Plant responses chp 16 Flashcards
what are some general functions of auxins within plants
- control cell elongation
- prevent abscission (leaf fall)
- maintain apical dominance
- important for tropisms
- stimulates the release of ethene
what are some functions of gibberellins
- causes stem elongation
- triggers mobilisation of food stores in seed at germination
- stimulate pollen tube growth in fertilisation
what are some functions of ethene
- causes fruit ripening
- promotes abscission
what are some functions of ABA, what does ABA stand for
abscisic acid
- maintains dormancy of seeds and buds
- stimulates cold protective responses (antifreeze production)
- stimulates stomatal closing
What occurs when a seed germinates
seed absorb water
embryo is activated and starts producing gibberellins
^stimulates production of amylase and protease that breakdown food stores
plant uses to produce ATP for metabolic activites
what is some evidence that supports the role of gibberellins in the germination of seeds
- if mutant seeds do not produce gibberlins they do not germinate but once given do germinate
- if gibberelin inhibitors are applied to seeds do not germinate if taken off they do germinate
where can auxins be mainly found In the plants
inthe cells at the tip of roots, shoots and in meristem
explain effect of auxins on plant cell walls
- effect elasticity of cell walls - more auxins means stretches more easily
- stimulates fall in pH, optimum for enzymes that maintain elasticity
- as cell mature auxins destroyed, pH rises again so elasticity is removed from the cell wall and become rigid
what are the 3 zones that can be found in the apical shoot
explain effect of auxin on lateral shoots
- high concentrations of auxins suppress lateral shoots
- ^results in apical dominance
- further down stem auxin concentration is lower and so lateral shoots grow
- if you removed apical shoot lateral grow starts
- ^if you artificially replace it with auxins apical dominance is reasserted
explain how auxins effect root growth
- low concentrations of auxins promote root growth
- more auxin that reaches the roots the more they grow (up to a point)
- if apical shoot is removed then amount of auxin reaching roots is reduced and root growth slows
Explain how gibberellins effect stem length
- influences length of the internodes - the region between the leaves on a stem
what is meant by antagonism when talking about hormones
substances have opposite effects, e.g promoting and inhibiting growth
what is photoperiodism
the response to changes in daylength that enables plants to adapt to seasonal changes in their environment
what allows plants to be sensitive to day length/dark length
results from light-sensitive pigment called phytochrome
How does leaf abscission actually work
- abscission zone (base of leaf stalk) made up of protective and seperation layer
- Ethene initiates production of enzyme (turn genes on/off)
- enzymes digest cell walls of abscission zone
- vascular bundles going to and from stalk sealed off
- fatty material deposited in cells at abscission zone
^scar, prevents pathogens entering - cells in separation zone retain water and swell putting strain on outer layers
- abiotic factors help leaves fall
how do plants prevent damage from freezing
- cytoplasm of cells and sap contain solutes which lower freezing point - such as sugars, amino acids & proteins
controlled by gene experession
How do the lengths of days actually cause abscission
- falling light levels causes auxin concentration to fall
- plants produce ethene in response to less auxin
- abscission zone is sensative to ethene (begins breaking down)
what hormone influences stomatal opening and closing and how does it do it
- ABA
- binds to receptors on cell membranes of guard cells
- activates changes in ionic concentrations of guard cells,
^reduces water potential and therefore turgor - ^as result of less turgor, guard cells close the stomata
- water loss Is reduced
what are some commons plant physical defences
- throws, bards, spikes, spiny leaves, fibrous and inedible tissue and stings
what are some common plant chemical defences
- tannins
- alkaloids
- terpenoids
- pheromones
how do alkaloids acts as plant defences
- very bitter tasting
- act as drugs that affect metabolism of animals
- caffeine, morphine, nicotine, cocaine
how do phermones act as plant defences
- chemical made by organism which affects behaviour of same species
- can alert others of things like insects or water stress
How do VOC’s link to phermones and how do they act as plant defences
- act like pheromones but effect the behaviour of other animals
- diffuse in the air around plants
- cabbages release VOC’s after being attacked by caterpillars
- VOC’s attract wasps that lay eggs inside of the caterpillars, killing them
