Transcript CAM photosynthetic pathway

Rangeland Plant Ecophysiology
Wednesday, September 16, 2009
Crassulacean Acid Metabolism
CAM physiology, biochemistry, anatomy
Ecology of CAM plants
Phylogenetics and biogeographic distribution
CAM idling
CAM cycling
Facultative CAM
Aquatic CAM plants?
C4
photosynthetic
pathway
ADP
ATP
8.14 Crassulacean acid metabolism (CAM) (Part 1)
1. Starch is degraded at night to
form PEP, a 3-carbon
compound.
2. PEP combines with HCO3(hydrated CO2 from atm).
Reaction is catalyzed by
PEP-carboxylase.
3. The 4-carbon acid (OAA) is
converted to Malate where it
is actively (ATP) pumped into
vacuole and stored as malic
acid.
4. Acidity (and malic acid
concentration) of vacuole
builds up at night as reaction
proceeds.
8.14 Crassulacean acid metabolism (CAM) (Part 2)
1. The next morning,
stomates close, and malic
acid is transported out of
vacuole and
decarboxylated to
Pyruvate.
2. CO2 concentration builds
inside tissues where it
diffuses to chloroplasts to
be assimilated by Rubisco
in Calvin cycle.
3. Some of the starch that is
built up during day is
converted at night to PEP.
Taiz and Zeiger, Figure 9.24 – CAM gas exchange
CAM is an adaptation to drought!
Epiphytes in Trinidad
Water-use efficiency (WUE)
Amount of water loss per
amount of CO2 gain
(g H2O / g CO2)
Fick’s law
(Don’t forget it!)
Facultative CAM
Example:
Ice plant
(Mesembryanthum crystallinum)
Another facultative CAM
Agave deserti
of the Sonoran desert
Some submerged aquatic plants
(e.g., Isoetes) have evolved the
CAM photosynthetic pathway.
WHY?
Terms to know:
CAM – Crassulacean Acid Metabolism photosynthetic pathway
malic acid
vacuole
succulence
Water-use efficiency in CAM plants
CAM idling
CAM cycling
facultative CAM
aquatic CAM plants