Ch. 39 Plant Responses

Question 1

what is etiolation?

Answer 1

the responses of a plant to growing in darkness

Question 2

what is de-etioliation?

Answer 2

the series of changes a plant previously in dark undergoes when being exposed to the sun

Question 3

what are the 3 steps of cell signal transduction?

Answer 3

-reception, transduction, and response

Question 4

what are the steps of the 2nd messenger cGMP cascade?

Answer 4

1. cGMP activates protein kinases / PKs
2. PKs activate transcription factors (TFs)
3. TFs turn on genes for transcription
4. transcribed genes get turned into response proteins

Question 5

what is the 1st step of a plant cell’s signal transduction pathway?

Answer 5

1st step begins when a stimulus (ex - light) binds to a receptor, such as phytochrome

Question 6

what is phototropism?

Answer 6

growth of a plant in response to light. can be towards (+) or away from (-)

Question 7

what is the major function of auxin?

Answer 7

responsible for tropism of plants - phototropism and gravitropism

Question 8

how does auxin result in phototropism?

Answer 8

auxin moves to the opposite side of the light source of the plant, causing elongation in the opposite side which results in the plant “bending” towards the source

Question 9

how is auxin transported? [what is polar transport]?

Answer 9

auxin moves unidirectionally: always from shoot tip downwards, and is transported through cells via diffusion by active transport

Question 10

what does auxin stimulate cells to do?

Answer 10

auxin stimulates shady cells to pump H+ out of the cell into the cell wall

Question 11

what is the acid growth hypothesis?

Answer 11

a hypothesis that auxins causing cells to pump H+ out of the cell, and therefore activating enzymes such as expansin, results in enlargement of the cell

Question 11

what does auxin do to the inside of a cell, after H+ has been pumped out?

Answer 11

-increase in charge difference stimulates cations to enter the cell
-this decreases Ψs = water moves into cell = increase in turgor pressure

Question 12

what is photomorphogenesis?

Answer 12

changes in morphology/shape due to light intensity/wavelength/availability

Question 13

what plant processes does blue light regulate?

Answer 13

phototropism, stomata opening/closing, and slowing of growth of seedlings out of soil

Question 14

what blue light photoreceptor is responsible for phototropism?

Answer 14

phototropin

Question 15

what blue light receptor controls the opening of stomata?

Answer 15

zeaxanthin

Question 16

what blue light photoreceptor controls the growth of seedlings as they break the soil surface?

Answer 16

cryptochromes

Question 17

what is a phytochrome?

Answer 17

a pigment with 2 different forms that responds to two types of light

Question 18

what two forms of light do phytochromes respond to?

Answer 18

red light (Pr) and far-red light (Pfr)

Question 19

what do phytochromes do when stimulated by red light and far-red light?

Answer 19

-red light (660nm) stimulates a switch from the inactive Pr to the active Pfd
-far-red light (730nm) stimulates a switch from the active Pfr to the inactive Pr

Question 20

what is the function of Pfr?

Answer 20

to stimulate germination and flowering in plants, as well as stimulating flowering in long-day plants

Question 21

what is the function of Pr?

Answer 21

to inhibit germination + flowering in plants, as well as inhibiting flowering in long-day plants

Question 22

how do different flashes of red and far-red light affect a plant?

Answer 22

-only the last flash of light (red or far red) determines what will happen, all flashes before are invalidated

Question 23

what are long-day / short-night plants?

Answer 23

plants that flower when the nights are shorter than a given critical period: lettuce, spinach, spring-blooming flowers

Question 23

what is photoperiodism?

Answer 23

a physiological response of a plant with respect to the length of night

Question 24

what are short-day / long-night plants?

Answer 24

-plants that flower when nights are longer than a certain critical period: soybeans, poinsettias, asters, fall-blooming flowers

Question 25

what wavelengths of light are involved in regulating plant flowering?

Answer 25

red light / far-red light

Question 25

what are day-neutral plants?

Answer 25

plants who flower regardless of day length, such as tomatoes

Question 26

what is gravitropism?

Answer 26

the growth of plants in response to the force of gravity. can be with gravity (+, roots) or against gravity (-, shoots)

Question 27

what are statoliths?

Answer 27

microscopic “rocks” in a plant that settle on their root downside, allowing them to sense gravity

Question 28

what is thigmomorphogenesis?

Answer 28

changes in plant form / growth due to environmental disturbances

Question 29

what is thigmotropism?

Answer 29

directional growth by plants in response to touch - ex - pea tendrils

Question 30

what are “rapid leaf movements” with regards to thigmotropism?

Answer 30

acute, immediate responses by a plant to touch, such as a venus fly trap snapping shut when touched by a fly

Question 31

what are pulvini cells and what is their function?

Answer 31

pulvini = specialized “motor organs” within a plant that can sense touch

Question 32

what happens in a plant when pulvini cells sense touch?

Answer 32

-K+ leaves = Ψs increases = water leaves = leaves shrivel up and allow for desired movement