Light as an Environmental Signal

Question 1

What levels of irradiance is there high and low in the canopy?

Answer 1

High: high irradiance
Low: low irradiance

Question 2

What is irradiation?

Answer 2

The amount of light on a surface per area per second.

Question 3

What light penetrates the furthest into the canopy?

Answer 3

Far red light

Question 4

How can plants tell what their current and future competition is?

Answer 4

Current: R:FR ratio from top
Future: R:FR ratio from side

Question 5

What is photomorphogenesis?

Answer 5

The origin of the form of a plant in response to light

Question 6

What is phytochrome?

Answer 6

A photoreceptor
Measures light quality by sensing red and far-red light (LFR)
Measures light quantity by measuring photons (VLFR)

Question 7

What are the phytochrome mediated responses?

Answer 7

• LFR: low fluence response
• VLFR: very low fluence response
• HIR: high irradiance response

Question 8

What two forms can phytochrome exist in?

Answer 8

Pr: inactive
Pfr: active

Question 9

What activates Pfr?

Answer 9

Red light activates, far-red inactivates

Question 10

What does the proportion of Pr to Pfr depend on?

Answer 10

R:FR ratio

Question 11

What percentage of phytochrome is Pr and Pfr in 600nm?

Answer 11

Pr: 20%
Pfr: 80%

Question 12

What percentage of phytochrome is Pr and Pfr in 730nm?

Answer 12

Pr: 97%
Pfr: 3%

Question 13

What is a LFR (low fluence response)

Answer 13

Senses light quality
Promoted seed germination
Stimulated by red light. Inhibited by far-red
Can be far-red reversed.

Question 14

What is a VLFR (very low fluence response)

Answer 14

Acts as a photon detector
Can be triggered by red or far-red light
Not far-red reversable

Question 15

What is a HIR (high irradiance response)

Answer 15

Detects irradiance
Can be triggered by red or far-red light
Not far-red reversable
Activation of Pfr requires an intermediate state, in high irradiance, more phytochrome is in intermediate state which triggers HIR.

Question 16

How many phytochrome genes does Arabidopsis have?

Answer 16

5
PhyA, PhyB, PhyC, PhyD, PhyE

Question 17

How can a GFP (green fluorescent protein) track phytochrome?

Answer 17

GFP binds to phytochrome gene, which makes phytochrome fluoresce green.
Phytochrome moves to nucleus when activated, which shows the nucleus as green.

Question 18

What happens to PhyA in light?

Answer 18

It is destroyed
There is a lot of PhyA in etiolated plants (plants grown in darkness)