Transcript Unit A2-8

Understanding Plant Growth
Regulators
What is a Plant Growth
Regulator?

Chemicals which affect the plant in
many complex ways

Cell division and differentiation, root and
shoot growth, flowering and ripening
2 Types of Plant Growth Regulators
Natural
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Made inside the
plant
Low concentrations
Five groups
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Auxins, cytokinins,
ethylene, gibberellins
and abscisic acid
Man-made/Synthetic

Applied to plants to
obtain a wide variety
of changes

Makes the plant
better or more
saleable!
Which grapes would you
rather eat?
The ones on the right
were treated with
gibberellic acid to make
them larger.
Naturally Made Plant Hormones
Auxins
Produced by the tip, or
apical meristem


Stem cells elongate
and divide
They also flow down
from the tip of the
stem, preventing
lateral buds blooming
early
3 Effects of Auxin on Plants
This trunk
should be a
single stem;
however, the
terminal bud
was removed
forcing it to
branch.

1. Auxin causes the tip
of the middle stem to
grow at a faster rate

2. Auxins are
responsible for allowing
a plant stem to grow
toward the sun
The left side of the plant was
exposed to the sun. The right
side had shade and grew
faster.

3. Auxins allow a plant to
respond to the touch of a
person or other object
Cytokinins

Responsible for cell
division and
differentiation

Produced in the root
tips
They tend to travel
up the stem

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Effect is Apical
Dominance
Ethylene
This is a gas that affects the plant like a
hormone


It is produced in ripening fruit and dying plant
material
It stimulates flowering in some plants and
causes other fruits and flowers to ripen more
quickly and evenly
Effects of Ethylene


Ripen fruits faster in a
paper bag, than on the
counter
On cut flowers & foliage will
die
In this experiment, two holly twigs
were placed under separate jars
for a week. At the same time, an
apple was placed in the second
jar. The ethylene given off by the
apple caused the holly to lose its
leaves and die.
Gibberellins

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Helps promotes growth and stem
elongation for trees
Produced in the stems, roots and young
leaves
Effects are flowering of plants early and
breaking seed dormancy too soon
Abscisic Acid (ABS Acid)

Found in dormant
seeds and in dying
leaves

Effects are inhibiting
growth and induced
bud dormancy
Helps a plant
prepare its buds for
winter

The dormant bud on the left has a
high concentration of abscisic acid.
As spring nears, the acid level drops
and the bud begins to develop a new
shoot.
Synthetic Plant Growth Regulators
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Useful for commercial plant crops
They can save money, time, and can lead to a
better crop

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Help reduce size and make plant look shorter
Root more completely
Help ripen faster
Assignment
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You and a partner will make up a poem/
song/riddle/ect about natural and
synthetic plant growth regulators.
You must have the following:
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Auxins, cytokinins, ethylene, ABS acid, and
Gibberlines
What they do to the plant
Be creative and appropriate
You will present to the class your
poem/song/riddle