Transcript I Wish You Enough - Labs - Department of Plant Biology, Cornell

Red White and Blue Tortilla Chips
The Domestication of Maize
Physiology of Plants
Randy Wayne
Shoals Marine Lab
July, 2009
Life: The Ability to Respond Appropriately to
the Environment
Consciousness, as
defined as an awareness
of the external
environment—the first
step in responding
appropriately to the
environment, is a
characteristic of life and
may have begun with the
first cell.
Plants Sense and Respond to the
Environment
If we were to walk
quietly and observantly
through a garden at the
Cornell Plantations, it
would become
increasingly clear that it
is a normal and
ubiquitous property of
plants to sense and
respond to their
environment.
http://www.plantations.cornell.edu/
Plants Sense and Respond to the
Environment: Phototropism
Plants sense the direction of light and bend or
turn toward the light.
Plants Sense and Respond to the
Environment: Gravitropism
Plants sense the
vector of gravity
and the shoots bend
up; away from the
source of the
gravitational force,
and the roots bend
down; toward the
source of the
gravitational force.
Plants Sense and Respond to the
Environment: Thigmotropism
Plants, particularly vines, have a sense of touch. When the
tendrils come in contact with a support, they quickly respond
to the mechanical force and curl around the support. Thigmo
is the Greek word for touch.
Venus’ Fly Traps Can Sense Touch,
Capture Their Prey, Secrete
Digestive Enzymes and Absorb the
Nitrogenous Nutrients
Mimosa Can Sense Touch and Heat
Plants Sense and Respond to the
Environment: Photoperiodism
Plants sense day
length (or really the
length of the night)
so that they can flower
in the spring or fall,
when the days are
short, or in the
summer, when the
days are long.
Circadian
(about a day)
Rhythms
Plants sense the
duration of time
and move their
leaves throughout
a 24 h cycle.
http://plantsinmotion.bio.indiana.edu/redirect.html
The Living World is But Mankind in
the Making
Raoul Francé (1905)
wrote, “What grander
lesson could the speechless
plants give than that which
they have taught us: that
their sense life is a primitive
form, the beginning of the
human mind... it tells us
that after all the living
world is but mankind in
the making, and that we
are but a part of all.”
Germination of Lettuce Seeds
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Seeds have a variety of requirements that ensure that they germinate
in the right place and the right time.
Lettuce seeds need a pulse of red light (660 nm) to germinate.
If the red light is immediately followed by a pulse of far-red light
(730 nm), the seeds no longer germinate.
The photoreceptor the senses the quality of the light is called
phytochrome (plant color).
Germination of Lettuce Seeds
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The seeds can be exposed to many rounds of red and far-red
pulses, but it is only the last pulse that matters in inducing
germination.
Harry Borthwick and Sterling Hendricks concluded that
phytochrome acts like a switch. Light causes the
interconversion between the red absorbing form (Pr) and
the far-red absorbing form (Pfr). Only the far red absorbing
form causes germination.
Phytochrome
Pr
Pfr
Pfr
Pr
Phototropism: Discovery of the Site of
Perception
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Charles and Francis Darwin found that coleoptile bent toward blue
light and the apex is required for the phototropic response even though
the bending takes place below the tip.
They concluded that the tip of the coleoptile sensed the light and then
some “influence” traveled from the tip to the bending zone.
Phototropism: Discovery of the
Chemical Nature of the Stimulus
In order to test the possibility that a hormone was produced by the tip
and transported down to the growing zone, Peter Boysen-Jensen
inserted a piece of mica in order to block the transport of the hormone
and showed that transport of the hormone toward the base occurs on
the dark side of the plant as opposed to the side exposed to the
unidirectional light.
Phototropism
Paal cut off coleoptile tips in the dark and exposed the tips to
light. Then he replaced the tip on the plant but off centered to
one side or the other.
He found that the coleoptile curved away from the side that
was exposed to the tip.
Phototropism
Frits Went figured that if the influence was a hormone, he
could trap it in a block of agar and then put it asymmetrically
on the coleoptile and induce curvature in the dark. It worked!
Went named the hormone auxin, which means “to grow.”
Humans Eat Plants, and Human Urine
Causes Coleoptiles to Bend
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Urine has traditionally been a convenient (and cheap) source
for the isolation of chemicals (e.g. guanine and other
purines).
F. Kogl and A. J. Haagen-Smit first isolated auxin from
human urine in 1931.
Soon Auxin was Isolated From Plants
Too!
Winslow Briggs Showed that blue light causes
bending in coleoptiles by causing a redistribution
of auxin from the lighter side to the darker side.
Added Auxin Causes Coleoptiles to
Elongate
The Mechanism of Phototropism
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Blue light induces
bending by causing a
lateral redistribution
of the hormone auxin
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from the lighted side of
the tip to the dark side.
The increased auxin
on the dark side
stimulates elongation,
which results in bending
toward the light.
How Auxin May Induce Long Term Growth
Ethylene and Aging Responses
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In the 1880s, after the
installation of coal gas lamps,
people began to notice that
leaves dropped off the
plants that were exposed to
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gas leaks.
In 1910, H. H. Cousins noticed
that rotten oranges caused the
premature ripening of
bananas and ethylene
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produced by the oranges was
the cause of ripening.
