Plant hormones Flashcards
What are plant hormones?
Chemical messengers that are synthesized in one part of the plant, transported to another part, then do something in the cells of the receiving plant part
What do hormones do at a cellular level?
They bind to receptors and activate signalling pathways
What is the usually the end result of a signalling pathway activated by hormones?
Activate or deactivate gene transcription, cause secretion of compounds, activate protein kinases
What are 5 ways a plant can get more of a hormone?
- Increased transportation to the receptive plant area
- Activate the biosynthesis pathway
- Activate an inactive form
- Release from internal stores
- Uptake from other plants
What are 4 ways a plant can reduce the amount of a hormone?
- Break it down
- Inactivate it
- Sequester it away from the receptors
- Excrete into the environment or to other tissues
What are the 9 major classes of plant hormones?
- Auxins
- Gibberellins
- Cytokinins
- Ethylene
- Abscisic acid
- Brassinosteroids
- Jasmonates
- Salicylic acid
- Strigolatones
Are auxins essential for plant survival?
Yes, deficient mutations are lethal
What is the principal auxin in plants?
IAA
What do auxins do?
Maintain apical dominance by suppressing lateral growth
What did Darwin’s phototropism experiment look at?
Directional response to light stimuli, to determine if the tip was coordinating the plant’s phototropism or if each cell was coordinating their own movements
What were the 4 conditions that Darwin tested in his phototropism experiment?
- Cut the tip off
- Opaque cap on the tip
- Transparent cap on the tip
- Covered the stem
What happened to the plant’s phototropism when the tip was cut off in Darwin’s phototropism experiment?
Didn’t grow towards the light
What happened to the plant’s phototropism when the tip was covered with an opaque cap in Darwin’s phototropism experiment?
Didn’t grow towards the light
What happened to the plant’s phototropism when the tip was covered with a transparent cap in Darwin’s phototropism experiment?
Grew towards the light
What happened to the plant’s phototropism when the stem was covered in Darwin’s phototropism experiment?
Grew towards the light
What did Went’s phototropism experiment address?
Was there a diffusible substance produced by the tip of the shoot that mediated plant’s growth and bending towards the light
What happened when Went replaced the tip of a seedling with a cut tip with an agar block saturated in the diffusible signal from the cut tip?
Growth resumed to the same level as the control
What happened when Went put the saturated agar block on one side of the stem?
The side in contact with the block grew faster
What effect does auxin have on a cell?
Activates a proton pump, which pumps protons into the cell wall and acidifies it
Why does the acidification of the cell wall caused by auxin allow it to expand?
The acidity activates expansin, which breaks the connections holding the fibrils together
How do plants move towards the light when signalled by auxin?
Auxin signalling causes cell walls to loosen on the side of the stem away from the light, so the stem bends towards the light
Where is auxin produced?
SAM, young leaves, developing fruits and seeds
How is auxin transported around the plant?
Through plasmodesmata and xylem
What are 4 functions of auxins?
- Cell differentiation for wound healing
- Apical dominance
- Fruit development
- Tropisms and other plant movements
When were gibberellins first discovered?
Foolish seedling disease in rice. Fungal pathogen was producing gibberellins and caused the plants to grow out of control and collapse
What are 3 functions of gibberellins?
- Cell elongation
- Cell division
- Seed dormancy and germination
Why do cells divide when you add coconut milk to them?
Contains cytokinins
What are 4 functions of cytokinins?
- Cell division
- Cell differentiation
- Senescence
- Apical dominance
What other hormone do cytokinins need to be in balance with to cause proper cell differentiation?
Auxins
Why were trees with nearby gas lamps entering senescence too early?
Gas lamps were producing ethylene
What are 2 functions of ethylene?
- Leaf abscission
2. Fruit ripening
Where is abscisic acid synthesized?
Vascular tissues
What are 4 functions of abscisic acid?
- Stress tolerance (water, heat, and salt stresses)
- Germination inhibition
- Symbiotic interactions
- Plant defence
