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Plant Phys > Signals from Sunlight and Tropism - 13 > Flashcards

Signals from Sunlight and Tropism - 13 Flashcards

1
Q

What 3 categories make up photoreceptors

A
  1. phytochromes
  2. cryptochromes
  3. phototropins
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2
Q

Define photoreceptors

A

receptor molecules that plants use to detect sunlight

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3
Q

What is the function of photoreceptors

A

they absorb photons of a given wavelength and use that energy as a signal to initiate a photoresponse

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4
Q

What do photoreceptors consist of

A

consist of a protein and a light absorbing pigment molecule called a chromophore

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5
Q

What photoreceptors are the most important

A

ones that absorb red and blue light

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6
Q

Define phytochromes

A

photoreceptors that absorb red and far-red light most strongly, but also blue and UVA radiation

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7
Q

What 3 main classes of photoreceptors mediate the effects of UV-A/blue light

A
  1. cryptochromes
  2. phototropins
  3. ZEITLUPE
    (all use flavin molecules as chromophores)
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8
Q

What are action spectrum used to determine

A

they determine which wavelengths of light are necessary to bring a particular plant response

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9
Q

action spectrum are commonly compared to what

A

absorption spectrums because they show all the light absorbed while the action spectrum shows the light actually used to emit a response

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10
Q

What kind of light is seed germination stimulated by and is inhibited by

A

stimulated by red light and inhibited by far-red light

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11
Q

The action spectrum for blue light stimulates what responses and has what kind of peak characteristic

A

phototropism, stomal movements
three finger shape

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12
Q

what absorption spectrum is almost identical to the action spectrum of phototropism (orientation of plant in response to light)

A

phototropin

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13
Q

explain how phytochrome is photoreversible

A

phytochrome can exist in two forms and can be changed from one form to another by the influence of light and is responsible for both red and far-red activities

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14
Q

What does phytochrome interconvert between

A

Pr (inactive form using far-red light)
Pfr (active form using red light)

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15
Q

How can phytochrome be degraded

A

after photoconversion occurs into active form Pfr, it can be degraded by the ubiquitin pathway (molecules broken down into smaller molecules)

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16
Q

Explain what causes Pfr to slowly or rapidly convert back to Pr

A

slowly in the darkness
or rapidly converted back due to far-red light

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17
Q

where is red light abundant and where is far-red light abundant

A

red = direct sunlight
far-red = foliage canopies

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18
Q

What is the R:FR ratio and what is it used for

A

the ratio of red to far-red light that are used for plants growing under a canopy to regulate seed germination processes and shade avoidance
the ratio decreases as the canopy increases because of less red light

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19
Q

What are some examples of typical photoreversible responses that are induced by phytochrome

A

in a seed it promotes germination, in an etiolated seedling it promotes leaf unrolling

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20
Q

Explain how long red-light induced events are reversible for

A

can be reversible by removing pfr… for a limited period of time after which they reach a point of no return and proceeds irreversibly

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21
Q

What are the functions of phytochrome (A)

A

mediates responses to continuous far-red light, change membrane potentials, and regulate gene expression

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22
Q

what does phytochrome-induced photomorphogenesis involve

A

protein degradation

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23
Q

Define cryptochromes

A

photoreceptors that interact with phytochromes to regulate photomorphogenesis (light-mediated development)

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24
Q

What functions are phototropins involved in

A

light-dependent processes that optimize photosynthetic efficiency (directing organs, chloroplast, and nuclear movements, solar-tracking, and stomatal opening)

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25
Q

What is the function of ZEITLUPE

A

participates in control of circadian clocks and flowering

26
Q

Explain the chloroplast distribution patterns in response to low, high, or darkness light

A

low light the chloroplasts have accumulation response directly in the lights path, in high light the chloroplasts have avoidance response on the outside, and in darkness they gather under the vacuole in dark position

27
Q

how does blue-light responses differ compared to normal light responses

A

they have a lag time after irradiation, and the effect of the response declines gradually after the disappearance of the light signal
whereas with normal light, the response turns on as soon as light is present and stops as soon as light goes off

28
Q

Define UVR8

A

the photoreceptor that is involved in responding to UV-B irradiation that lacks a prosthetic chromophore

29
Q

What is the function of UVR8

A

it mediates photomorphogenic processes by regulating transcription of UVR8-induced genes

30
Q

What 3 abiotic factors influence the initial growth habits of young plants during seedling establishment