In 1934, R. Gane classified
Ethylene Promotes Senescence
(Aging) of Many Flowers
• Older flowers produce ethylene.
• The ethylene promotes the
senescence of flowers, which
has evolved to rid the plant of
older flowers that have most
likely been pollinated so that
the young not-yet-pollinated
flowers have a better chance of
being pollinated.
• This is good for the plant, but
not for people who like flowers
in their home.
Ethylene Promotes Ripening (Aging) of
Many Fruits
Ripening, which has evolved to promote fruit
dispersal, involves the synthesis of sugars, the
degradation of cell walls to make the fruits softer
and the production of chemicals that provide color,
flavors and aromas.
Ethylene Antagonists Prevent Aging
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1-MCP (1 methyl
cyclopropene; C4H6),
an ethylene (C2H4)
antagonist prevents
flower senescence and
further fruit ripening.
1-MCP binds tightly
to the ethylene
receptor thereby
blocking the effects of
ethylene.
Abscission
Roles of Ethylene and Auxin during
Abscission
Healthy leaves, flowers
and fruits produce
auxin, which is
transported down
toward the stem. The
cells in the region of
the petiole known as
the abscission zone are
insensitive to
ethylene.
In response to age,
touch or day length,
the amount of auxin
produced by the organ
decreases. When the
level of auxin drops,
cells in the abscission
zone become sensitive
to ethylene.
The increase in
ethylene activates the
enzymes that digest the
cell walls in the
abscission zone, and
the weakened organ
falls.
Synthetic Auxins Cause Defoliation
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While Art Galston (1943) was looking
for a chemical means to make soybeans
flower and fruit earlier so that they could
thrive in regions with a short growing
season, he discovered that a low
concentration of a synthetic auxin
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2,4,5-triiodoacetic acid) would speed up
flowing.
He also noticed that higher
concentrations were not good for
speeding up flowering even more
because higher concentrations caused
the leaves to fall off.
Cornell Alumnus, The
“price was right.”
Defoliation
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The army was interested in
the ability of 2,4,5-T to
defoliate jungle plants in
Viet Nam so that the Viet
Cong would have nowhere
to hide.
The army mixed 2,4,5-T
with two other synthetic
auxins to make Agent
Orange.
Agent Orange
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The herbicide mixture was named Agent Orange after the
color of the stripes on the 55 gallon drums it came in.
Agent Orange contained dioxin, a byproduct of 2,4,5-T
manufacture, which was a well known carcinogen.
Dioxin Increases the Risk for:
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D1. Birth Defects (Spina bifida and
Anencephaly)
D2. Chloracne
D3. Non-Hodgkin’s Lymphoma
D4. Soft Tissue Sarcomas
D5. Peripheral Neuropathy
D6. Hodgkin’s Disease
D7. Porphyria Cutanea Tarda
D8. Multiple Myeloma
D9. Respiratory Cancers
D10. Prostate Cancer
D11. Spina Bifida
D12. Diabetes
D13. Chronic Lymphocytic Leukemia
Spina bifida and Anencephaly
Bioethics
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In 2003, Dr. Galston reconsidered the
arc of his research.
“You know,” he said, “nothing that
you do in science is guaranteed to
result in benefits for mankind. Any
discovery, I believe, is morally
neutral and it can be turned either
to constructive ends or destructive
ends.”
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He concluded: “That’s not the fault of
science.” (Obituary in NYT June 23,
2008).
Archibald V. Hill
“It is true that scientific research has
opened up the possibility of
unprecedented good, or unlimited harm,
for mankind; but the use that is made
of it depends in the end on the moral
judgments of the whole community of
men. It is totally impossible now to
reverse the process of discovery: it will
certainly go on. To help guide its
use aright is not a scientific
dilemma, but the honourable
and compelling duty of a
good citizen.”
Erwin Chargaff
• The goal of science has changed
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from exploration and explanation
(knowledge) to exploitation
(intellectual property and profit).
“What I have called the change in
the moral climate is 1) that the
majority [of scientists] seem
to agree that what can be done
must be done…”
The Reaction of Scientific Progress
Upon Human Life and Thought
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You are a shareholder in the
world and have its future in
your hands.
Although it is often stated
that demand creates supply,
it is often the other way
around, supply creates
demand.
When science produces
something, people will buy
it.
Aldous Huxley
What do You Value about being Human?
• How do you measure the value
of being human?
• Are you willing to cede your
input on this question to
biotechnologists using a
business model to do science?
• Are you willing to take the time
to maintain and sharpen your
knowledge of biology in order to
make informed, knowledgeable
and wise personal, athletic,
business and political decisions
that reflect your values about
the value of being human?
http://www.hgalert.org/
I Wish You Enough
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I wish you enough sun to keep your attitude bright no
matter how gray the day may appear.
I wish you enough rain to appreciate the sun even
more.
I wish you enough happiness to keep your spirit alive
and everlasting.
I wish you enough pain so that even the smallest of
joys in life may appear bigger.
I wish you enough gain to satisfy your wanting.
I wish you enough loss to appreciate all that you
possess.
I wish you enough hellos to get you through the final
good-bye.
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