5.5.2 controlling plant growth Flashcards
apical dominance
inhibition of lateral buds further down shoot by chemicals produced by apical bud at tip of plant shoot
auxins
plant hormones which are responsible for regulating plant growth
gibberellins
plant hormones responsible for control of stem elongation & seed germination
(auxins) what happens if you break the shoot tip off a plant
plant starts to grow side branches from lateral buds that were previously dormant
apex
shoot tip
what was suggested about auxins from the apical bud
prevent lateral buds growing
- how did researchers test their hypothesis that the auxins from apical buds stop lateral buds growing?
- what are the issues with this?
- how did researchers deal with these issues?
applied paste containing auxins to cut end of shoot = lateral buds didn’t grow
issues:
- manipulation of plants could have unexpected effect
- upon exposure, cells in cut end of stem could have produced hormone that promoted lateral growth
solution:
- applied ring of auxin transport inhibitor below apex of shoot & lateral buds grew
what did scientists suggest about auxin levels
normal = inhibit growth
low = promote growth
why is it suggested that 2 other hormones are involved in lateral bud growth
a scientist found auxin levels in lateral buds of kidney beans increased when shoot tip cut off
(auxins) two other hormones potentially involved & how?
- abscisic acid = inhibits bud growth
- high auxin in root may keep abscisic acid levels high in bud
- when tip (source of auxin) removed = acid levels drop & bud starts to grow - cytokinins = promote bud growth
- directly applying can override apical dominance effect
- high levels of auxin = shoot apex becomes sink for cytokinins produced in roots
- apex removed = cytokinin spreads evenly around plant
what 2 processes are gibberellins involved in
- stem elongation
- seed germination
