Lecture 5 Flashcards
(21 cards)
Examples of low water environments?
Urban, dryland systems, polar systems, rainforest canopies.
What is CAM?
Crassulucean Acid Metabolism is a photosynthetic adaptation to fluctuating/periodic water supply.
What plants use CAM?
7% of all flowering species. Cacti and tropical epiphytes such as orchids and bromeliads.
How does it relate to succulence?
CAM is always associated with succulence, at least at a cellular level.
How is CAM different from C4 photosynthesis?
CAM uses a temporal separation of carbon fixation and RuBisCO rather than spatial separation which is used in C4 photosynthesis.
Describe the process of CAM during the night.
Stomata is open and CO2 is fixed into malate by PEP carboxylase and is stored in a vacuole as C4 acid.
Carbohydrates are broken down to provide the PEP for PEP carboxylase
Describe the process of CAM during the day.
Stomata is closed and malate is decarboxylated into CO2 and used in the calvin cycle.
CHO is reformed during the day following malate decarboxylation and CO2 fixation.
Why is CAM less efficient than C4?
As in CAM there is no activity during the day.
What is the advantage of CAM?
It allows plants to grow in conditions unavailable to other species.
What is faculative CAM?
CAM that can be turned on/off depending on environmental conditions.
It’s an acclimatory and completely reversible response that requires lots of gene expression and can be expressed deferentially in tissues.
What are some examples of faculative CAM plants?
Ice plant, Clusia minor, Surinam purslane.
When is faculative CAM activated?
When plants are subjected to stress: drought, salt, light, long days, nitrogen/phosphate deficiency.
Why is aquatic CAM advantageous?
CO2 diffuses 10,000 times slower in water, especially at low pH. Global warming increasing ocean acidity will result in CAM being more advantageous. Competition for CO2 is high in the sea, especially during the day.
How does CAM help water-use efficiency?
Water-use efficiency is 10 times higher in CAM than C3/C4 plants, this reduces CO2 uptake. CAM plants only open their stomata at night when transpiration rates are low. Because of this CAM will likely become more widespread with global warming.
What are some whole plant adaptations in non-CAM plants to lack of water?
Succulence: stores water in cells.
Reduced leaves: reduces transpiration, water already limits photosynthesis so large leaves aren’t needed.
Compact growth form: low S.A:V ratio reduced transpiration.
Ribs: allow plant to expand when water levels increase.
Thick cuticle: prevents water loss.
Surface roots: spread wide and shallow to catch rain.
How does increasing the boundary layer of still air around the leaf conserve water?
Leaf hairs (trichomes), spikes, sunken stomata and rolled leaves prevent evapotranspiration.
How is the stomatal pore closed?
When the guard cells are flaccid.
How is the stomatal pore opened?
H+ ions forced out of cell, creating ionic imbalance that forces potassium ions in and water in through aquaporins. Guard cell wall is thickened on the inside so as they expand they bow outward to create a 5-10micro metre eliptical pore.
How does light affect stomatal opening?
Low light stimulates stomatal opening (especially blue light). CAM plants aren’t affected by this as they open nocturnally.
How does CO2 affect stomatal opening?
Low CO2 promotes opening.
How does Abscisic acid affect stomatal opening?
ABA is synthesised in the roots that are in dry soil which promotes stomatal closure.
