chapter 39: plant responses to external signals

Question 1

What is sensed at the coleoptile tip?

Answer 1

light responsible for triggering phototropism

Question 2

What does light do?

Answer 2

Cues many events in plant growth/development

Question 3

What is photomorphogenesis?

Answer 3

Its the effects of light on plant morphology

Question 4

What can plants detect?

Answer 4

direction, intensity and wavelength (color)

Question 5

What is the action spectrum?

Answer 5

Graph that depicts relative response of a process to different wavelengths of light.

Question 6

What do photoreceptors do?

Answer 6

mediate different plant responses

Question 7

What are the two major classes of light receptors?

Answer 7

1. blue-light receptors: control hypocotyl elongation, stomata opening and phototropism
2. phytochromes: contains pigments absorbing mostly red light, regulating seed germination and shade avoidance

Question 8

How does order of red and far-red illumination affect seed germination?

Answer 8

• red light increases germinations
• far-red light inhibits germinations

Question 9

What do light and temperature regimes do?

Answer 9

Trigger oscillation

Question 10

What is a photoperiod?

Answer 10

relative lengths of night and day (are environmental stimulus

Question 11

What is photoperiodism?

Answer 11

Physiological response to photoperiod

Question 12

What are the different types of plants in regards to light periods?

Answer 12

1. short-day plants: light period is shorter than a critical length
2. long-day plants: light period is longer than a certain number of hours
3. day-neutral plants: controlled by plant-maturity, not photoperiod

Question 13

What are the different types of plants in regards to critical night lengths?

Answer 13

1. short-day plants: critical night lengths sets a minimum number of hours of darkness.
2. long-day plants: critical night lengths sets a maximum number of hours of darkness.

Question 14

What is vernalization?

Answer 14

cold pretreatment to induce flowering

Question 15

what is florigen?

Answer 15

a hypothetical flowering signal molecule.

Question 16

What are the different environmental circumstances using development/physiological mechanisms?

Answer 16

1. phototropism: response to light
2. geotropism: response to gravity
3. chemotropism: response to chemical substances
4. hydrotropism: response to water
5. thigmotropism: response to mechanical stimulation

Question 17

What is gravitropism?

Answer 17

Response to gravity
roots have a positive gravitropism
shoots have a negative gravitropism

Question 18

What is thigmomorphogenesis?

Answer 18

changes in form that results from mechanical disturbance

Question 19

What is thigmotropism?

Answer 19

Growth in response to touch

Question 20

What are action potentials?

Answer 20

transmission of electrical impulses making a mechanical stimulation making rapid leaf movements

Question 21

What are the two types of stresses?

Answer 21

1. biotic stress: bacterial, fungi, viral pathogens, insects and nematodes
2. abiotic stress: salinity, drought, light, temperature, nutrient deficiency

Question 22

How do plants survive flooding?

Answer 22

enzymatic destruction of root cortex creates air tubes that help plants survive oxygen deprivation

Question 23

How do plants survive droughts?

Answer 23

They reduce transpiration, by closing stomata, they reduce exposed surface are, and sometimes shed leaves. Shallow roots are inhibited from growing, but not deeper roots

Question 24

What does evaporative cooling do?

Answer 24

Helps cool leaves (transpiration)

Question 25

What do heat-shock proteins do?

Answer 25

They protect other proteins from heat stress

Question 26

What does salt stress do and what is the cells response?

Answer 26

1. it lowers water potential
2. reduces water intake.
   The cell then produces certain solutes at high concentrations which keeps water potential of cells more negative than soil solution

Question 27

What does cold stress do and how do cells react?

Answer 27

1. decreases membrane fluidity
2. alters lipid composition of membranes
3. freezing, ice forms in plants cell walls and intracellular spaces
   Plants have antifreeze proteins that prevent ice crystal formation

Question 28

What is herbivory?

Answer 28

animals eating plants

Question 29

What are the defenses against herbivores?

Answer 29

1. physical defense: thorns and trichomes
2. chemical defense: distasteful or toxic compounds
3. mind-altering effects: hallucinogenic and psychedelic

Question 30

What are the line of defense against pathogens?

Answer 30

1. barrier presented by epidermis and periderm
2. immune responses where chemical attacks are aimed at isolating pathogen and preventing its spread.

Question 31

What can pathogens that can deliver effectors do?

Answer 31

They can suppress PAMP-triggered plant immunity

Question 32

What are effectors?

Answer 32

pathogen-encoded proteins

Question 33

What is effector-triggered immunity?

Answer 33

its the action of 100 disease resistance (R) genes where each R protein is activated by specific effector

Question 34

What are R proteins?

Answer 34

Protein that activates plant defenses and triggers signal transduction pathways

Question 35

What are the 4 hypersensitive responses and what do they do?

Answer 35

1. stomatal closure: prevents more pathogen cells to enter
2. production of toxins: molecules targeted to pathogen
3. reinforcements: neighbouring plant cell walls limit movement of pathogen
4. suicide of cells: rapid in infected region

Question 36

What does hypersensitive responses produce?

Answer 36

It produces a signal that indices systematic acquired resistance (SAR)