Chapter 16 - Plant responses Flashcards
What is tropism?
A plants response to abiotic factors
What are some roles of auxin?
Control of cell elongation, preventing abscission, apical dominance and stimulates ethene release
What are some roles of gibberellins?
Causes stem elongation, stimulates pollen growth and triggers mobilisation of food stores in germination
What are some roles of ethene?
Causes fruit ripening and promotes abscission (in deciduous trees)
What are some roles of ABA?
Maintains dormancy, stimulates protective responses and stimulates stomatal closing
What is the process of seed germination?
- Absorbed water activates the embryo and gibberellins are produced
- Digestive enzymes are stimulated to break down food stores
- Food stores used to produce ATP so the plant can break through the seed coat
Experimental evidence of gibberellins role in germination:
- Biosynthesis inhibitors stop germination, if gibberellins reapplied, germination continues
- Mutant seeds without gibberellins don’t germinate unless external gibberellins are applied
What is apical dominance?
The apical bud on the tip of the plant stem has dominance over other lateral buds on the stem, if apical bud is removed, the lateral buds have a higher yield of auxin than before which allows them to grow more
What is effected by high concentrations of auxin?
- Lateral shoots become suppressed to growth, leading to apical dominance
- Inhibitory of root growth
What is effected by low concentrations of auxin?
Promoted root growth (unless apical bud is removed)
What effect do gibberellins have on plant stems?
Allow stems to grow at increased rates in darkness and stem elongation by increasing the length of internodes
What effect does auxin have on plant stems?
Auxin effects the growth of the apical shoot and the direction of growth
What is synergism?
When multiple plant hormones act together to create a greater response
What is antagonism?
The balance between two hormones that have opposite effects
What is the process of abscission?
- As light levels decrease, auxin concentration decrease
- Lower auxin conc. produce ethene that initiates gene switching in abscission zone
- Vascular bundles sealed off and fatty acid is deposited in cells of the separation layer (protective layer)
- Low temperature and strong winds finish the process (strain breaks off the leaf)
How do plants prevent themselves from freezing?
Roots store salt, sugar and antifreeze proteins which prevent the cells from becoming frigid in colder temperatures
How are the stomata controlled by the plant?
- ABA controls stomata under abiotic stress
- Root cells detect low water availability and release ABA
- ABA is transported to the leaves, causing guard cells to become turgor and close over the stomata, preventing water loss
What are the three main responses to herbivory?
Physical, chemical and pheromones
What are the chemical responses of herbivory?
Tannins -
Alkaloids -
Terpenoids -
What are pheromones?
Chemicals made by an organism which affects the social behaviour of other members within the species or be used to defend the organism
What is phototrpism?
A plants response to light (eg. by bending towards it)
What is photoperiodism?
- A plants sensitivity to a lack of light, triggering change
- Plants have light sensitive pigments called phytocrhromes (Pr and Pfr) which alter depending on light levels
What is thigmotropism?
A plants physical response to touch (eg. leaves curling up)
What is geotropism?
A plants physical response to gravity (eg. roots growing downwards)
