Plant Responses

Question 1

What are typical responses to red light?

Answer 1

• Seed germination
  – Development of primary leaves (1st
  true leaves/foliage leaves)
  – Anthocyanin (pigment) production
  – Inhibits internode elongation
  – Chlorophyll accumulation

Question 2

What is photomorphogenesis?

Answer 2

Light regulated development

Question 3

What protein pigment absorbs red light?

Answer 3

Phytochrome

Question 4

What are the two forms that phytochrome exists as?

Answer 4

Red-light absorbing (Pr) and far-red light absorbing (Pfr)

Question 5

Can phytochrome (Pr) convert to Pfr and back?

Answer 5

Yes, although once Pr is converted to Pfr a 100% conversion rate back to Pr is not possible.

Question 6

What does red light to to phytochrome?

Answer 6

Red light converts Pr to Pfr

Question 7

What does far-red light do to phytochrome?

Answer 7

Converts Pfr to Pr

Question 8

Why is phytochrome photoreversible?

Answer 8

To account for the environment, a shady canopy rich in far red-light will inhibit the seed germination to wait for more light to increase the chances of maturing in healthy environment.
When a gap in canopy occurs the phytochrome will tune into the increase in red light to shoot and break seed dormancy.
If the canopy above then closes again they will reverse and absorb far -red light and grow skinnier and taller due to this to reach light quicker.

Question 9

What are typical blue light responses?

Answer 9

– Solar tracking by leaves & flowers
– Stomatal opening
– Chloroplast movement – to increase or decrease light absorption according to light conditions
– Cotyledon expansion
– Stimulation chlorophyll synthesis

Question 10

What is positive tropism in plants?

Answer 10

Turning towards stimulus

Question 11

What is positive tropism in plants?

Answer 11

Turning towards stimulus

Question 12

What is a negative tropism?

Answer 12

Turning away from a stimulus

Question 13

What are the types of tropism and their stimuli in plants?

Answer 13

• Phototropism - light
• Gravitropism - gravity
• Thigmotropsim - Touch
• Hydrotropism - water
• Chemotropism - chemical

Question 14

What does the plant use to recognise the direction of gravity?

Answer 14

Heavy starch in statocyte cells, this moves to area of cell closest to ground/gravity pull.

Question 15

Where is the starch sheath located?

Answer 15

At the innermost layer of the cortex.

Question 16

What are nastic movements?

Answer 16

A response that is independent of the direction of the external stimulus, EG the closing up of sensitive leaves to touch like in mimosa or the quick closing of a venus flytrap that has sensed touch.
- Also the opening and closing of flowers in the circadian rhythm.

these movements are reversible, unlike tropisms and require a motor organ such as a pulvinus.

Question 17

Which hormones are involved in flowering?

Answer 17

• Gibberellins (GA)
• Ethylene in bromeliads

Question 18

What is entrainment with the circadian rhythm?

Answer 18

Entrainment is a fundamental property of circadian systems by which the period of the internal clock (tau) is synchronized to the period of the entraining stimuli, EG light from sun and moon.