Seasons and Temperature Flashcards
What are variable factors in seasons?
- Water availability
- Temp
- Pests/herbivores
- Sunlight
- Nutrients
What is a chilling injury?
Exposure to low temps but do not cause freezing.
What are symptoms of a chilling injury?
- Slowed growth
- Reduced photosynthesis
- Loss of solutes from cell
- Water soaked lesions
How can plants acclimate to chilling temperatures?
Change in membrane proteins / structure / fluidity
What forms are membranes in in low temps and high temps?
Low- semi crystalline
High- fluid
Are plants richer in saturated or unsaturated fatty acids?
Unsaturated fatty acids
What is a membrane containing many saturated fatty acids like at high temps and low temps like?
High temps: more stable
Low temps: unstable, semicrystalline more readily
What is a membrane containing many unsaturated fatty acids like at high temps and low temps like?
High temps: unstable, more readily fluid
Low temps: more stable
What do desaturase enzymes do?
Increase desaturation of fatty acids, plants acclimatise to lower temps.
But plants at risk of heat stress.
What is a freezing injury?
Formation of ice crystals in cell, disrupts integrity of cell.
Freezing of the cytoplasm causes irreversible damage.
Describe the process of freezing in plants:
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.
Why are crops sprayed with water in cold temps?
Protects plants from freezing damage.
Layer of ice on the outside will not damage the plants, and releases heat for the plants.
What are some mechanisms of freezing tolerance?
- Dessication
- Dormancy
- Antifreeze
- Allow ice crystal formation in non-essential parts of the cell
What plant hormone stimulates dormancy?
ABA inhibits cell division, leading to dormancy
What plant hormone breaks dormancy?
GA promotes growth and breaks dormancy
What happens in 2 step hardening of some woody species?
Stage 1: hardening
- triggered by cool temps and short days
- Water removes from xylem
Stage 2: full hardening
- tissues become resistant to -100
What molecules can decrease the freezing point of cells?
Solutes such as sucrose decrease freezing point, inhibiting crystal formation
How do antifreeze proteins work?
They bind to the edge of growing ice crystals to prevent further growth.
What is deep supercooling?
(Ice crystals grow from nucleation points)
No nucleation points in cell means no ice crystal formation until -40
What is dessication resistance?
Some plants have extracellular spaces to accomodate crystal formation
Mutations in lipids = resistant to dessication.
What are the effects of freezing resistance on the landscape?
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.
What process can maintain leaves in intense heat?
Transpiration
What can denatured proteins be refolded by?
Chaperonins
