Plant Hormones Flashcards
Examples of abiotic stress
Freezing
Drought
Increased soil water salinity
Presence of heavy metals e.g lead, copper
Ways plants respond to abiotic stress
E.g response to drought?
- dropping their leaves
- shutting their stomata (so reducing water loss via transpiration)
Others:
Some plants produce an antifreeze chemical in their cells, that decreases the formation of ice crystals that can destroy plant cells if allowed to form within them
What is herbivory
Consumption of plants by herbivores
Chemical defences to herbivory (& folding in response to it)
Alkaloids
Pheeonones
Tannins
What are tannins
What are alkaloids
What are pheromones
What are Nastic movements
What are tropisms
Growth movements of a part of a plant in response to a directional stimulus
Postive vs negative tropism
Towards vs against stimulus
5 types of tropisms table
How did darwin investigate phototropism and show that the tip detected light
How did scientists investigate tropisms using mica to show that the growth stimulus was a chemical that could travel through gelatin
How tropism was investigated (how the tip led to curvature)
Phototropism: how they found out it was due to a hormone by replacing the tip with a block
What does auxin do
Control growth elongation
What does auxin do
Control growth elongation
Where is auxin synthesised
The meristems (growing tips of roots & shoots)
Where does auxin move after it’s synthesised in the meristems
Passed down the stem to stimulate elongation / growth
Then, activates proteins in cell wall (expansins) which loosen bonds between cellulose microfibrils
Therefore, flexibility increases, so more elongation
Phototropism mechanism pic
Negative vs positive geotropism
Neg = shoots grow away from gravity
(Auxin accumulates on the lower side of the shoot, therefore grows upwards) This
Pos = roots grow towards gravity
In roots = higher IAA conc, so lower rate of elongation, as IAA accumulates at the lower side, therefore inhibiting cell elongation, so the lower side grows slower, so the root bends dowm
Investigating geotropism
What do deciduous plants do in very hot & dry conditions
Lose leaves to reduce water loss
What do deciduous plants do in winter
Lose leaves as water absorption is difficult due to frozen soils
Leaves shedded due to photosynthesis being limited by low temperatures and reduced light
What role does ethene play in leaf loss
Stimulates the breakdown of cell walls in the abscission layer, causing the leaf to drop of
What role does auxin / IAA play in leaf loss
Inhibit leaf loss & are produced in young leaves, making the leaves insensitive to ethene temporarily
The conc of IAA decreases as leaves age until leaf loss can occur
Main hormone that plays a role in stomatal closure?
ABA Abscisic Acid
Examples of water stress
High temperature
Reduced water supplies
What happens in times of water stress
ABA produced by plants to stimulate stomata closing
How does ABA work e.g. what does it bind to etc
- guard cells have ABA receptors on their cell surface membrane
ABA binds with these receptors, inhibiting the proton pumps & therefore stopping the active transport of H+ out of guard cells - ABA also causes Ca2+ ions to move into the cytoplasm of the guard cells, through the cell surface membrane
How do Ca2+ ions act as a chemical messenger to lead to stomatal closure
- Causes channel proteins to open, that allow negatively charged ions to leave the guard cells
-> this stimulates the opening of further channel proteins that allow K+ to leave the guard cells - Loss of ions = Increased W.P. Of guard cells, therefore water leaves via osmosis
Therefore
Guard cells become flaccid: stomata close
Role of gibberellins
- Control seed germination
- promotes fruit development
- promotes activity of amylase
Can also play a role in stem elongation
When the seed is shed from a parent plant is it active or inactive
- state of dormancy (metabolically inactive): little water
And can survive harsh weather
What does the seed contain
Endosperm (a starch containing energy store)
Embryo (which grows to the new plant when the seed germinates)
Aleurone layer (outer, protein rich layer)
What does the seed contain
Endosperm (a starch containing energy store)
Embryo (which grows to the new plant when the seed germinates)
Aleurone layer (outer, protein rich layer)
H2O absorbed = germination begins.
This stimulates the embryo to produce what hormone
Gibberellins
H2O absorbed = germination begins.
This stimulates the embryo to produce what hormone
Gibberellins
How do gibberellins molecules lead to amylase action
Gibberellins diffuses into the aleurone layer & stimulates the cells to synthesise amylase
How does amylase work to transport / give the embryo glucose
Amylase hydrolyses starch
Therefore soluble maltose produced
Maltose hydrolysed into glucose
Glucose transported to embryo
What breaks dormancy of the embryo
When the embryo respires the glucose given after amylase action
How does apical dominance happen
Commercial uses of plant hormones
- control ripening
- fruitless seed production
- hormone rooting powder
- hormonal weed killers
Other things specific hormones do
Ethene, auxin, cytokinins, gibberellins
How does ethene control ripening
How do auxins act as hormone root powders
How do synthetic auxins act as hormonal weed killers
Evidence for gibberellins role in germination and stem elongation
How would you investigate diff / conc plant hormone on growth
Use diff hormone
Use serial dilutions
How to investigate diff conc levels of hormone effect on plant
Factors to control when investigating plant hormone action
Volume of water
Light intensity
Temperature
Humidity
Ideally = genetically identical plants and cuttings to ensure they response the same way
Normal action of IAA in cells (ms answer)
Stimulates cell elongation & division
How can herbicides kill plants
By disabling proton pumps in a photosystem
-> reducing proton pumping & therefore chemiosmosis
-> photophosphorylation stops
-> less ATP produced
-> less NADP produced
-> no Calvin cycle stage
-> no TP/hexose sugars made
