Seasons and Temperature

Question 1

What are variable factors in seasons?

Answer 1

• Water availability
• Temp
• Pests/herbivores
• Sunlight
• Nutrients

Question 2

What is a chilling injury?

Answer 2

Exposure to low temps but do not cause freezing.

Question 3

What are symptoms of a chilling injury?

Answer 3

• Slowed growth
• Reduced photosynthesis
• Loss of solutes from cell
• Water soaked lesions

Question 4

How can plants acclimate to chilling temperatures?

Answer 4

Change in membrane proteins / structure / fluidity

Question 5

What forms are membranes in in low temps and high temps?

Answer 5

Low- semi crystalline
High- fluid

Question 6

Are plants richer in saturated or unsaturated fatty acids?

Answer 6

Unsaturated fatty acids

Question 7

What is a membrane containing many saturated fatty acids like at high temps and low temps like?

Answer 7

High temps: more stable
Low temps: unstable, semicrystalline more readily

Question 8

What is a membrane containing many unsaturated fatty acids like at high temps and low temps like?

Answer 8

High temps: unstable, more readily fluid
Low temps: more stable

Question 9

What do desaturase enzymes do?

Answer 9

Increase desaturation of fatty acids, plants acclimatise to lower temps.
But plants at risk of heat stress.

Question 10

What is a freezing injury?

Answer 10

Formation of ice crystals in cell, disrupts integrity of cell.
Freezing of the cytoplasm causes irreversible damage.

Question 11

Describe the process of freezing in plants:

Answer 11

Ice crystallisation starts past 0, (-5.5)
freezing starts in cell wall which releases heat.
All water in apoplast is frozen.
Water moves into cell wall.
Individual protoplasts freeze
All protoplasts freeze
Temp cools to ambient.

Question 12

Why are crops sprayed with water in cold temps?

Answer 12

Protects plants from freezing damage.
Layer of ice on the outside will not damage the plants, and releases heat for the plants.

Question 13

What are some mechanisms of freezing tolerance?

Answer 13

• Dessication
• Dormancy
• Antifreeze
• Allow ice crystal formation in non-essential parts of the cell

Question 14

What plant hormone stimulates dormancy?

Answer 14

ABA inhibits cell division, leading to dormancy

Question 15

What plant hormone breaks dormancy?

Answer 15

GA promotes growth and breaks dormancy

Question 16

What happens in 2 step hardening of some woody species?

Answer 16

Stage 1: hardening
- triggered by cool temps and short days
- Water removes from xylem
Stage 2: full hardening
- tissues become resistant to -100

Question 17

What molecules can decrease the freezing point of cells?

Answer 17

Solutes such as sucrose decrease freezing point, inhibiting crystal formation

Question 18

How do antifreeze proteins work?

Answer 18

They bind to the edge of growing ice crystals to prevent further growth.

Question 19

What is deep supercooling?

Answer 19

(Ice crystals grow from nucleation points)
No nucleation points in cell means no ice crystal formation until -40

Question 20

What is dessication resistance?

Answer 20

Some plants have extracellular spaces to accomodate crystal formation
Mutations in lipids = resistant to dessication.

Question 21

What are the effects of freezing resistance on the landscape?

Answer 21

Timberlines develop when the seedling is LESS freezing tolerant than the mature trees. They are shade tolerant so they can grow in with the mature trees.
Krummhoz zones develop when the seedlings are MORE freezing tolerant than the mature trees.

Question 22

What process can maintain leaves in intense heat?

Answer 22

Transpiration

Question 23

What can denatured proteins be refolded by?

Answer 23

Chaperonins