Transcript Plants that feed us

An Ecological Perspective
(BIOL 346)
Talk Six:
Plants That Feed Us
Plants that feed the world
• Hunger, starvation, and malnutrition are endemic in
many parts of the world today.
• Rapid increases in the world population have
intensified these problems!
• ALL of the food we eat comes either directly or
indirectly from plants.
• Can’t just grow more plants, land for cultivation has
geographic limits
– Also, can destroy ecosystems!
PlantsFigure
that 9.1
feed us
The Earth is currently experiencing
the most population increase in
Human
history.
2.5 billion in 1955 to 7 billion in 2012
At current rate, will double within
30 years!
Fastest growing nations have growth
rates at or above 4% - this will
double the countries population
every 17 years
Plants to feed the world
• At the latest count there are between 250,000 and
400,000 plant species on the earth.
• But three - maize, wheat and rice - and a few close
runners-up, have become the crops that feed the
world. All produce starch, helping to provide energy
and nutrition, and all can be stored.
• Maize converts the sun’s energy into sugar faster,
and potentially produces more grains, than any of
the other major staples.
Plant Starch (Amylose and Amylopectin)
•
Starch contains a mixture of amylose and amylopectin
•
Amylose is an unbranched polymer (forms -helix) of D-glucose molecules linked by 1,4-glycosidic bonds
•
Amylopectin is like amylose, but has extensive branching, with the branches using -1,6glycosidic bonds
What comes from plants
Popular stimulants like coffee, chocolate,
tobacco, and tea.
Simple derivatives of botanical natural products; for
example, aspirin is based on the pain killer salicylic
acid which originally came from the
bark of willow trees.
Most alcoholic beverages come from fermenting
plants such as barley (beer), rice (sake)
and grapes (wine).
What comes from plants
• Plants also provide us with many natural materials
– hemp, cotton, wood, paper, linen, vegetable oils, some types
of rope, and rubber.
• The production of silk would not be possible
without the cultivation of the mulberry plant.
• Sugarcane, rapeseed, soy and other plants with a
highly fermentable sugar or oil content have
recently been put to use as sources of biofuels,
which are important alternatives to fossil fuels
A few of the many medicinal plants
Plants to feed the world
• The term Green Revolution is
used to describe the
transformation of agriculture in
many developing nations that led
to significant increases in
agricultural production between
the 1940s and 1960s
• Scientists bred short plants that
converted the sun’s energy into
grain rather than stem, so
preventing the mass starvation in
the developing world predicted
before the 1960s, at a cost of
higher inputs from chemical
fertilizers and irrigation.
Plants to feed the world
• Disease-resistant wheat
varieties with high yield
potentials are now being
produced for a wide range of
global, environmental and
cultural conditions.
• The Green Revolution has had
major social and ecological
impacts, which have drawn
intense praise and equally
intense criticism.
Remember!!
• Agriculture has changed
dramatically, especially since the
end of World War II.
• Food and fiber productivity
soared due to new technologies,
mechanization, increased
chemical use, specialization and
government policies that favored
maximizing production.
• These changes allowed fewer
farmers with reduced labor
demands to produce the majority
of the food and fiber in the U.S.
Remember!
• Has had major social and
ecological impacts, which have
drawn intense praise and equally
intense criticism.
• In fact, many regions of the
world peaked in food production
in the period 1980 to 1995
• Are presently in decline, since
desertification and critical
water supplies have become
limiting factors in a number of
world regions.
Plant Basics
• Roots – absorb water from the soil as
well as many mineral nutrients
• Xylem – transports water from the
roots to the rest of the plant
• Phloem – transports sugars made in
the leaves via photosynthesis to the
pest of the plant
• Leaves – Site of gas exchange CO2
brought in and O2 out. Have
structures called Stomata which also
control water loss.
Plants and water
• Water is the essential medium of life.
