G3p is the product of the calvin cycle and is used by

G3P is the product of the Calvin Cycle and is used by the plant to make:
•
Sucrose
•
Fructose
•
Starch
•
Cellulose
•
use the hydrocarbon skeleton of G3P to form fatty
acids and glycerol (corn oil, olive oil)

http://
/departments/Biology/Bio231/ calvin.html

C
3
plants
• Use CO
2
directly from the air .
•
Very common and widely distributed.
•
Example : Wheat, rice, oats, tulips

Efficient under:
•
cool and moist conditions
•
normal light
Requires less machinery:
•
fewer enzymes
•
no specialized anatomy
C
3
plants
Adaptive Value

C
4
plants
•
Close stomata during the day to save water
during hot and dry weather.
•
Great!
•
Water kept inside leaf
•
Problem!
•
O
2
as well,
•
can bind to Rubisco competing with
CO
2
•
Alternate mode of carbon fixation
resulting in a 4-carbon product
unique leaf anatomy with 2 distinct types of
photosynthetic cells: bundle-sheath cells
and mesophyll cells
Example : corn, sugarcane

1. CO
2
first fixed and kept in a 4
Carbon molecule (malate) in
mesophyll cells (surface of leaf)
•
contain lots of atm O
2
but
NO RUBISCO
2. Malate delivered to bundle sheat
cells (deeper inside leaf) and
converted back into a 3 carbon sugar
called pyruvate
•
less O
2
•
Liberation of CO
2
which
enters Calvin cycle
C
4
plants
Bundle-
sheath
cell
Pyruvate (3 C)
CO
2
Sugar
Vascular
tissue
CALVIN
CYCLE
PEP (3 C)
ATP
ADP
Malate (4 C)
Oxaloacetate
CO
2 PEP carboxylase
Mesophyll cell

C
3
vs C
4
• Moderate weather, advantage to C
3
plants
•
But when the weather becomes hot and dry,
advantage to C
4
plant
–
Early summer,
• C
3
plants, Kentucky bluegrass,
predominate in lawns in cooler parts of
US,
– By midsummer,
• crabgrass, a C
4
plant, begins to take
over

CAM plants
•
Open stomata only at night :
•
conserve water,
1. CO
2
taken up at night
when stomata are open
and incorporated into a 4-
C organic acids through
the crassulacean acid
metabolic (CAM)
pathway
2. Organic acid kept in
vacuole until next day’s
sun energy when light
reactions can be carried
out (makes ATP and
NADPH)
CO
2
released and enters
Calvin Cycle
Bundle-
sheath
cell
Mesophyll
cell
Organic acid
C
4
CO
2
CO
2
CALVIN
CYCLE
Sugarcane Pineapple
Organic acids
release CO
2
to
Calvin cycle
CO
2
incorporated
into four-carbon
organic acids
(carbon fixation)
Organic acid
CAM
CO
2
CO
2
CALVIN
CYCLE
Sugar
Spatial separation
of steps
Temporal
separation of steps
Sugar
Day
Night