Detecting the Environment

Question 1

phytochrome red light sensing function

Answer 1

Can absorb red and far-red light, but not simultaneously. Pr absorbs red light and becomes active Pfr; Pfr can absorb far-red light and return to inactive Pr.

Question 2

The role of phytochrome in light sensing

Answer 2

light/dark sensing; R/Rf ratio is much lower in the dark.

Question 3

the role of phytochrome in plant competition

Answer 3

Plants absorb red and blue light, but scatter far red light. A plant can detect proximity or shading of neighbouring plants by decreased R/FR ratio.

Question 4

Phytochromes found in arabidopsis

Answer 4

5 phytochromes (A-E) ; A and B are the most important

Question 5

functions of phytochrome A

Answer 5

phytA protein represents the ‘Light-Labile’ pool. PHYA is degraded in the light so mainly present in dark-grown plants. PHYA allows plants to be sensitive to very low light fluence levels (VLFR) and causes the Far-red high irrandiance response (FR-HIR).

Question 6

Cryptochrome functions

Answer 6

allowing blue light sensing of plants; FAD is the chromophore of these proteins

Question 7

Phototropins

Answer 7

another blue light receptor family of proteins; specifically function in detecting the direction of light exposure.