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
What group of plants have no stomata
Liverworts
What are the most primitive plant groups with stomata?
Mosses and Hornworts
Oldest fossil which contains stomata
Cooksonia
420 Mya
Stomata have very similar morphology but no intermediate types have been found in fossil
Poor stomatal fossil record
When did Lycophytes emerge?
Example of species with stomata
c400 Mya Selaginella uncinata (stomata on microphylls)
What does light-induced stomatal opening and reductions in lipid droplet abundance involve?
PHOT1 and PHOT2
Why is there a reduction in lipid droplets during stomatal opening? (hypothesis)
Triacylglycerols (TAGs - storage glycerols) are broken down and metabolised to produce the ATP required in stomatal opening
The process is called beta-oxidation and it occurs in a cellular organelle known as a peroxisome
What is a peroxisome?
Small organelle which contains the reducing enzyme catalase and some oxidases
How to determine if beta-oxidation is vital in the process of stomatal pore opening?
Take mutants which are compromised in the beta-oxidation process and see if they show light-induced stomatal opening
What is SDP1?
Encodes TAG ligase which helps to break down TAG
What is observed in sdp1 and cts1 mutants? How can this be phenocopied?
Delayed light-induced stomatal opening
Phenocopied by beta-oxidation inhibitor DMP
What does cts encode?
ABC transporter protein
What happens to the activity of H+-ATPase in mutants where less TAG is hydrolysed so there is less ATP available?
The activity of H+-ATPase is reduced, so the pH of the guard cell takes longer to lower as H+ ions remain in the cytoplasm
Increased demand for energy by 2030
50%
IEA
Increased demand for water by 2030
30%
IFPRI
Increased demand for food by 2030
50%
FAO
Up to what % of water taken into a plant is lost by evaporation from leaves?
97%
What is WUE?
Water use efficiency
What is stomatal conductance
The rate of passage of CO2 (mmol m^-2 s^-1) entering or water exiting through the stomata of a leaf
What is relationship between transpiration and stomatal conductance
Positive linear relationship
How can conductance be reduced without a negative effect on WUE?
Net CO2 assimilation saturates at high conductance
A reduction in stomatal conductance to level where reduction of net CO2 assimilation is minimised but transpiration is greatly reduced, the UWE will improve
What is an EPF?
Epidermal patterning factor
How is stomatal development controlled?
A family of secreted peptide signals known as EPFs bind to a cell surface receptor. Binding activates an intracellular MAP kinase cascade, which phosphorylates a transcription factor required for cells to develop into stomata
What are EPF1 and EPF2?
Inhibitors: a mutant lacking EPF1 and EPF2 (epf1epf2) has increased stomatal development while plants that over-express EPF1 and EPF2 (EPF1OE and EPF2OE) have decreased stomatal development
What is EPFL9?
Activator: plants with reduced EPFL9 (EPFL9RNAi) have decreased stomatal development whilst plants overexpressing EPFL9 (EPFL9OE) have increased stomatal development
Plants with what mutations have very high stomatal development
epf1eof2EPFL9OE
How to compare water loss among EPF plants? Why?
Use infrared thermal imaging (as a proxy measure for transpiration)
To test the effect of stomatal density in plant water loss
Which mutant line had a higher WUE?
Arabidopsis EPF2-OE line - reduced density of larger stomata
