Plants and Water Flashcards
Where does the ATP required for stomatal opening come from?
- Mitochondrial oxidative phosphorylation
2. Chloroplastic photophosphorylation
What is the relationship between NR-staining bodies and stomatal aperture?
Inverse relationship
When stomata open, lipid droplet (NR-staining bodies) reduce in abundance
What is the driving force for transpiration?
It is the evaporation of water at the leaf surface that provides the driving force for transportation
Three pathways for water movement
- Transmembrane
- Symplastic (through plasmodesmata)
- Apoplastic (through cell walls, not cells)
What do endodermal cells have covering them and why?
A casparian strip
It prevents water and nutrients entering the xylem by the apoplastic pathway, but not the symplastic or transmembrane pathways
Why must water and nutrients enter and pass through the endodermal cell before entering the xylem?
It provides a selectivity filter (important for nutrients) and stops water leaking back from the xylem
Why is it important that stomata control evapotranspiration and CO2 uptake?
- Water and mineral supply
- Leaf cooling
- Ability to withstand drought
- Photosynthesis and dry matter accumulation
- Signal integration
How large is the stomatal pore when fully open?
20 micrometers
How many stomata per square mm of epidermis in Arabidopsis?
150
What signals cause stomata to open?
High relative humidity
High light
Blue light
Low CO2 concentration
What signals cause stomata to close?
ABA
Darkness
High CO2 concentration
Low relative humidity
What do guard signals do as a response to environmental signals?
Guard cells integrate information from environmental signals to ‘set’ the most appropriate stomata aperture for the prevailing conditions
Must balance need for CO2 uptake with requirement to restrict water loss
How do external signals cause stomatal aperture changes?
Extracellular signals - plasma membrane events - cytosolic coupling events - alterations to membrane trafficking / ion transport / metabolism / gene expression / cytoskeleton - changes in stomatal aperture
Response of guard cells to reduced relative humidity?
(ABA signalling pathway)
Once ABA is bound to its receptor, it sets off a chain of events that lead to the control of ion channels. To bring about stomatal closure, K+ ions must be lost from the guard cell. Water will follow the K+ ions and leave the guard cell, and its turgid decreases
-ABA receptor results in activation of ion channels which leads to increase of concentration of calcium ions inside the cell and the activation of kinases which phosphorylate their substrates
-Final channel GORK is where potassium leaves cells, and is activated by membrane depolarisation triggered by loss of anions from these channels
How to determine what genes are involved in responses to reduced atmospheric relative humidity
Isolation of mutants involved in responses to reduced atmospheric RH
What proteins are involved in responses to reduced atmospheric relative humidity
ost1 (SnRK2) protein kinase known to be involved in ABA-induced stomatal closure
aba2 - an enzyme involved in ABA synthesis
What percentage loss of K+ ions should a guard cell lose when exposed to dry air? (Who wrote the paper)
30%
Bauer et al., 2013
How was the response of guard cells to high CO2 concentrations tested?
Chater et al., 2015
Used mutants where the ABA receptor genes had been knocked out (pyr1pyl1,pyl4 and pyr1pyl1,pyl2,pyl4) and the nced3nced5 double mutant that fails to make ABA
Then tested whether these mutants closed in response to high CO2 concentrations
Showed that CO2-induces closure requires ABA and ABA receptors
