Lecture 3 Flashcards
How do different parts of a plant signal to each other to co-ordinate plant growth and development and respond to stimuli
What is a hormone
a circulating chemical signal that co-ordinates various parts of the organism by interacting with target cells
how much of hormones are needed
act in low concentrations
What is the response governed by
usually by interaction between two hormones
What does it mean by signal transduction
links a stimulus to a response
State the general pathway of a signal
stimulus/ signal —> perception & signal transduction –> response
Where does a hormone bind
receptors
What does a hormone activate
activate a signal transduction pathway
- second messenger increase in concentration
- phosphorylation by protein kinase
- switch on or activate TF
- protein-protein interactions
What are the two common types of second messengers
Ca2+
cAMP
what is the cells response to hormones
- gene expression
- ion fluxes in the cell
- physiological responses
- developmental responses
true or false; light is a signal
true
what happens when light is shone to seedlings
they grown towards the light (positive phototropism)
When light is shone to cereal seedlings what happens
the dark side shows cell expansion as seedlings bend toward the light
What did Darwin and Darwin discover about light and seedling growth; when was it too
Darwin and Darwin discovered that light is perceived at the tip of the seedling
1880
What were the experiment performed by Darwin and Darwin (5 in total)
control (bends) cut tip (remained vertical) tip covered by opaque cover (vertical) tip covered by clear cap (bends) base covered by opaque cover (bends)
What did Darwin conclude from his experiments
signal travels from tip to base
What did Boysen and Jensen discover and when
1913
- chemical messenger moves down the stem
What were the 2 experiments that Boysen and Jensen carry out in 1913
- ) tip separated by gelatin block (bends)
2. ) tip separated by mica ( not bend)
When was it discovered that auxin was the signal
1930s
What was the Wendt experiment and when
1926
- demonstrated that chemical signal/messenger moves asymmetrically downward the stem
What is the natural occuring derivative of auxin
Indole acetic acid (IAA)
- promotes growth
What does auxein in greek mean
to increase
What did Wendt discover about the rate of IAA transport
it travels much faster basopetally
- uni directional/polar transport
(from tip to base)
- flow inhibited in acropetal direction (base to tip)
how does auxin only move in one direction in the stem?
- auxin moves into the cells across the plasma membrane
- PIN proteins located in the basal membrane of the cell transports IAA (-) out of the cell; located at the end of each xylem parenchyma cell
Overall what is the mechanism of phototropism
- ) light signal is perceived at the shoot tip
- ) induces asymmetric transport of auxin on shaded side down the through cells of stem
- ) auxin is bound by receptors
- ) cell elongation is stimulated (auxin stimulates loosening of cellulose microfibrils in the wall); (turgor pressure causes cell expansion)
- ) shoot tips bend towards the light
- ) early auxin response genes are switched on in cells, increased gene expression
what is the only naturally made auxin
IAA
- made from amino acid tryptophan
What are the 2 synthetic auxins
2,4 D
NAA
where are auxins synthesized primarily
leaf primordia
young leaves
developing seeds
What are the functions of auxin
-phototropism
-fruit growth - stimulated by auxins secreted by
seeds
- position of leaves (spiral phyllotaxy)
- apical dominance (auxin in shoot tip mediate apical dominance)
What happens when pin1 mutant of arabidopsis is injected with auxin
stimulates outgrowth of primordium in pin1 mutant
what happens when SAM is removed
lateral axillary meristems grow up and one takes over (useful survival mechanism)
what does axillary mean
meristems or buds or branches occuring in axils of a leaf
What controls the growth of the axillary meristems
the ratio of cytokinins to auxins
- the cells sense this, controls growth of the axillary meristems
true or false; another gradient is established in the root tips; established by cytokinins
true
What are the commercial uses of synthetic auxins
NAA, IBA
- rooting of cuttings
- induction of parthenocarpy in glass house tomatoes (fruit set without fertilization)
What herbicides are used for dictots
2,4, D
2,4,5 T
What is agent orange
2,4,5 T mixed with TCDD (carcinogen)
- tactic of american military during the vietnam war to reduce the vietcongs food supply
When was the role of hormones uncovered
uncovered as a chemical messenger when scientists were studying phototropism; where seedlings bend towards the light
What is auxin
a chemical messenger in phototropism where its role is in cell elongation
What is IAA
is an auxin synthesized in plants from the amino acid tryptophan mainly in leaf primordia and young leaves and developing seeds
true or false; auxin is transported by cell to cell
true
Give examples of auxin functions
regulating organ patterning
cell differentiation
apical dominance
fruit expansion
