Light Control

Question 1

What info does light provide?

Answer 1

Seasons
(Day length/int)

Time of day
(intensity)

Local Habitat
(Vegetation proximity)

Question 2

What limits light availability?

Answer 2

Time of Year

Time of Day

Latitude

Cloud cover
(reduce 3-6x)

Question 3

What has EdUni’s Geosciences weather station found?

Answer 3

Max solar radiation in July

Lowest in January

Correlation with temperature

No correlation with rain

Question 4

Why does light intensity vary during the day?

Answer 4

Intensity decreases as ANGLE of incidence decreases

Question 5

( ! ) What are the 5 Physiological Responses to Low Light Intensity?

Answer 5

1. Longer INTERNODES + STEM
2. Larger LEAF SA
3. Thinner LEAF AND STEM
4. Thinner CUTICLE
5. ONE layer of palisade cells
   (Below epiderm, have chloroplasts)

Question 6

What range of light can plants sense?

Answer 6

UV to Far Red

Question 7

( ! ) has What FOUR things do Phototropins do?

Answer 7

1. Phototrophic growth (duh)
2. Stomata opening
3. Leaf expansion
4. Chloroplast movement

accum at top - Low
hide at sides (protect) - High
retreat to bottom - Darkness

Question 8

What did Briggs and Liscum identify?

Answer 8

Briggs - A blue-activated mem-bound protein (‘90s)

Liscum - nph1 mutant; map to PHOT1 Locus

Question 9

What are Phototropins?

Answer 9

Serine/Threonine KINASES

PHOT1 and PHOT2

Question 10

What domains to Phototropins have?

Answer 10

1. PHOTOSENSORY domain

2. OUTPUT domain

Question 11

What does the Phot PHOTOSENSORY domain do?

Answer 11

LOV 1 + 2 domains:

bind (flavin-based) FMN chromophores
(FMN 2 more active)

Ja is flexible alpha helix

Question 12

What does the Phot OUTPUT DOMAIN do?

Answer 12

Has Ser/Thr Kinase

Enzyme activity (signalling)

Subcellular localisation

Question 13

What does Blue Light promote in a Phot receptor?

Answer 13

A covalent cysteine bond

Active form - cannot absorb BLUE

Question 14

What happens with activation/repression of the Phot protein?

Answer 14

Dark: PS and Kinase domains together

Blue: Ja Helix unfolds

Autophos by ATP

Question 15

What changes with Phot active conformation change?

Answer 15

1. SIGNALLING activation
2. RELOCATION:

PHOT1 @ cyto
PHOT2 @ golgi

(Plas Mem in Dark)

Question 16

( ! ) What FOUR things do Cryptochromes regulate?

Answer 16

1. De-etiolation
2. Stomata opening
3. Plastid Development
4. Flowering Time

Question 17

What did Margaret Ahmad discover?

Answer 17

the cry1 mutant -

discover CRY struc/func

Question 18

What are Cryptochromes?

Answer 18

CRY 1 + 2 + 3

All resemble photolyases
(DNA Repair Enzyme)

CRY 3 has this function
(Operates in CP/Mito)

Question 19

What domains to CRY 1 + 2 have?

Answer 19

1. Photolyase Homo Region
   (PHR) Domain

binds 2 DIFFERENT chromophores
(MTHF And FAD)

2. C-term extension
   (CCE) Domain

Question 20

What do the chromphores binding to the PHR domain do? (CRY)

Answer 20

FAD is main receptor

MTHF absorbs UV and transfers energy to FAD

Question 21

How is CRY activated?

Answer 21

Blue induces neutral FAD RADICAL to form:

> FADH <

(Resting, oxidised form of FAD absorbs blue)

Question 22

What happens to the CRY protein upon activation?

Answer 22

A DIMER forms
(Two PHR domains together)

CCE bits OPEN
(Signalling takes place)

Question 23

Where does CRY accumulate when blue activates it?

Answer 23

I’m NUCLEAR BODIES

(many smol > few large)

CRY2 is light LABILE