C.39 - Plant Response

Question 1

Steps of the Signal Transduction Pathway

Answer 1

• Reception (receptors detect change in stimuli response)
• Transduction (signals from receptors are transferred and amplified via second messengers)
• Response (STP regulates cellular activities)

Question 2

STP in De-etiolation.

Answer 2

Receptor is phytochrome (it detects light) which activates Ca2+ and increases its concentration in cytosol. This activates cGMP. Activates enzymes which function in photosynthesis, affect plant hormone levels, and supply the chemicals for chlorophyll production.

Question 3

Hormone/growth regulators

Answer 3

Chemical signals that modify or control one or more specific physiological process

Question 4

Acid growth hypothesis

Answer 4

Ability of plant cell walls to elongate or expand at low (acidic) pH. Auxin causes protons to be pumped into cell wall, causing it to be acidic. Activating Expansin which loosens the cell wall, which allows the cell volume to increase by turgor and osmosis.

Question 5

Blue Light Receptor

Answer 5

Controls hypocotyl elongation (part of the stem), stomatal opening, and phototropis

Question 6

Phytochromes and seed germination

Answer 6

Exist in two photoreversible states (Pr(red) to Pfr (far-red light)). Photoreceptor responsible for opposing effects of red and far-red light. Red light increased germination, while far-red light inhibits germination

Question 7

Red and far-red effect on seed germination

Answer 7

Red light increased germination, while far-red light inhibits germination. Sunlight increases ratio of Pfr to Pr, and triggers germination (Pr

Question 8

Phytochromes and shade avoidance

Answer 8

Shaded plants receive more far-red than red light so the phytochrome ratio shifts in favour of Pr when trees shaded. Shifts the resources to growing taller, rather then branching which it will do in direct sunlight

Question 9

Circadian rhythm

Answer 9

Cycles about 24 hours long and governed by internal “clock” in response to changes in light, temperature and relative humidity based.

Question 10

Short-day and long-day plants

Answer 10

Short-day plants (long night plants) governed by set minimum number of hours of darkness. Long-day plants (short night plants) governed by set maximum number of hours of darkness.

Question 11

How Pfr and Pr are affected by light

Answer 11

During the night Pfr gradually reverts to Pr; by sunrise all the phytochromes are in the Pr form. Daytime Pfr levels increase because Pr absorbs red light and becomes Pfr.

Question 12

Florigen

Answer 12

Unidentified molecule the gives the flowering signal.

Photoperiod detected by leaves, which cue buds to develop as flowers.

Question 13

Gravitropism

Answer 13

Plants response to gravity, detected by statoliths.
Positive: growth down (eg. roots)
Negative: growth up (eg. shoots)

Question 14

Thigmotropism

Answer 14

Growth in response to touch; due to a transmission of action potentials.

Question 15

Location of Auxin

Answer 15

Produced predominantly in shoot tips and is transported down the stem via unidirectional transport

Question 16

Location of Cytokinins

Answer 16

Produced in actively growing tissues such as roots, embryos, and fruit

Question 17

Location of Giberellins

Answer 17

Produced in young roots and leaves

Question 18

Location of Jasmonates

Answer 18

Produced in response to wounding

Question 19

Function of Auxin

Answer 19

Stem elongation (major site of production is in the apical meristem). Also role in plant pattern, acid growth, and with cytokinins in cell division and differentiation.

Question 20

Function of Cytokinins

Answer 20

Stimulate cell division and differentiation with auxin.
Role in Apical Dominance (axillary bud growth)
Anti-Aging Effects by inhibiting protein breakdown, stimulating RNA and protein synthesis, and mobilizing nutrients from surrounding tissues

Question 21

Function of Giberellins

Answer 21

Stem elongation, fruit growth, and seed germination (when in contact with water)

Question 22

Function of Brassinosteroids

Answer 22

Induce cell elongation and division in stem segments. Slow leaf abscission (dropping leaves) and promote xylem differentiation

Question 23

Function of Jasmonates

Answer 23

Plant defense and development. Also plays a role in Nectar secretion, Fruit ripening, Pollen production, Flowering time, Seed germination, Root growth, Tuber formation, Mycorrhizal symbiosis, Tendril coiling

Question 24

Function of Abscisic Acid

Answer 24

Slows growth!
–Seed dormancy ensures that seed will germinate only in optimal conditions
–Drought tolerance: ABA primary internal signal that enables plants to withstand drought

Question 25

Function of Strigolactones

Answer 25

–Stimulate seed germination
–Help establish mycorrhizal associations
–Help control apical dominance

Question 26

Function of Ethylene

Answer 26

Stress response: drought, flooding, mechanical pressure, Injury, infection
Also aging, leaf abscission, and fruit ripening.
Triple response to mechanical stress: slowing of stem elongation, a thickening of the stem and horizontal growth