reduce water loss?
1.4.3
New leaves are smaller, with a lower stomatal density and a thickened waxy cuticle. Reduces water loss via transpiration
What is a tactic that plants use to escape drought?
2.1
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
Comparison of reduction transpiration in long and short term responses
3.1
Short term: Stomatal closure through SnRK2/ABA
Long term: Changes to leaf surface through waxy cuticle, fewer stomata and smaller leaves
Comparison of water uptake in long- and short-term responses to drought
3.2
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)
Two improvements we can make agriculture against drought stress
4.1
- Partial Root Drying Zone
- Plant monitoring
What is a Partial Root Drying Zone technique?
4.2
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.
