AGR2451 Lecture 11 - M. Raizada

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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?? ------------
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----------- 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)
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What are the 4 major fates of the 3C molecule?
(see handout)
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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)?
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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
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10. Plant Structure vs. Metabolic Function
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.
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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.
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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.
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).

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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
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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 (221)
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
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
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