Hormones and sensing Flashcards
(25 cards)
How do plants adapt to changing environmental conditions?
Meristematic cells give them morphological plasticity to maximise access to light / water / nutrients
Photomorphogenesis is a response to:
Amount + colour of light
Phototropism is a response to:
Direction of light
Photoperiodism is a response to:
Duration of light
What does phytochrome respond to?
Red:Far-red ratio
Red light causes Pr_____
Pr(active)
Far-red light causes Pr_____
Pr(inactive)
Darkness causes Pr_____
Pr(inactive)
Phytochrome triggers:
De-etiolation
What happens when a seedling breaks through the surface?
Absorption of red light causes phytochrome activation, triggering a de-etiolation response
Define: etiolated
State of a plant in darkness, when it only focuses on stem elongation, without chlorophyll synthesis or root and leaf production
Photoperiodism determines:
Flowering time, bud dormancy
What does interruption of night cause?
P(fr)->P(r), preventing correct triggering of flowering
Phytochrome triggers production of:
Florigen, a hormone like signal which moves to the apex where it triggers flowering, as well as controlling bud dormancy over winter in deciduous plants
Define: gravitropism
Ability to sense gravity in plants - root grows up and shoot grows down
How does gravitropism occur?
Statolith hypothesis - dense starch grains precipitate to the lowest point in cells near the root tip, these appear to direct the direction of cell expansion
Define auxin:
Indole acetic acid (IAA), a growth promoting hormone that can cause plants to change their growth axis
What is the role of phototropin?
- A photoreceptor that mediates auxin distribution in the growing tip
- Affects the expression of PIN proteins, activating them on the shaded side and inhibiting on the sunny side
What is the role of auxin?
- Phototropism, causing the stem to bend towards the light by flowing down the shaded side of the stem and causing the cells to elongate
- Creates its own transport system by directing the formation of PIN proteins to carry it between cells
- Stimulating vascular differentiation to repair damaged tissue
- Flowing into developing leaves, in river like patterns that trigger vascular differentiation into leaf veins
- Apical dominance, basipetal flow inhibits axillary buds
What is the role of GA (giberellins/giberellic acid)?
- Important in controlling plant development
- Promotes (non-tropic related) cell elongation, deficiency causes dwarf plants, important in the green revolution
- Primary hormone involved in etiolation response
- High GA causes elongation, light (Pfr->Pr) triggers GA decline, causing de-etiolation
What is the role of ABA (abscissic acid)?
- Inhibitor of growth, usually associated with dehydration and salt stress, although has changed over time
- Activates desiccation tolerance in bryophytes
- Tracheophyte water stress reponse involves closing stomata, promoting leaf senescence, inhibiting stem growth, promoting root growth, increasing membrane stability in leaves
- Also plays a role in sex determination and seed dormancy
How does auxin cause stem bending?
- IAA promotes growth, and flows basipetally, creating PIN proteins to transport it between cells
- Phototropin activates PIN proteins on the shaded side and de-activates them on the sunny side
- This causes IAA to flow preferentially down the shaded side, causing greater elongation here and bending the tip towards the light
What hormonal processes occur in seed dormancy?
- Coordinated response between ABA and GAs
- ABA helps maintain dormancy
- Germination often stimulated by light and water
- Light activates phytochrome, water uptake promotes GA production
- This leads to amylase production, which converts starch to sugar and initiates growth
Define: ethylene
Gaseous hormone that promotes fruit ripening, regulates seedling growth, formation of root hairs, senescence
