Plant Responses to the Environment - Light

Question 1

what triggers plant stress responses (list some) (6)

Answer 1

environmental variability:

• light intensity/spectral quality
• water potential/nutrients
• temperature
• day-length
• herbivores/pathogens
• distinguishing up from down

Question 2

what triggers plant stress responses (list some) (6)

Answer 2

environmental variability:

• light intensity/spectral quality
• water potential/nutrients
• temperature
• day-length
• herbivores/pathogens
• distinguishing up from down

Question 3

PAR

Answer 3

• photosynthesis active radiation

Question 4

plant responses: daily variability (2)

Answer 4

• sense PAR daily cycles (day/night) and day to day variability
• responds by regulating relatively SIMPLE physiological processes, such as stomatal opening

Question 5

plant responses: seasonal variability

Answer 5

• plant senses difference in the average PAR between seasons
• plants responds by regulating COMPLEX developmental programs, such as seed germination, flowering, fruit development, senescence, etc

Question 6

what are some environmental variations that plants detect when responding to daily and seasonal variability (4)

Answer 6

• light/PAR
• temperature
• rainfall
• nutrients

Question 7

sensing mechanisms at the cellular level: plants vs animals (2)

Answer 7

• have similar sensing mechanisms/fundamental components at the cellular level
• main difference is the stimulus that triggers the physiological/cellular response

Question 8

what is the general response to this stimulus: gravity

Answer 8

• cells on opposite side of root or shoot elongate; tissue curves

Question 9

what is the general response to this stimulus: touch/wind

Answer 9

• stems grow shorter and thicker

Question 10

what is the general response to this stimulus: touch (venus fly trap)

Answer 10

• target cells swell and trap shuts

Question 11

what is the general response to this stimulus: pathogens

Answer 11

• hypersensitive response where infected cells die

Question 12

what is the general response to this stimulus: herbivores

Answer 12

• insecticide production

Question 13

relationship between: stomatal opening, transpiration, and light intensity (3)

Answer 13

• increase in light intensity:
• stomatal openings increase
• plant transpiration, how much water is lost through the stomata, increases

Question 14

how do plants respond to blue/red light (2)

Answer 14

• activates photosynthetic antenna and induces ATP and NADPH synthesis
• facilitates CO2 capture by promoting stomatal opening

Question 15

which light beams are best at promoting stomatal opening (3)

Answer 15

• only red light is the weakest
• only blue light is intermediate
• both red and blue light is the strongest

Question 16

blue light receptors (2)

Answer 16

• sensed by phototropins PHOT1 and PHOT2 receptors, which are protein kinases
• PHOT1/PHOT2 are activated by interactions with a chromophore (a light absorbing molecule)

Question 17

how does the blue light signalling pathway trigger stomatal opening: absence of blue light (2)

Answer 17

• PHOT1 domains bind non-covalently (weakly) to the FMN chromophore
• no autophosphorylation, no signal amplification, stoma closed

Question 18

how does the blue light signalling pathway trigger stomatal opening: presence of blue light

Answer 18

• PHOT1 domains bind covalently (strongly) to the FMN chromophore
• autophosphorylation, signal amplification, stoma open

Question 19

what results from the auto-phosphorylation of PHOT1/2

Answer 19

• the photoreceptors change their activity and activate signal transduction

Question 20

is K+ essential for plants (2)

Answer 20

• K+ is an essential osmotic regulator in stomata

- is a common additive in fertilizers as it is often a limiting factor in soils

Question 21

where do seeds “prefer” to germinate

Answer 21

• in the sun: high C fixation, so seedling is well-fed

Question 22

where do seeds not “prefer” to germinate (2)

Answer 22

• in the shade: low C fixation, so seedling is starving

- seed will still germinate with water, but this is not preferred as there is limited production of biomass

Question 23

sunlight spectrum light richness (2)

Answer 23

• sunlight is rich in red light and poor in far red light

- in the sun, plants will receive more red photons than far red photons

Question 24

how would you describe the effects of red and far red light on germination

Answer 24

• antagonistic effects on germination

Question 25

how can plants sense shade (3)

Answer 25

• far red light is poorly absorbed by chlorophyll a
• red light is strongly absorbed by chlorophyll a
• as a results, seeds can sense the FR:R ratio they receive through a single phytochrome receptor

Question 26

what kind of FR:R ratio will shade have and its results

Answer 26

• high FR:R ratio

- dormancy of seeds; low germination

Question 27

what kind of FR:R ratio will sun have and its results

Answer 27

• low ratio of FR:R light

- metabolism activation in the seeds; germination

Question 28

phytochrome (2)

Answer 28

• a single receptor that moves between two conformations, depending on the predominant light wavelength (FR or R)
• changes between conformations VERY FAST

Question 29

phytochrome conformations (2)

Answer 29

• changes to Pfr after absorbing red light

- changes to Pr after absorbing far red light

Question 30

what is the active form of the phytochrome

Answer 30

• Pfr is the active form that will trigger germination

Question 31

if there are consecutive flashes of different wavelengths (FR vs R), which will determine seed germination

Answer 31

• the wavelength of the last flash will determine seed germination

Question 32

how are SHADE and the NIGHT different (2)

Answer 32

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