Transcript ppt11 - Plant Agriculture

AGR2451 Lecture 11 - M. Raizada
“Using and Storing Plant Carbon”
1. Photosynthesis results in high energy cofactors (ATP/NADPH)
to allow chemical reactions to occur (via enzymes encoded by
genes).
2. The Calvin Cycle uses these cofactors to remove C from CO2,
add it to a 5C acceptor, to build 2x3C and regenerate 5C.
3. Carbon-fixation from CO2 occurs via RuBisCo, the most
abundant and perhaps slowest enzyme known.
4. O2 competes with CO2 for binding to RuBisCo.
QUESTIONS??
------------------------------------------------------------------------5. 3C is produced in the chloroplast. The initial 3C can be
broken down to a very reactive 2C (acetyl Co-A) or can form
the 6C glucose subunit in the cytoplasm.
What are the 4 major fates of the 3C molecule? (see handout):
Slide 11.1
What are the 4 major fates of the 3C molecule? (see handout):
Need
What happens?
Immediate
energy
(same cell)
-6C broken down to 3C
via glycolysis
-3C metabolized to 2C
in mitochondrion
-2C broken down to
CO2 (respiration)
Where?
Need fatty
acids, amino
acids, etc.
Store energy
(same cell)
Energy or
subunits
needed
elsewhere
-6C + 6C = sucrose =
transport form of carbon
-phloem
-stored in organelles
(fats/oils, starch) or used
Slide 11.2
6. Glucose (6C)
glucose is a temporary storage form for C-C bonds.
7. Sucrose (12C)
The transport form of C-C in a plant is typically 12C
(ie.sucrose), transported in the phloem. This is why the sap of
the trunk of a Maple tree is sweet or why the stalks of sugarcane
are sweet.
8. Storage Compounds
For long-term storage, long chains of C-C bonds are formed as
fats/oils, or starches. Long carbon chains are very stable and
unreactive especially fats/oils stored in seeds (high in calories),
stored in specialized oil body organelles.
Why is carbon stored in long chains (starches/oils) instead of
simpler subunits (such as glucose)?
Slide 11.3
9. Plant Cell Walls
Glucose subunits joined together by a large enzyme complex
on the outside of the plasma membrane.
Cellulose microfibres
P.648 and p.659
Biochemistry and Molecular Biology of Plants
Construction of
Cellulose cell wall
Slide 11.4
10. Plant Structure vs. Metabolic Function
NEED
ORGAN/STRUCTURE
CO2
stomates
O2
Stomates
H20
Acquisition - ________
Transport- _________
Transpiration/loss - _________
Organ transport - ________
Vascular tissue -_________
Sunlight
capture
Chloroplast, flat leaves,
Leaf phyllot axy,
determinate/indeterminate growth
Chains of 6C
glucose
Cellulos e - cell walls
Starch (leaves/roots)
Aid young - _____________
_____________
Amylopl ast organelles
Chains of 2C
membranes for compartments
oils , fats, in seeds or pollen
oil bodies
Transport - _________
Herbivore attraction - _______
Vascular tissues (in leaves, roots)
for transport
12C sucrose
Draw Plant
*** In breeding or during evolution, the needs of primary
metabolism (carbon fixation, etc.) drove plant development, not
the other way around. Structures exist for carbon/nitrogen/H20.
Carbon metabolism, alone, explains much of the plant structure.
Slide 11.5
11. Energy may be stored in the cell walls of leaf cells,in the roots,
not just seeds/fruits. Grazing livestock mostly feed, not on seeds,
but on the cell walls of leaves. Thus, it is important to view the
entire plant as a nutrient-storage organism.
12. Carbon Partitioning
Carbon reserves may be remobilized when the plant has a need
(eg. grain-fill) or to any growing organ.
What are some of the primary carbon “sinks”?
1.
2.
3.
4.
5.
Therefore, the control of carbon transport or “partitioning” of
carbon to these sinks is critical to agriculture and breeding.
eg. vegetative growth vs. seeds.
Harvest Index?? ____________________________________
-Up to 30-40% of fixed carbon is transported to the roots, some of
It excreted into the soil for use by microbes/fungi.
13. Gross productivity?? ______________________________
-40-80% of photosynthate is lost in respiration or photorespiration
-There has been ~no change in Gross Productivity after 10,000
years of human selection! Breeding has simply allowed the carbon
to be partitioned to edible organs, increasing the Harvest Index.
Slide 11.6
14. How efficient is the transfer of plant carbon to humans?
25-70% of plant carbon lost as respiration, 30-60% is
undigestable, leaving up to 2-15% for insects and herbivores.
QuickTime™ and a
Photo - JP EG decompressor
are needed to see this picture.
Plants, Genes and Agriculture,pp.183
M. Chrispeels and D.Sadava
Jones and Bartlett Publishers, Boston, 1994
Starting with ________ calories of sunlight in an alfalfa field,
_____ calories are produced as hay for cow feed, resulting in
____calories of cow matter, producing __ calorie of human matter.
•In natural ecosystems, 0.2 to 3.5% of incident light energy is
converted into dry matter =net productivity. This can be as high
as 4% in agricultural C4 crops such as maize and sugarcane
•Through animal chain, up to 90% of plant calories are lost due to
respiration or undigested material: chickens (75% lost) but less
For beef (4-6 kg plant protein = 1 kg beef).
Slide 11.7
15. What ratio of storage molecules do plants produce?
Plant Dry Weight:
•44% = Carbon (44% is oxygen, 6% is hydrogen, 1-4% is N,
0.5-6% is Potassium, 0.2-3.5% is Calcium, and P, Mg and S
are each less than 1%)
-59% of leaf dry weight = carbohydrates, 6% are lipids, 19%
are proteins, 9% are minerals and 7% are others. Corn seeds
have higher lipids (oils).
What constitutes 50% of the leaf protein? _______
Breeding programs alter carbohydrate/sugar/fat and protein
ratios, especially in seeds.
16. What ratio of carbon storage molecules do humans
consume?
Plants, Genes and Agriculture,pp.111
M. Chrispeels and D.Sadava
Jones and Bartlett Publishers, Boston, 1994
QuickTime™ and a
Photo - JPEG decompressor
are needed to see this picture.
118
16. Today, plant storage carbon is being manipulated for
human health, for renewable industrial products and energy.
•possible improvement is to develop monounsaturated soils that may
reduce risk of heart attacks and strokes:
•Canola is a mutation in a gene of Brassica napus (rapeseed) that
decreased a monosaturated fatty acid (22:1) called Erucic acid which
constituted 50% of the oil but caused heart disease
•much work on developing better oils for animal feed
•fatty acids can be used to produce nylon, plastics, lubricants, soaps,
paints, detergents, adhesives, and perhaps biofuels
-ethanol/methanol from corn (current car gasoline is largely from
ancient plants)
•oil found in distinct oil bodies in plant cells
•breeding and genetic engineering can produce novel materials
Examples
•demo -- biodegradeable foam packing chips (starch)
•plastic granules produced in plants (in Arabidopsis)using a transgene
from bacteria = biodegradeable plastic
QuickTime™ and a
PNG decompressor
are needed to see this picture.
Figures 1 and Figure 3 from:
Biochemistry and Molecular Biology of Plants
(W.Gruissem, B. Buchanan and R.Jones p.525
ASPP, Rockville MD, 2000
Slide 11.9