Transcript Document 7834225

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 absorbed
Rad = energy lost by radiation
Conv = energy lost by convection
Trans = 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
Plant responses to temperature reflect genetic
differences and geographical distributions
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 photosynthesis
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, 2h
3 - 40 C 15’45 C, 2h
4 - 40 C 30’45 C, 2h
5 - 40 C 1 h45 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 C
Temperate plant 5 – 10 C
-germination
-vegetative development
-flowering
-fruit and seed development
-senescence (death) &
dormancy
Characteristics of Leaf
Senescence
↓growth and
metabolism
↑ABA, ethylene
↓chlorophyll
(carotenoids ‘appear’)
↑respiration
↑anthocyanins
↑nutrient recovery and
transport to mother
plant
↑leaf abscission