• Land plants faced with dehydration by water loss to the
atmosphere
• There is a conflict between the need for water conservation
and the need for CO2 assimilation
– This determines much of the structure of land plants
– 1: extensive root system – to get water from soil
– 2: low resistance path way to get water to leaves – xylem
– 3: leaf cuticle – reduces evaporation
– 4: stomata – controls water loss and CO2 uptake
– 5: guard cells – control stomata.
Water across plant membranes
• There is some diffusion
of water directly across
the bi-lipid membrane.
• Auqaporins: Integral
membrane proteins that
form water selective
channels – allows water to
diffuse faster
– Facilitates water
movement in plants
• Alters the rate of water
flow across the plant cell
membrane – NOT
direction
Water transport in Plants
• Xylem:
– Main water-conducting tissue of
vascular plants.
– arise from individual cylindrical
cells oriented end to end.
– At maturity the end walls of
these cells dissolve away and
the cytoplasmic contents die.
– The result is the xylem
vessel, a continuous nonliving
duct.
– carry water and some dissolved
solutes, such as inorganic ions,
up the plant
Water and plant cells
• 80-90% of a growing plant cell is
water
–
–
–
–
This varies between types of plant cells
Carrot has 85-95% water
Wood has 35-75% water
Seeds have 5-15% water
• Plant continuously absorb and lose
water
– Lost through the leaves
• Called transpiration
Water
Water
• (A) Hydrogen bonds
between water
molecules results in
local aggregations of
water molecules
• (B) Theses are very
short lived, break up
rapidly to form more
random
configurations
• Due to temperature
variations in water
Photosynthesis
The (very) Basic facts
Photosynthesis
•Very little of the Sun’s
energy gets to the ground
gets absorbed by water
vapor in the atmosphere
•The absorbance spectra of
chlorophyll.
Absorbs strongly in the
blue and red portion of
the spectrum
Green light is reflected
and gives plants their
color.
•There are two pigments
•Chlorophyll A and B
General overall reaction
6 CO2 + 6 H2O
Carbon dioxide
Water
C6H12O6 + 6 O2
Carbohydrate
Oxygen
Photosynthetic organisms use solar energy to synthesize
carbon compounds that cannot be formed without the input
of energy.
More specifically, light energy drives the synthesis of
carbohydrates from carbon dioxide and water with the
generation of oxygen.
Overall Perspective
• Light reactions:
– Harvest light energy
– Convert light energy to
chemical energy
• Dark Reactions:
– Expend chemical energy
– Fix Carbon [convert CO2 to
organic form]
Photosynthetic pigments
• Two types in plants:
• Chlorophyll- a
• Chlorophyll –b
• Structure almost identical,
– Differ in the composition of a
sidechain
– In a it is -CH3, in b it is CHO
• The different sidegroups 'tune' the
absorption spectrum to slightly
different wavelengths
– light that is not significantly
absorbed by chlorophyll a, will
instead be captured by chlorophyll b
The chemical reaction of
photosynthesis is driven by light
• The initial reaction of
photosynthesis is:
– CO2 +H2O
(CH2O) + O2
– Under optimal conditions
(red light at 680 nm), the
photochemical yield is almost
100 %
– However, the efficiency of
converting light energy to
chemical energy is about 27
%
• Very high for an energy
conversion system
The Chloroplast
• Membranes contain chlophyll and
it’s associated proteins
– Site of photosynthesis
• Have inner & outer membranes
• 3rd membrane system
– Thylakoids
• Stack of Thylakoids = Granum
• Surrounded by Stroma
• During photosynthesis, ATP from
stroma provide the energy for the
production of sugar molecules
The light reactions
• Step 1 – chlorophyll in
vesicle membrane capture
light energy
• Step 2 – this energy is
used to split water into
2H and O.
• Step3 – O released to
atmosphere. Each H is
further split into H+ ion
and an electron (e-).
• Step 4 – H+ ion build up in
the stacked vesicle
membranes.
The light reactions
• Step 5 – The e- move down
a chain of electron
transport proteins that
are part of the vesicle
membrane.
• Step 6 – e- ultimately
delivered to the molecule
NADP+ - forming NADPH
• Step 7 - Some membrane
proteins pump H+ into the
interior space of the
vesicle
– Stored energy
• Step 8 – These make ATP!
