Lecture 26: Plant Hormones

Question 1

etiolation

Answer 1

morphological adaptations for growing in darkness

Question 2

detiolation

Answer 2

• happens after exposure to light, shoots and roots grow normally

Question 3

A potato’s response to light is an example of

Answer 3

cell-signal processing

Question 4

stages of cell signal processing

Answer 4

1. reception
2. transduction
3. response

Question 5

What are plant hormones important for

Answer 5

coordinating growth, development, and stimuli responses

Question 6

what are plant hormones

Answer 6

chemical signals that modify/control more specific physiological processes within a plant

Question 7

5 main plant hormones

Answer 7

1. auxin
2. cytokinin
3. gibberellins
4. abscisic acid
5. ethylene

Question 8

Plant hormones are produced in a _____ concentration

Answer 8

very low

Question 9

Hormones control plant growth

Answer 9

affect division, elongation, and differentiation of cells

Question 10

a response resulting in curvature of organs toward or away from a stimulus is

Answer 10

a tropism; growth toward a stimulus

Question 11

what is the chemical messenger for phototropism

Answer 11

auxin

Question 12

Auxin

Answer 12

• any chemical that promotes elongation of coleoptiles
• specifically indoleacetic acid (IAA) type of auxin

Question 13

explain auxin and proton pumps

Answer 13

1. auxin stimulates proton pumps in the plasma membrane
2. proton pumps lower pH in cell wall, activating expansins
3. expansins loosen wall’s fabric and allow cell to expand

Question 14

what does reduced auxin flow from the shoot of a branch do?

Answer 14

it stimulates growth in lower branches

Question 15

auxin transport plays a role in ______, arrangement of leaves on the stem

Answer 15

phyllotaxy

Question 16

auxin also controls what 2 functions

Answer 16

• leaf venation pattern, activity of vascular cambium
• more auxin, more cell elongation

Question 17

auxin indolbutryic acid (IBA)

Answer 17

stimulates adventitious roots

Question 18

Cytokinins main purpose

Answer 18

stimulate cell division

Question 19

How are cytokinins produced

Answer 19

in actively growing tissues such as roots, embryos, and fruits

Question 20

cytokinins and work _____ together to do what

Answer 20

auxins; control cell division & differentiation

Question 21

what 3 hormones control apical dominance

Answer 21

auxin, cytokinins, strigolactone

Question 22

what happens to a plant if the terminal bud is removed

Answer 22

plants become bushier

Question 23

Gibberellins

Answer 23

• affect stem elongation, fruit growth, and germination
• produced in young roots, leaves, & stems
• stimulate **growth of leaves & stems **via cell elongation & division

Question 24

in plants, what 2 hormones must be present for fruit to develop

Answer 24

auxin & gibberellins

Question 25

Release of gibberellins from the embryo causes

Answer 25

- signals seeds to germinate - endosperm breaks down

Question 26

Abscisic Acid

Answer 26

- important in **seed dormancy**; ensures seed germinates only in optimal conditions - takes a strong ext. factor like heavy rain to break dormancy - ABA is the **primary internal signal** enabling plants to withstand drought - ABA causes stomata to **close rapidly**

Question 27

Ethylene

Answer 27

- "emergency response" - plants produce it in response to stresses like drought, flooding, mechanical pressure, infection

Question 28

4 main responses of ethylene

Answer 28

1. mechanical stress 2. senescence 3. leaf abscission 4. fruit ripening

Question 29

mechanical stress

Answer 29

- "triple response" - stem elongation, thickening, horizontal growth

Question 30

Senescence

Answer 30

programmed death of cells or organs

Question 31

a burst of ethylene is associated with ____, the programmed desruction of cells, organs, whole plants

Answer 31

apoptosis

Question 32

steps of cell death

Answer 32

- ethylene --> apoptosis --> senescence --> death

Question 33

Leaf Abscission

Answer 33

- process that occurs in autumn when a leaf falls - auxin & ethylene imbalance