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L3 Plant Sciences > Week 14 L6: Abiotic Environment - Light as a Growth Regulator > Flashcards

Week 14 L6: Abiotic Environment - Light as a Growth Regulator Flashcards

1
Q

What does light perception regulate?

A 
Germination
Post-emergence dark growth (skotomorphogenesis)
De-etiolation
Photomorphogenesis
Shade avoidance
Flowering time
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2
Q

What is skotomorphogenesis?

A

growth in the dark

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3
Q

What does a plant do when no light vailable?

A

Seedling trait during conditions unable to support photosynthesis
Adaptive, light seeking response
No functional chloroplasts

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4
Q

What is it called when plants grow in light?

A

photomorphogenesis

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5
Q

What does a plant do when in light growth?

A

De-etiolation
Chloroplasts activated
Switch to photomorphogenesis requires minimal light

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6
Q

Can a light change from light growth to dark growth?

A

no - a split second of light causes it to be irreversible committed to photomorphogenesis

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7
Q

What is fluence response?

A

period of time of exposure to light

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8
Q

Does skotomorphogenesis occur in adult plants?

A

NO restricted to seedlings

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9
Q

What regions of the spectrum can plants perceive light?

A

UV – UVR8, Cryptochromes
Blue – Phototropins, Cryptochromes, FKF1, (Phytochrome)
Red – Phytochromes
Far red – Phytochromes

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10
Q

What are the phytochromes?

A

a class of photoreceptor in plants, bacteria and fungi used to detect light. … They regulate the germination of seeds (photoblasty), the synthesis of chlorophyll, the elongation of seedlings, the size, shape and number and movement of leaves and the timing of flowering in adult plants.

A large receptor family sensitive to red and far-red light.

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11
Q

What region do phytochromes observe light?

A

red

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12
Q

Where are phytochromes located in a plant?

A

cytoplasm in their dark state but are transported into the nucleus upon light activation.

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13
Q

When will plants undergo skotomorphogenesis?

A

usually during seed development (germinating seedlings) when it is in the soil and looking for light.

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14
Q

What is it called when plants undergo skotomorphogenesis?

A

dark growth

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15
Q

Do plants in skotomorphogenesis undergo photosynthesis?

A

NO, they have no functional chloroplasts

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16
Q

What is hypocotyl?

A

short for “hypocotyledonous stem”, meaning “below seed leaf”) is the stem of a germinating seedling, found below the cotyledons (seed leaves) and above the radicle (root).

which is the transition zone between the shoot and root; and the radicle.

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17
Q

What is the radicle?

A

Primary root
first organ to appear when a seed germinates.

Grows down into the soil, anchoring the seeding.

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18
Q

How does a plant in dark growth grow?

A

It puts all its reserves into elongating the hypocotyl.

Leaves are curled up to help it push through the soil

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19
Q

Do plants growing in the dark have roots?

A

No, roots will develop when the plant has light and can photosynthesise.

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20
Q

What is de-etiolation?

A

greening-up

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21
Q

What is an apical hook?

A

When the leaves on a skotomorphogenesis are curled up

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22
Q

How many photochromes does arabidopsis have?

A

5

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23
Q

What are the phytochromes called in arabidopsis?

A

A, B, C, D and E.

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24
Q

What is the inactive form of phytpchromes?

A

P(R)

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25
Q

What is the active form of phytochromes?

A

P(FR)

26
Q

How do the phytomers become active?

A

absorbing red light

27
Q

How are phytomers converted back to inactive state?

A

far red light absorbed

28
Q

What is the term used to describe the active-inactive forms of arabidopsis phytomers?

A

photoreversible switch

29
Q

What wavelength is red light?

A

650-680nm

30
Q

What wavelength is far red light?

A

710-740nm

31
Q

What form of red light inhibits responses?

A

far red, changes the phytomer to the inactive form.

32
Q

What about the phytomers determines the magnitude of response?

A

R:FR mediate size of response.

33
Q

Why are the phytomers photoreversible?

A

so they can adapt to environmental conditions.

Light levels, direction, quality and quantity.

34
Q

What to phytochromes operate in?

A

Fluence Response modes

35
Q

What are the 3 levels of fluence?

A

VLFR
LFR
High Irradiance response (HIR)

36
Q

How much light does a plant with VLFR get?

A

less that 5 microseconds.

37
Q

How many molecules will be converted from the F form to the FR form?

A

not many.

38
Q

What is the role of molecules in the FR form?

A

massive effect on plant development.

39
Q

What is the predominant form of phytochrome when a seed is trying to germinate?

A

PHYA in PR form (inactive)

40
Q

What phytochromes control the switch from skoto- to photomorphogenesis?

A

A and B

41
Q

What phytomer is abundant in dark growth?

A

A

42
Q

What form of the phytomer is rapidly degraded?

A

fr (active)

43
Q

What form of the phytomer allows for a burst of signalling?

A

FR (active)

44
Q

When is the growing plant exposed to red light?

A

When it reaches the soil surface

45
Q

When is phytomerA active?

A

when the hypocotyl reaches the soil surface and absorbs red light. PHYA is active. and photomorphogenesis is active.

46
Q

What is the role of PHYA?

A

to detect the slightest bit of red light that tells them there is enough light to start photosynthesising.

Acts as a Red VLFR sensor in this instance and detects soil surface.

47
Q

What happens to PHYA when the plant changes to photomorphogenesis?

A

PHYA is degraded.

48
Q

What phytomers are involved in photomorphogenesis?

A

PHYB with help from CD and E PHYB acts in LFR mode and takes over once initial switch has occurred..

Depending on R:FR

49
Q

How can plants tell if they are being shaded by another plant or less sunlight?

A

The ratio of far red light to red light.

50
Q

What type of radiation do plants emit a lot of?

A

far red light

51
Q

What is the dominant phytochrome effecting photomorphogenesis?

A

PHYB

52
Q

What happens if you KO PHYB?

A

It will look like the plants are doing a shade avoidance response. Even though the plant is growing in white light

53
Q

What is the default growth pathway?

A

shade avoidance response. But PHYB work by suppressing the pathway.

54
Q

How do plants regulate shade avoidance response?

A

negatively

plants suppress shade avoidance response when B is active.

55
Q

Why do plants flourless far red?

A

It is absorbing too much red light. It emits energy as far red

56
Q

How can a small plant tell it is competing?

A

The larger plants fluoresses far red. The small plant has a higher ratio of far red to red. THE SMALL PLANT CAN TELL ITS COMPETEING BY THIS LOW RATIO OF RED LIGHT BEING ABSORBED.

57
Q

How does a small plant compete for light?

A

The small plant is deprived of red light so it converts its PHYB to the PR (inactive) form. The shade avoidance response is allowed to proceed.

The plant will elongate until it reaches the light and will resume normal growth as the PHYB is in the PFR (active) and a halt is put on the shade avoidance response.

58
Q

What suppresses germination?

A

PHYA in the PR form. acting in HIR mode (sustained period of far red enriched light) suppresses germination.

59
Q

In HIR, what phytochrome is activated in response to far red light?

A

A and will be the inactive form of the phytochrome

60
Q

In HIR do the PHYB make a difference?

A

NO, PHYA overrides it as the conditions are not optimal to germinate due to competition

61
Q

When will germination occur?

A

If the competition subsides and the plant is exposed to red light which will make the phytomers in their active form. This indicates to the plant that it can germinate and its offspring will be able to grow in substantial conditions.

L3 Plant Sciences (17 decks)

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