Summary of light reactions
• Plants have two reaction centers:
– PS-II
• Absorbs Red light – 680mn
• makes strong reductant (& weak oxidant)
• oxidizes 2 H2O molecules to 4 electrons, 4 protons & 1
O2 molecule
• Mostly found in Granum
– PS-I
•
•
•
•
Absorbs Far-Red light – 700nm
strong oxidant (& weak reductant)
PS-I reduces NADP to NADPH
Mostly found in Stroma
The Carbon
reactions
• The NADPH and ATP move
into the liquid environment
of the Stroma.
• The NADPH provides H
and the ATP provides
energy to make glucose
from CO2.
• The Calvin cycle thus
fixes atmospheric CO2
into plant organic material.
Overview of the carbon reactions
• The Calvin cycle:
• The cycle runs six times:
– Each time incorporating a
new carbon . Those six
carbon dioxides are reduced
to glucose:
– Glucose can now serve as a
building block to make:
• polysaccharides
• other monosaccharides
• fats
• amino acids
• nucleotides
Photorespiration
• Occurs when the CO2 levels inside a leaf become low
•
– This happens on hot dry days when a plant is forced to close its
stomata to prevent excess water loss
• If the plant continues to attempt to fix CO2 when its stomata are
closed
– CO2 will get used up and the O2 ratio in the leaf will increase
relative to CO2 concentrations
• When the CO2 levels inside the leaf drop to around 50 ppm,
– Rubisco starts to combine O2 with Ribulose-1,5-bisphosphate
instead of CO2
The C4 carbon Cycle
• The C4 carbon Cycle occurs in 16 families of
both monocots and dicots.
– Millet
– Sugarcane
– Maize
• There are three variations of the basic C4
carbon Cycle
– Due to the different four carbon molecule
used
The C4 carbon Cycle
• This is a biochemical pathway that
prevents photorespiration
• C4 leaves have TWO chloroplast
containing cells
– Mesophyll cells
– Bundle sheath (deep in the leaf so
atmospheric oxygen cannot diffuse
easily to them)
• C3 plants only have Mesophyll
cells
• Operation of the C4 cycle requires the
coordinated effort of both cell types
– No mesophyll cells is more than
three cells away from a bundle
sheath cells
• Many plasmodesmata for
communication
Ah, the big hitters!
maize, wheat and rice
Maize (Corn)
• Represents the most
remarkable plant breeding
achievement in the history of
agriculture.
• The modern manifestation of
this ancient plant bears very
little resemblance to its original
ancestor, a wild grass from
southern Mexico called
teosinte.
Photo courtesy of Raúl Coronado
Maize
•
Teosinte is a tall, drought-tolerant
grass that produces, instead of a
cob, spikes close to the ground,
filled with two rows of small,
triangular-shaped seeds within an
enclosed husk
•
A hard shell around each seed
protects them once they fall to the
ground
•
This transformation from an
inconspicuous grass to a diverse,
highly evolved and productive food
plant spans thousands of years
•
A story of co-evolution and
interdependence between humans
and corn unprecedented in nature
Maize
•
100 years after discovering that teosinte
was edible, people began selecting spikes to
plant near their homes, which were close to
irrigation sources.
•
These selected plants continued to be
developed in isolation from wild teosinte
that was growing in the surrounding forests,
and thus the process of developing corn had
begun.
•
The difference between Teosinte and
maize is about 5 genes.
•
About 5 regions of the genome (which could
be single genes or groups of genes) seemed
to be controlling the most-significant
differences between teosinte and Maize
Maize
• The oldest known corncobs,
distinctly different from
teosinte, were found in the
highlands of Oaxaca in
southwestern Mexico and are
estimated to be 5,400 years
old.
•
Maize cobs uncovered by
archaeologists show the evolution
of modern maize over thousands
of years of selective breeding.
•
Even the oldest archaeological
samples bear an unmistakable
resemblance to modern maize.
