Lecture 7

Question 1

true or false; the circadian clock is the internal clock

Answer 1

true

Question 2

What are the 4 ways that plants response to changes in the environment

Answer 2

1. ) Change in growth patterns
2. ) sudden movements
3. ) biochemical changes
4. ) changes in gene expression

Question 3

Define tropism

Answer 3

plant organs can grow outwards or away from stimuli

Question 4

What are the 4 major types of tropsim

Answer 4

Phototropism
Gravitropism
Thigmotropism
Chemotropism

Question 5

Define phototropism

Answer 5

bending in response to the light
; positive phototropism in shoots
; negative phototropism in roots

Question 6

Define gravitropism

Answer 6

(geotropism) growth in response to gravity

; positive in roots, negative in shoots

Question 7

Define thigmotropism

Answer 7

growth in response to pressure (touch)

; positive in tendrils of creepers

Question 8

Define chemotropism

Answer 8

growth in response to chemicals

; positive hydrotropism in roots (grow towards water)

Question 9

What is the signalling pathway of tropism

Answer 9

stimulus (touch, light, heat,etc)
sensor (receptor)
signalling mechanism
response (often asymmetric growth)

Question 10

What senses gravity in roots

Answer 10

may be perceived by specialized plastids called statoliths

- filled with starch grains

Question 11

Where are statoliths found

Answer 11

found in root cap cells and in shoot vascular bundles

- sediment (collect together) in response to gravity

Question 12

What are other examples of plastids

Answer 12

chlorplasts
amyloplasts
chromoplasts

Question 13

true or false; mutants lacking statoliths can still partly sense gravity

Answer 13

true

Question 14

What role does auxin play in gravitropism in roots

Answer 14

In roots gravity sensing may lead to:
- more Ca2+ and auxin in lower side of root
- increased auxin inhibits elongation in these cells
- root grows down
(roots are more sensitive to auxin concentrations)

Question 15

What role does auxin play in shoot gravitropism

Answer 15

gravity sensing leads to:

• auxin redistribution to lower side of shoot
• cell elongation
• shoot grows up

Question 16

Overall what is auxins role in the growth of plants

Answer 16

ensures that a seed germinates, seedling grows in the correct direction, regardless of orientation of the seed

Question 17

Define nastic movements

Answer 17

non directional responses to stimuli; the movement can be due to changes in turgor (rapid) or growth
- independent of stimulus direction

Question 18

What are examples of plants that are “touch specialists”

Answer 18

venus fly trap
sundew
mimosa leaf closure

Question 19

What are rapid movements in plants carried out by

Answer 19

pulvini organ

Question 20

What is a pulvini

Answer 20

joint like thickenings at base of leaf or petal

Question 21

Describe the process of the rapid movement carried out by a pulvini organ

Answer 21

1. ) initial stimulation (cold, heat, etc..)
2. ) signalling to pulvinus
3. ) K+ ions pumped in/out increase/decrease osmotic pressure
4. ) movement of water in/out of cells
5. ) changes in turgor pressure
6. ) movement of leaves/petals

Question 22

How is the signal transmitted to the pulvini

Answer 22

“electrical” like signal- moving ions
~ 1cm/s
via the plasmodesmata cell to cell
- Ca2+ ions trigger response and involved in propagation along with K+

Question 23

What are examples of biotic stress

Answer 23

herbivore
pests
diseases

Question 24

What are examples of abiotic stresses

Answer 24

cold
heat
drought
flooding- anaerobic (anoxia)
nutrient deficiencies 
toxicities (chemical)
winds, touch

Question 25

what has been noticed when Arabidopsis is grown with exposure to wind at random intervals

Answer 25

shorter plant
tougher stem
- enables to withstand windy conditions

Question 26

What is the reason why most house plants die

Answer 26

overwatered house plants suffocate

• suffocate because the soil lacks the air spaces to provide oxygen for cellular respiration in the root
• soil gets heavy

Question 27

How do maize adapt to anaerobic stress

Answer 27

formation of air tubes in roots (to increase respiration)
like snorkels (rice example)
provides oxygen to submerge roots

ethylene - triggered cell death

Question 28

What are resurrection plants

Answer 28

grow again when conditions are right; seeds survive

Question 29

What are secondary metabolites

Answer 29

• plants are sessile so chemical defenses are crucial

- plants make a huge array of chemicals via secondary metabolism

Question 30

what are examples of secondary metabolites made by plants

Answer 30

terpenoids
alkaloids
phenolics

Question 31

true or false; plants remain the predominant source of new drugs

Answer 31

true

Question 32

What does Willow bark provide

Answer 32

aspirin

Question 33

what does fox glove provide

Answer 33

source of digitalis (treatment for cardiac problems)

Question 34

what does pacific yew provide

Answer 34

source of taxol (treatment for cancer)

Question 35

what does coffee and tea provide

Answer 35

source of caffeine (stimulant)

Question 36

How are stress genes induced

Answer 36

• transcription factors are activated that regulate a cascade of genes
  eg. heat shock genes
  eg. anti freeze genes in cold shock
• induced genes have adaptive/protective role against stress
• many genes are induced by multiple stresses
• utilize knowledge of TF and stress genes to generate transgenic plants protected against the stress

Question 37

true or false; more than 15% of Arabidopsis genes are stress genes that are inducible by abiotic stresses

Answer 37

true

Question 38

what senses phototropism

Answer 38

blue light receptor