16.2 Plant Responses To Abiotic Stress

Question 1

What are seven examples of abiotic stress?

Answer 1

Changes in day length

Cold and heat

Lack of water / excess water

High winds

Changes in salinity

Question 2

What are some physiological adaptations of plants to respond to HOT, DRY or extremely WINDY conditions?

Answer 2

Thicker cuticles

Hairy leaves

Sunken stomata

Wilting response

Question 3

What are some physiological adaptations of plants in an aquatic environment?

Answer 3

Aerenchyma

Question 4

What is aerenchyma?

Answer 4

Intercellular spaces containing gas which provides plant roots with oxygen in an aquatic environment

Question 5

Why do deciduous trees in temperate climates lose all of their leaves in winters and remain DORMANT until spring?

Answer 5

Amount of glucose required for respiration to maintain leaves + produce chemicals to protect against freezing
GREATER THAN
amount of glucose produced by photosynthesis

Tree with leaves MORE LIKELY to be blown over by WINTER GALES

Question 6

What do plants express regarding daylight?

Answer 6

Photoperiodism

Question 7

What is photoperiodism?

Answer 7

Sensitivity of plants to a LACK of light in environment

Question 8

What does the sensitivity of plants to dark length result from?

Answer 8

Phytochrome

Question 9

What is phytochrome?

Answer 9

Light-sensitive pigment

Question 10

In what two forms does phytochrome exist?

Answer 10

Pr and Pfr

Question 11

What, regarding phytochrome, changes depending on the LEVELS OF LIGHT?

Answer 11

Ratio of Pr to Pfr

Question 12

What does the lengthening of the dark period during winter trigger?

Answer 12

Abscission and a period of dormancy

Question 13

What is abscission?

Answer 13

Leaf fall

Question 14

Can you describe the responses of the plant leaves to falling levels of light?

Answer 14

1. Concentration of AUXIN DECREASES
2. Leaves produce ethene in response
3. Ethene initiates GENE SWITCHING of cells in ABSCISSION ZOME
4. Production of new enzymes
5. Enzymes digest and weaken cell walls in SEPARATION LAYER
6. Vascular bundles sealed off
7. AND fatty material is deposited in cells on STEM SIDE of separation layer
8. Cells deep in separation respond to hormonal cues by RETAINING WATER and SWELLING
9. Puts more strain on weakened outer layer
10. Further abiotic factors finish process
    E.g. strong autumn winds or low temperatures
11. Neat, waterproof scar left behind

Question 15

Where I St he abscission zone found?

Answer 15

Base of leaf stalk

Question 16

What is the abscission zone made up of?

Answer 16

TWO layers of cells sensitive to ETHENE

Question 17

What are the cell walls in the OUTER LAYER of the abscission zone known as?

Answer 17

Separation layer

Question 18

What does the protective scar left behind after the leaf falls do?

Answer 18

Prevents entry of pathogens

Question 19

How plants prevent their cells from freezing?

Answer 19

CYTOPLASM and SAP IN VACUOLES of plant cells contain SOLUTES which LOWER freezing point

Question 20

What things act as antifreeze in plants?

Answer 20

Sugars

Polysaccharides

Amino acids

Proteins

Question 21

How does a plant cool down?

Answer 21

Stomata opens

Water evaporates from cells in TRANSPIRATION

Question 22

What is the opening and closing of the stomata in repose to abiotic stresses under the control of?

Answer 22

Hormone ABA

Question 23

How does a plant respond to ABA tofalling soil water levels?

Answer 23

1. Soil water levels falls
2. Plant ROOTS produce ABA
3. Transported to leaves
4. Binds to receptors on plasma membrane of STOMATAL GUARD CELLS
5. ABA activates changes in IONIC CONCENTRATION of guard cells
6. Water potential reduced
7. Turgor of cells reduced
8. Guard cells close stomata
9. Water loss by transpiration is greatly reduced