Lecture 3

Question 1

What is a hormone

Answer 1

a circulating chemical signal that co-ordinates various parts of the organism by interacting with target cells

Question 2

how much of hormones are needed

Answer 2

act in low concentrations

Question 3

What is the response governed by

Answer 3

usually by interaction between two hormones

Question 4

What does it mean by signal transduction

Answer 4

links a stimulus to a response

Question 5

State the general pathway of a signal

Answer 5

stimulus/ signal —> perception & signal transduction –> response

Question 6

Where does a hormone bind

Answer 6

receptors

Question 7

What does a hormone activate

Answer 7

activate a signal transduction pathway

• second messenger increase in concentration
• phosphorylation by protein kinase
• switch on or activate TF
• protein-protein interactions

Question 8

What are the two common types of second messengers

Answer 8

Ca2+

cAMP

Question 9

what is the cells response to hormones

Answer 9

• gene expression
• ion fluxes in the cell
• physiological responses
• developmental responses

Question 10

true or false; light is a signal

Answer 10

true

Question 11

what happens when light is shone to seedlings

Answer 11

they grown towards the light (positive phototropism)

Question 12

When light is shone to cereal seedlings what happens

Answer 12

the dark side shows cell expansion as seedlings bend toward the light

Question 13

What did Darwin and Darwin discover about light and seedling growth; when was it too

Answer 13

Darwin and Darwin discovered that light is perceived at the tip of the seedling
1880

Question 14

What were the experiment performed by Darwin and Darwin (5 in total)

Answer 14

control (bends)
cut tip (remained vertical)
tip covered by opaque cover (vertical)
tip covered by clear cap (bends)
base covered by opaque cover (bends)

Question 15

What did Darwin conclude from his experiments

Answer 15

signal travels from tip to base

Question 16

What did Boysen and Jensen discover and when

Answer 16

1913

- chemical messenger moves down the stem

Question 17

What were the 2 experiments that Boysen and Jensen carry out in 1913

Answer 17

1. ) tip separated by gelatin block (bends)

2. ) tip separated by mica ( not bend)

Question 18

When was it discovered that auxin was the signal

Answer 18

1930s

Question 19

What was the Wendt experiment and when

Answer 19

1926

- demonstrated that chemical signal/messenger moves asymmetrically downward the stem

Question 20

What is the natural occuring derivative of auxin

Answer 20

Indole acetic acid (IAA)

- promotes growth

Question 21

What does auxein in greek mean

Answer 21

to increase

Question 22

What did Wendt discover about the rate of IAA transport

Answer 22

it travels much faster basopetally
- uni directional/polar transport
(from tip to base)
- flow inhibited in acropetal direction (base to tip)

Question 23

how does auxin only move in one direction in the stem?

Answer 23

• 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

Question 24

Overall what is the mechanism of phototropism

Answer 24

1. ) light signal is perceived at the shoot tip
2. ) induces asymmetric transport of auxin on shaded side down the through cells of stem
3. ) auxin is bound by receptors
4. ) cell elongation is stimulated (auxin stimulates loosening of cellulose microfibrils in the wall); (turgor pressure causes cell expansion)
5. ) shoot tips bend towards the light
6. ) early auxin response genes are switched on in cells, increased gene expression

Question 25

what is the only naturally made auxin

Answer 25

IAA

- made from amino acid tryptophan

Question 26

What are the 2 synthetic auxins

Answer 26

2,4 D

NAA

Question 27

where are auxins synthesized primarily

Answer 27

leaf primordia
young leaves
developing seeds

Question 28

What are the functions of auxin

Answer 28

-phototropism
-fruit growth - stimulated by auxins secreted by
seeds
- position of leaves (spiral phyllotaxy)
- apical dominance (auxin in shoot tip mediate apical dominance)

Question 29

What happens when pin1 mutant of arabidopsis is injected with auxin

Answer 29

stimulates outgrowth of primordium in pin1 mutant

Question 30

what happens when SAM is removed

Answer 30

lateral axillary meristems grow up and one takes over (useful survival mechanism)

Question 31

what does axillary mean

Answer 31

meristems or buds or branches occuring in axils of a leaf

Question 32

What controls the growth of the axillary meristems

Answer 32

the ratio of cytokinins to auxins

- the cells sense this, controls growth of the axillary meristems

Question 33

true or false; another gradient is established in the root tips; established by cytokinins

Answer 33

true

Question 34

What are the commercial uses of synthetic auxins

Answer 34

NAA, IBA

• rooting of cuttings
• induction of parthenocarpy in glass house tomatoes (fruit set without fertilization)

Question 35

What herbicides are used for dictots

Answer 35

2,4, D

2,4,5 T

Question 36

What is agent orange

Answer 36

2,4,5 T mixed with TCDD (carcinogen)

- tactic of american military during the vietnam war to reduce the vietcongs food supply

Question 37

When was the role of hormones uncovered

Answer 37

uncovered as a chemical messenger when scientists were studying phototropism; where seedlings bend towards the light

Question 38

What is auxin

Answer 38

a chemical messenger in phototropism where its role is in cell elongation

Question 39

What is IAA

Answer 39

is an auxin synthesized in plants from the amino acid tryptophan mainly in leaf primordia and young leaves and developing seeds

Question 40

true or false; auxin is transported by cell to cell

Answer 40

true

Question 41

Give examples of auxin functions

Answer 41

regulating organ patterning
cell differentiation
apical dominance
fruit expansion