16.1 Plant hormones Flashcards
what is a tropism?
a response to a stimulus
what is auxin used for?
controlling cell elongation
preventing leaf fall
maintaining apical dominance
stimulating ethene release
fruit ripening
what is gibberellin used for?
causes stem elongation
stimulates pollen tube growth
seed germination
lateral shoot growth
how is the relationship between auxin and gibberellin synergistic?
they work together to make a plant tall
how is the relationship between auxin and gibberellin antagonistic?
gibberellin stimulates lateral shoots growth while auxin inhibits it
what is ethene used for?
causes fruit ripening
promotes abscission
what is ABA used for?
maintain seed dormancy
stomatal closing control
anti-freeze measures
it inhibits gibberellin
how are gibberelins involved in seed germination?
when seed absorbs water, embryo is activated and gibberellins are produced
gibberellins stimulate production of enzymes which break down food stores
the plant uses food stores to produce ATP to grow
gibberellins also switch on genes which code for amylases and proteases which are required for seed germination
what evidence supports gibberelins being involved in seed germination?
mutant seeds which lack the gene allowing for gibberellin production did not germinate but when gibberellins were added externally they germinated
if gibberellin inhibitors are added to a plant they don’t germinate but once removed they germinate
what inhibits Gibberellins?
ABA
where is auxin produced?
in the tips of the roots and shoots
meristems
what are the 3 main effects of auxin in plant growth?
stimulate growth of the apical shoot
high concentrations suppress the growth of lateral shoots
low concentrations in the root promote root growth
what evidence is there to show that auxins stimulate shoot growth?
presence of auxin makes the cell wall stretch more easily
auxin binds to receptor sites in the cell surface membrane causing the pH to fall to an optimum pH level to keep the walls flexible and plastic
once plant matures, auxin is destroyed and the wall becomes rigid
what causes the plant membranes to be plasticy or rigid?
enzymes
hence their activity is controlled by pH which is controlled by Auxin
what is apical dominance?
when the central vertical shoot grows dominantly over the lateral branches
how does auxin cause apical dominance?
auxin is in high concentration at the apical bud
this is where the most inhibition of lateral growth occurs
as you go down the plant, auxin concentration decreases
so less inhibition of lateral growth
so more growth of lateral shoots
what evidence is there to show auxin suppressing the growth if lateral shoots?
if the apical shoot is removed, the lateral shoots grow faster as there is no auxin to inhibit their growth
BUT
if auxin is reapplied externally growth is stopped
how do auxin concentrations increase root growth?
low auxin concentration in the roots means more root growth
how do auxin concentrations decrease root growth?
high auxin concentration in the roots inhibits growth of roots
how do gibberellins affect elongation?
they affect the length of the internodes between the leaves on a stem
what evidence shows the affect of gibberellins on stem elongation?
if gibberellin action is interrupted the plant is much shorter
length of internodes decreases
DWARF PLANTS
what is synergism?
when hormones compliment eachother
what is antagonism?
when hormones inhibit eachother
