Plant Response Flashcards
what are the main plant hormones,
auxins
gibberellins
abscisic acid (ABA)
ethene
what is abscission
leaf fall
what is apical dominance
The auxins that are produced at the growing tip at the apex (i.e. the top) of a plant stem cause the stem to grow upwards and also stop lateral (side) buds from growing.
essentially it grows bent
role of auxins
- promote cell elongation in shoots
- prevent abscission
- maintain apical dominance
- involved in tropism
- stimulate ethene release
- involved in fruit ripening
role of gibberellins
- causes stem elongation
- stimulates seed germination & flowering
role of ABA
- maintains dormancy of seeds and buds
- stimulates cold protective responses ( antifreeze production)
- stimulates stomatal closing
role of ethene
- causes fruit ripening
- promotes abscission in deciduous trees
gibberellin’s and seed germination
the seed absorbs water, which activates production of gibberellins. It causes enzymes to be released which breakdown the food stores so that the embryo plant can use the food to respire and make atp
where is the food store for seed germination
cotyledons in dicot seeds
endosperm in monocot seeds
what evidence is there to suggest seed germination
- gibberellins ‘ switch on’ genes which code for amylases and proteases (digestive enzymes)
- ABA acts as an antagonist which interferes with the action of gibberellins
- mutant varieties of seeds have been bred which lack the gene enabling them to make gibberellins so those seeds cannot germinate unless gibberellins has been applied externally
- gibberellin biosynthesis inhibitors can be applied to seeds preventing germination as they cannot make gibberellins.
what plant hormone stimulates shoot growth and results in apical dominance
Auxins
auxins and apical dominance
how?
high and low conc
auxins inhibit lateral shoot growth due to the high concentration of auxins in the apical shoot
high concentration of auxins supress growth of lateral shoot, resulting in apical dominance
low concentration of auxins promote seed growth
experimental evidence supporting the role of auxins
if the apical shoot is removed, auxin producing cells are removed which means no auxins are present so lateral shoots will grow faster as there is no apical dominance. ‘ essentially side shoots will begin to grow’
synergism
this is when plant hormones work together
antagonism
this is when plant hormones have opposite effects
what are the main 5 plant responses to abiotic stress
- leaf loss
- daylength sensitivity
- abscission
- preventing freezing
- stomatal control
leaf loss in deciduous plants as a response to abiotic stress
trees lose their leaves in colder months, this helps conserve water as less photosynthesis is taking place
auxins act to inhibit abscission whereas ethene acts as an antagonist and promotes abscission
daylength sensitivity ( plant response to abiotic stress)
this is known as photoperiodism, this affects dormancy of leaf buds.
sensitivity of plant to day length results from a light sensitive pigment known as phytochrome.
what does phytochrome exist as
Pr and Pfr
each absorb a different type of light in the ratio pr to pfr
preventing freezing
if cells freeze, membranes are disrupted causing them to die
plants have evolved mechanisms’ to help them protect themselves, cytoplasm contain sap in the vacuole which has solutes to lower freezing point
stomatol control
response to abiotic stress
stomata opens, plant cools down as the water evaporated in transpiration
stomata closes, conserves water
what is stomatal opening and closing controlled by
Abscisic acid , ABA
binds to receptors on guard cells
this causes calcium ion channels to open
influx of calcium ions causes potassium ion channels to open
potassium ions leave guard cell
wp in the cell increases, water moves out by osmosis
guard cell is flaccid closing stomatal potr
plant physical responses to herbivory
thorns
barbs
spikes
spiny leaves
hairy leaves
stings
chemical defences
- tannins
bitter taste which can interfere with digestion - alkaloids
bitter taste and are poisonous
-terpenoids
toxic to insects
pheromones
chemical made by an organism which affects the social behaviour,
plant response
folding in response to touch
it helps to knock off or scare any insects feeding on it
PRIME EXAMPLE MIMOSA PUDICA
What is tropism
it is the plant growth response to stimuli
what are the type of tropisms
- phototropism:
response to light - geotropism:
response to gravity - chemotropism
response to chemicals - thigmotropism
response to touch
phototropism response
+ve shoots grow towards the light
-ve roots grow away from the light
geotropism response
+ve roots grow down to the soil
-ve stems grow upwards
effect of positive phototropism
maximises the amount of sunlight absorbed for photosynthesis
effect of negative phototropism
ensures that roots bury themselves deeper within the soil so that they can absorb more water for photosynthesis
effect on unilateral light
.
commercial uses of plant hormones
auxins are used in rooting powders to stimulate root growth on plant cuttings
auxins are used in herbicides which prevent sem elongation
ethene is used to control fruit ripening
cytokinins prevent ageing of ripened fruits
giberellins delay ripening and ageing in fruots
auxins can be used in production of seedless fruits