•
About two-thirds of the maize grown
in the United States goes into
livestock feed.
Maize
– Hogs eat almost half the corn
crop.
•
Maize provides the base for many
kinds of poultry feeds and dairy
feeds.
•
Maize and cornstalks are also made
into silage, a fermented livestock
feed.
•
Americans eat about 45 pounds of
Maize per person per year.
•
Many kinds of food are made from
the kernels.
•
Maize also provides food indirectly,
in the form of the meat and meat
products that come from animals
raised on it.
Maize, in one form or another,
makes up more of our diet than
any other farm crop.
•
From: www.robinsonlibrary.com
Wheat
• Wheat originated in the “cradle of
civilization” in the Tigris and
Euphrates river valley, near what
is now Iraq and the Ethiopian
Highlands
• The Roman goddess, Ceres, who
was deemed protector of the
grain, gave grains their common
name today – “cereal.”
• Wheat is the primary grain used in
U.S. grain products —
approximately three-quarters of
all U.S. grain products are made
from wheat flour.
Six classes bring order to the thousands of varieties of wheat. They
are: hard red winter (HRW), hard red spring (HRS), soft red winter
(SRW), hard white (HW), soft white (SW) and durum.
Wheat Genetics
• Wheat genetics is more complicated than
that of most other domesticated species.
• Some wheat species are diploid, with two
sets
of
chromosomes.
Many
are
stable polyploids, with four sets of
chromosomes (tetraploid) or six (hexaploid).
• Genes for the 'dwarfing' trait, first used
by Japanese wheat breeders to produce
short-stalked wheat, have had a huge
effect on wheat yields world-wide.
• Dwarfing genes enable the carbon that is
fixed in the plant during photosynthesis to
be diverted towards seed production.
Wheat
• Became known as Norin 10
• This grows to just two feet tall, instead of
the usual four, which made it less prone to
wind damage.
– Other varieties grow too high, become
top-heavy, and lodge
• By 1997, 81% of the developing world's
wheat area was planted to semi-dwarf
wheats, giving both increased yields and
better response to nitrogenous fertilizer.
• Norin 10 helped developing countries,
such as India and Pakistan, to increase
the productivity of their crops from
approximately 60% during the Green
Revolution.
Rice
• This is the seed of the monocot
plants Oryza sativa (Asian rice)
or Oryza glaberrima (African rice).
• Rice is the most important grain
with regard to human nutrition and
caloric intake, providing more than
one fifth of the calories consumed
worldwide by humans.
• Genetic evidence has shown that
rice originates from a single
domestication 8,200–13,500 years
ago, in the Pearl River valley
region of China.
•
Where is rice grown?
•
Rice is grown in eight American
States
•
Arkansas
•
California
•
Texas
•
Louisiana
•
Minnesota
•
Mississippi
•
Missouri
•
Florida
From the Rice knowledge Bank
Rice
•
Rice cultivation is well-suited to countries
and regions with low labor costs and high
rainfall, as it is labor-intensive to cultivate
and requires ample water.
– Rice can be grown practically anywhere,
even on a steep hill or mountain.
• The traditional method for cultivating
rice is flooding the fields while, or
after, setting the young seedlings.
• This simple method requires sound
planning and servicing of the water
damming and channeling, but reduces
the growth of less robust weed and
pest plants that have no submerged
growth state, and deters vermin and
many pathogens.
Rice Environmental impacts
• Rice cultivation on wetland rice fields is thought to be responsible for
6–21% of the annual methane emissions produced via Human interaction
with the environment.
– The Long-term flooding of rice fields cuts the soil off from atmospheric
oxygen and causes anaerobic fermentation of organic matter in the soil.
• Rice requires slightly more water to produce than other grains.
• As a result of rising temperatures and decreasing solar radiation during
the later years of the 20th century, the rice yield growth rate has
decreased in many parts of Asia.
• The reason for this falling yield is not fully understood
– might involve increased respiration during warm nights, which expends
energy without being able to photosynthesize
The End.
Any Questions?