Plant Responses to the Environment - Flowering/Tropisms

Question 1

how are SHADE and the NIGHT different (2)

Answer 1

• shade: presence of red and far red photons; fast phytochrome response
• night: absence of red and far red photons; slow phytochrome response

Question 2

how do plants measure seasons (2)

Answer 2

• measure night length using the phytochrome system

- most reliable indicator of the season

Question 3

why do plants measure the time of year (4)

Answer 3

to schedule complex physiological changes:

• flowering
• when to produce storage organs
• programmed senescence
• when to begin dormancy

Question 4

what are the two ways to change Pfr:Pr ratio

Answer 4

• conformational changes in response to light: fast process that regulates germinations
• night reversion: slow process that regulated flowering

Question 5

how do plants measure the length of the night (2)

Answer 5

• during the night (absence of light), Pfr reverts SLOWLY (hours) to Pr, causing the Pfr:Pr ratio to decrease as the night progresses
• lower Pfr:Pr ratio detected at sunrise indicates longer period of darkness/longer night

Question 6

short night plants (2)

Answer 6

• require high Pfr:Pr ratio at sunrise to flower

- likely flower in the summer

Question 7

long night plants (2)

Answer 7

• require low Pfr:Pr ratio at sunrise to flower

- likely flower in the spring

Question 8

can Pfr:Pr ratio be altered synthetically to change flowering regulation (2)

Answer 8

yes, through light flashes in the night that is expressed for many nights

• red flash will produce higher Pfr:Pr ratio, resembling a shorter night
• far red flash will produce lower Pfr:Pr ratio, resembling a longer night

Question 9

auxin

Answer 9

• plant growth hormone

Question 10

plant phototropism to blue light

Answer 10

• tendency of plants to bend toward blue light

Question 11

what are the main functions of auxin (3)

Answer 11

• drive plant responses to light (phototropism)
• drive plant responses go gravity (gravitropism)
• regulate cell elongation

Question 12

how do shoots detect blue-light (3)

Answer 12

• PHOT1 is the blue-light receptor
• PHOT1 phosphorylates itself in response to blue light
• once this receptor is phosphorylated, a phototropic response is initiated

Question 13

where is the blue-light sensor located?

Answer 13

• blue light is sensed by the coleoptile tip of the shoot in order to trigger the phototropic response

Question 14

how does bending of shoots occur in response to blue light (3)

Answer 14

• there must a signal that travels from the tip to the base of the stem
• signal must be a chemical that diffuses through the plant shoot
• the diffusible hormone is able to promote bending by itself in the absence of light

Question 15

the acid-growth hypothesis

Answer 15

• acid growth refers to ability of plant cells to loosen cell walls an expand quickly at low (acidic) pH

Question 16

what will the turgor pressure be in a plant with an expansin knock out mutation (2)

Answer 16

• after turgor pressure increase, it will remain unchanging

- as the cell does not grow, volume of the cell remains the same, and the pressure is not released

Question 17

gravitropic response (2)

Answer 17

• tendency of roots to grow towards the gravity vector

- tendency of shoots to grow against the gravity vector

Question 18

gravity sensor of the roots (2)

Answer 18

• roots have protective cap with gravity-sensing/columella cells at the centre of the cap
• laser removal of these cells will destroy the gravitropic response in roots

Question 19

how do columella cells detect gravity (3)

Answer 19

• cells are filled with dense amyloplasts that sink under the force of gravity
• sedimentation of the amyloplasts activate pressure receptors
• if roots are reoriented under gravity, the amyloplasts will start sedimenting to the new bottom surface

Question 20

what affects the auxin mechanism of action (2)

Answer 20

• can stimulate or inhibit growth, depending the concentration of the auxin and the specific tissue it is acting on
• same concentration of auxins can promote and inhibit in different plant parts

Question 21

if a plant root is tipped over, how does the bottom of the root differ from the top of the root (2)

Answer 21

• inhibits growth

- higher concentration of auxin

Question 22

how does the side of the plant that is not facing blue light, differ from the side that is (2)

Answer 22

• higher auxin concentration

- experiences more growth