A

gravity, touch, and light influence

31
Q

Define tropisms

A

directional growth responses of plants in response to particular external stimuli caused by the asymmetric growth (turning/rotating) of the stem and roots

32
Q

Explain how can tropisms be positive or negative

A

positive = growth towards the stimulus
negative = growth away from the stimulus

33
Q

Define gravitropism

A

plant growth in response to gravity

34
Q

What does gravitropism allow in plants

A

roots grow downward for water and nutrients
shoots grow upward toward sunlight for photosynthesis

35
Q

Define phototropism

A

change in plant growth patterns in response to the direction of incident radiation, especially blue-light

36
Q

What does phototropism allow

A

shoots to grow toward sunlight maximizing photosynthesis while roots grow away from sunlight

37
Q

Define thigmotropism

A

differential plant growth in response to touch (turning and bending in response to touch stimulus)

38
Q

What does thigmotropism allow/enable

A

enables roots to grow around roots and shoots to wrap around support structures

39
Q

What is the Cholodny-Went Hypothesis

A

mechanism proposed for tropisms that involves the stimulation of the bending of the plant axis due to lateral transport of auxin in response to a stimulus

40
Q

auxin transport is ____ and independent of ____

A

polar
gravity

41
Q

Explain when auxin moves basipetally and when it moves acropetally

A

basipetally = to the root-shoot junction (down from shoot, up from roots)
acropetally = from the root-shoot junction (up to shoot, down to roots)

42
Q

What facilitates gravitropism in coleoptiles

A

lateral redistribution of auxin in coleoptile tips

43
Q

Define statoliths

A

dense amyloplasts that synthesize and store starch involved in the perception of gravity contained in the root cap

44
Q

What are the 2 secondary messengers for signaling that occurs during gravitropism

A

pH and calcium ions

45
Q

Explain what occurs with auxin in gravitropic bending

A

auxin from the root tip is redirected to the lower side of the root inhibits cell elongation causing the root to bend downward

46
Q

Explain what occurs with auxin in phototropic bending

A

auxin for the shoot tip is redirected to the shaded side and stimulates cell elongation which causes the shoot to bend toward the light

47
Q

Define photoperiodism

A

ability of an organism to detect day length to ensure that events occur at the right time of year, which allows seasonal response

48
Q

What are examples of plant responses that are controlled by day length

A

initiation of flowering, asexual reproduction, formation of storage organs and onset of dormancy

49
Q

What is the determining factor in flowering

A

day length rather than the accumulation of photosynthate

50
Q

What are the 2 main categories that flowering plants fall into and define each

A

short day plants = flower only in short days or flowering is accelerated by short days
long day plants = flower only in long days or flowering is accelerated by long days

51
Q

Define critical day length

A

the certain duration when plants exceed this day length, they promote flowering in long-day plants and less than this length they promote flowering in short-day plants

52
Q

What are the 3 adaptations that plants exhibit to avoid the ambiguity of the day-length signal

A
  1. juvenile phase that prevents plants form responding to a day length during spring
  2. coupling of a temperature requirement to a photoperiodic response
  3. some plants distinguish between shortening and lengthening days
53
Q

what are the 2 categories of dual day-length plants

A

long-short-day plants = flower after long days followed by short, respond to shortening (flower in late summer and fall)
short-long-day plants = short days followed by long days, respond to lengthening days (flower in spring in response to lengthening days)

54
Q

Define day neutral plants

A

are insensitive to day length, they flower under any photoperiodic condition
ex. desert plants

55
Q

Define endogenous oscillator

A

an internal pacemaker mechanism that circadian rhythms are based on, not based on light or darkness! endogenous oscillators are regulated by four sets of genes expressed in dawn, morning, afternoon and evening

56
Q

what photoreceptors influence circadian rhythms

A

phytochromes primarily, then cryptochromes

57
Q

flowering of short day and long day plants are primarily determined by what

A

duration of darkness
(because long day plants could flower in short days as long as the following night/darkness was shorter to pretend it was a long day in comparison)

58
Q

Define night break

A

a short exposure to light that can make dark periods ineffective by this short interruption

59
Q

the inhibition of flowering in short day plants by night breaks is a physiological process under the control of what photoreceptor

A

phytochromes

60
Q

a night break can become effective in short day plants if…

A

the light is sufficient to convert the pigment back to inactive Pr form and restores the flowering response (if Pfr is present it inhibits flowering)

Plant Phys (15 decks)

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