16.1 Plant hormones and growth in plants Flashcards
what roles do auxins have in plants (4)
- cell elongation
- prevent abscission
- maintain apical dominance
- stimulate ethene release
what roles do gibberellins have in plants (3)
- stem elongation
- seed germination
-stimulate pollen tube growth at fertilisation
what roles do ethene have in plants (2)
- promote fruit ripening
- promotes abscission
what roles does abscisic acid (ABA) have in plants (3)
- stimulates stomatal closure
- maintains seed and bud dormancy
- stimulates cold protective responses
what is synergism (of hormones)?
interactions between two hormones which have similar effects to give a greater response
what is antagonism (of hormones)?
interactions between hormones which have opposite effects and overall effect depends on balance of hormones
what is a tropism
a directional growth response by a plant in response to a unidirectional stimulus
outline the process of germination
- Seed absorbs water, produces gibberellins.
- Gibberellins stimulate production of enzymes, hydrolysing food stores.
- Glucose from food stores used to produce ATP by aerobic respiration.
- ATP used to produce building materials for growth.
what plant hormone is antagonistic to gibberellins
abscisic acid (gibberellins promote germination ABA maintains dormancy)
how can dwarf species of plants be made
by interrupting the pathway of gibberellin production
what can grafting 2 dwarf plants together do
(if the 2 plants lack a different step in the gibberellin production pathway…)
Grafting will complete the pathway,
gibberellins can be produced,
leading to growth of internodes/stem.
what experimental evidence is there for the role of gibberellins in germination
-Mutated varieties of seeds, which do not contain the gibberellin gene, do not germinate.
-Applying gibberellin biosynthesis inhibitors prevents germination.
(in both experiments, adding gibberellins externally leads to germination)
in what three ways does auxin influence plant growth
-stimulates growth of apical shoot
-inhibits growth of lateral buds
-stimulate root growth @ low concentrations
what is apical dominance
where the growth of the central stem of a plant is dominant over the growth of lateral stems
outline the mechanism by which auxins cause growth of the apical shoot
1.Auxin molecules bind to specific, complementary receptors on plasma membrane
2.Decreases pH, which increases cell wall flexibility. (optimum pH for enzymes responsible for keeping cell walls flexible)
3.Allows cell to absorb more water by osmosis & expand
4.As cells mature, auxin destroyed, pH rises, cell wall becomes rigid.
- No further growth
