BIO3082 Lecture Notes - Lecture 5: Water Potential, Cuticle, Stunted Growth
Lecture 5 – Water Loss
Water Availability
• Main source of global primary production
• Restricts terrestrial plant productivity in both natural and agricultural settings
• Water – electron donor for oxygenic photosynthesis
o Solvent for cellular metabolism
o Source of turgor in cells and tissues
• Affects distributions of animals due to direct factors (providing hydration) and
indirect factors (providing food through plants)
• Projected changes in precipitation rates are not uniform
o Temperature rise will increase evapotranspiration
Water Loss
• Inevitable during gas exchange
o Rates of water loss – proportional to rate of CO2 uptake in plants and
O2 uptake in animals
• Sites where water evaporates: leaves, alveoli, tracheae
o Tissues are coated in water vapour – ventilated by the atmosphere and
large surface areas
• Water loss correlates with metabolic rate
Routes of Water Loss in Animals and Plants
• In Insects
o Cuticular (through exoskeleton)
o Respiratory (through spiracles)
• In Plants
o Transpiration (through the roots)
▪ Some water used for photosynthesis, most lost by transpiration
through stomata
• Controls stomata through using guard cells: regulates
conflicts between need for CO2 fixation and need for
water conservation
• Can
▪ Passive process: driven by less negative water potential of soil
Short and Long Term Responses of Plants to Drought
Short Term
Medium Term
Long Term
• Sense loss of water
balance → synthesis of
hormone abscisic acid
(ABA)
• Stomata close to minimise
transpiration
• Inhibition of
photosynthesis due to
reduction in CO2 supply
• Decrease in water content
→ turgor loss and leaf
shrinkage
• Osmotic adjustment
(change water potential
by changing distribution
of ions in cells) in leaves
and roots to acquire more
water
• Stunted growth due to
lack of photosynthesis
• Extension of roots into
deeper moist soils
• Wax deposition to
increase thickness of leaf
cuticle
• Leaf abscission to
improve fitness in water-
limited environment
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