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LOW TEMPERATURE DAMAGE
HOW CHILLING TEMPERATURES INJURE PLANTS (SLOW DEATH)
1) Increased protein and enzyme breakdown.

2) Increased membrane leakiness

    a) membranes lose selective permeability

    b) often appears deeper green and slightly waterlogged

Sensitive Plants:

  • tropical plants
  • tropical fruits 
  • summer annuals and bedding plants 
  • chilling sensitive vegetables 
HOW FREEZING TEMPERATURES INJURE PLANTS (SLOW OR FAST DEATH)
1) Direct cellular damage - damage to individual cells.

    a) Very rapid temperature drop
         - ice forms in cytoplasm and ruptures cell
         - seldom occurs, but always fatal

    b) Moderate temperature drop
         - ice forms in cell wall and cytoplasm dehydrates
         - most commonly occurs, not fatal to hardy or cold acclimated plants.

    more sensitive vs. more resistant
    young tissue vs. old mature tissue
    growing tissue vs. dormant tissue
    flower buds vs. vegetative buds
    roots vs. shoots
2) Desiccation - excessive drying-out due to cold soil and dry winds.

3) Frost heaving - soil freezes and expands, thus heaving the plant out of the soil.

4) Bark splitting - cambium under bark freezes, expands, then splits the bark.

5) Physical or mechanical breakage (ice damage) - from weight of ice on plant.

6) Sun scald or Southwest injury - excessive desiccation on southwest side of tree;
                                                      sunlight is brightest on the south and west side.