plant hormones Flashcards
What is IAA made by?
- made by cells in the apical meristem tissue in roots and shoots
What is apical dominance?
- IAA is made by apical meristem and travels throughout the plant via diffusion
- a high concentration of IAA in lateral bud inhibits its growth
What are the antagonistic hormone for IAA?
- cytokinin
- abscisic acid
What does cytokinin do?
- it promotes the growth of lateral buds
Describe the process of positive phototropism?
- if the stem is exposed to unidirectional light, the IAA made by the apical meristem will travel down the plant by diffusion and concentrate itself on the shaded side
- in the stem, IAA promotes cell elongation so the cells on the shaded side elongate and the plant grows towards the light for maximum photosynthesis
Describe the process of geotropism/ gravitropism in roots?
- the stimulus is gravity
- place seeds in a klinostat apparatus and spin so all side of the seed is exposed to gravity
- when you then stop the machine, only once side is exposed to gravity
- IAA concentrated on the lower side of the seed due to gravity
- in roots, IAA inhibits cell elongation
- where there is a lower concentration of IAA, there is more cell elongation so root grows towards gravity
define tropism?
- directional growth in response to a stimulus
how can hormones move through the plant?
- from cell to cell
- or through transport tissue
How does auxin cause cell elongation?
- IAA binds to the complementary receptors on plant cells
- this causes H+ ions to be pumped from the cytoplasm into the cell wall, lowering the pH
- this is a suitable temperature for the enzyme cellulase and pectinase
- IAA causes water to move in via osmosis
- plant becomes turgid but because the cell wall’s plasticity has increased, the cell elongates
why do lateral branches grow more further down the plant?
- the concentration of auxin is lower
what is the hormone gibberellin involved in?
- seed germination
- elongation of plant stems during growth
In what part of the stem does gibberellin act on?
- internodes which is the space between two lateral branches
Why are some plants shorter(dwarf)?
- they have a lack of active, functioning gibberellin acid
- if the enzyme that converts GA20 to GA1(which is the active form of GA) is absent, then the plants are genetically short
Which gene codes for the enzyme which converts inactive precursor GA20 into an active functional form of GA1
- Le.. the dominant allele codes for the enzyme
- if the gene is in recess form, it will code for non-functional GA because it can’t code for the enzyme
How does GA promote seed germination?
- seeds uptake water inside via the pore
- this allows the embryo to produce GA
- GA from the embryo diffuses to the aleurone layer where there are cells that produce hydrolase enzymes
- GA promotes transcription of the genes that code for the hydrolase enzymes
- stored food in the seed like starch, triglycerides and protein are hydrolysed
- this is absorbed by the embryo and it can now grow into a new plant
