temperature relations of plants plants and endothermic homeothermic animals differ in how they...
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Temperature Relations of Plants
Plants and endothermic homeothermic animals differ in how they regulate their body temperature
Leaf Energy Budget
Qabs = Qrad + Qconv + Qtrans
Abs = energy absorbedRad = energy lost by radiationConv = energy lost by convectionTrans = energy lost by transpiration
Environmental variables: light, air temperature, humidity
Plant characteristics: leaf color, leaf shape, leaf angle, stomatal responses, height above soil surface
Patterns of Plant Responses to Temperature
Q10 = rate at temperature ‘T’ + 10 C/ rate at temperature ‘T’If <2, then physical limitation; if >2, then process under metabolic control
Plant responses to temperature show phenotypic plasticity
Atriplex confertifolia (Salt Bush) -cold desert plant
Atriplex vesicaria - warm desert plant
Responses to Low Temperature – Tropical/Subtropical Plants
Lowered metabolic rate, slower growth, altered development
Chilling injury: injury when temperature drops below a critical temperature ‘Tm’ (not freezing)
Cellular membranes go from fluid to solid and do not function
Result: death of plant
How does ice crystal formation kill a cell?
Ice crystal formation inside a cell disrupts internal membranes and other structures
Ice crystal formation outside a cell causes internal dehydration and damage to sensitive proteins
Temperature and drought stress are very similar!
Responses to Low Temperature – Temperate Plants
Lowered metabolic rate, slower growth, altered development
Induction of specific genes results in specific avoidance mechanisms:
↑carbohydrates and other solutes; leads to lowering of freezing point (sound familiar?)
↑degree of unsaturation of membrane lipids: membrane more fluid at lower temperatures
↑super cooling of tissue water: ice crystals do not form without nucleation sites until -37 C
Responses of plants to high temperatures
Heat dissipation through emission of long wave radiation, convection and transpiration*
Drought stress causes stomates to close, leading to increase in leaf temperature; if temperature rises to 45 – 55 C, (for most plants) thermal injury or death results
Hah! We can survive at 65 to 70 C!
Responses of plants to high temperatures – heat shock proteins
HSP (heat shock proteins) – synthesized in response to exposure to elevated temperatures
-act as molecular chaperones to protect proteins from heat denaturation
-related to “acquired thermotolerance” 1 - 28 C, 2h
2 - 45 C, 2h3 - 40 C 15’45 C, 2h4 - 40 C 30’45 C, 2h5 - 40 C 1 h45 C, 2h
Fire – Ultimate Temperature Stress
Natural feature of ecological zones with dry season or during dry years
Heat in fire depends on quantity and quality of available combustible material
“Cold” fire: trees survive, nutrients released, seeds in soil break dormancy
“Hot” fire: living vegetation including trees are killed; longer ecosystem recovery time; related to build-up of brush and other fire suppression strategies
Effect of temperature on plant development
Thermoperiod – temperature alternation between day and night related to developmental events:
Tropical plants ~3 CTemperate plant 5 – 10 C
-germination-vegetative development-flowering-fruit and seed development-senescence (death) & dormancy
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