The effects of plant hormones Flashcards
What is apical dominance?
When auxins stimulate apical bud growth,
but inhibits growth of side shoots from lateral buds
What happens when the apical bud is removed?
Auxins stops being produced, and the side shoot formation is no longer inhibited.
What are the control variables for apical dominance practical?
light intensity, temperature, water
you leave all the plants to grow for 6 days
What do gibberellins do? (4 things)
Stimulate
1) seed germination
2) stem elongation
3) side shoot formation
4) Flowering
How do gibberellins stimulate seed germination?
They trigger the break down of starch into glucose
The glucose is then used to respire and release energy it needs to grow
What inhibits gibberellins ?
Abscisic acid.
For the apical dominance practical :
30 plants total
10 with removed tip and auxin paste
10 with removed tip and without auxin paste
10 with no change ( “control” to compare)
Gibbering stem elongation practical:
40 plants in total
- 20 plants leave normal, water the normally and keep conditions same
- The other 20 plants, leave them to grow normally, BUT
water them with a dilute solution of gibberellin - Results suggest that gibberellins stimulate stem elongation
^ the ones watered with gibberellins have longer stems
(LET PLANTS GORW FOR 28 DAYS)
Are auxins and gibberellins synergistic or antagonistic?
BOTH
What does synergistic mean?
It means the auxins and gibberellins can work together and have a really big effect.
What does antagonistic mean?
Means that auxins and gibberellins can sometimes oppose each others actions.
E.g. Gibberellins stimulate side shoot formation, but auxins inhibit side shoot formation.
What are deciduous plants?
Plants that lose their leaves
Why do plants lose their leaves?
To conserve water during cold parts of the year
- where, it is a lot harder to absorb water from the frozen soil
- there is also less sunlight available for photosynthesis
What hormones control leaf loss?
Auxins and ethene
How do auxins control leaf loss?
Auxin inhibits leaf loss
However as a leaf gets older less auxin is produced, so there is more leaf loss.
How does ethene control leaf loss?
A layer of cells called the abscission layer develops at the bottom of the leaf stalk.
- The abscission layer separates the leaves from the rest of the plant.
ETHENE CAUSES the abscission layer to expand, breaking the cell walls causing LEAF LOSS.
What hormone triggers the stomata to close?
Abscisic acid ( ABA)
How does abscisic acid trigger “stomatal closure” ?
ABA binds to the receptors on the membrane of the guard cells.
- This causes ion channels to open which allows calcium ions to move from the vacuole into the cytosol.
- High concentration of calcium ions int he cytosol causes other ion channels to open.
- It is this that causes things like potassium ions to leave the guard cells through ion channels increasing the water potential of the guard cells
- WATER LEAVES the guard cells by osmosis, guard cells become flaccid and the stomata closes.
How can ethene be used commercially ( fruit industry)
- Ethene stimulates BREAK DOWN of cell walls, chlorophyll and converts starch into sugars.
- This makes fruit soft and ripe and ready to eat.
How can auxins be used commercially ( farmers and gardeners)
2 ways
1) Used in selective weed kills ( herbicides)
2) Used as rooting hormone in rooting powder
How is auxin used in weed killers?
Auxins make weeds produce long stems, so weeds grow tall, so they can’t manage to get enough water or nutrients SO THEY DIE
How is auxin used in rooting powder?
- auxins make a cutting grow roots
- The cutting can be planted and grown into a new plant.
- Many cuttings can be taken from one plant, and can be treated with rooting hormones, so lots of the same plant can be grown quickly and cheaply from one plant.
