Ashley Chandler

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Chapter 32!
Plant Responses and the Regulation of Growth

• Ashley Chandler
• P-2

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Introduction
The capacity to respond to stimuli is one of the
essential properties of all living
organisms. Plants are able to react to immediate
environmental stimuli, and they can also
anticipate environmental changes and prepare for
them. Many plant responses are slower than
animal responses, but they are no less
significant.
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Phototropism and the Discovery of Plant Hormones!
Im so excited!
A tropism is a growth response that involves the
curvature of a plant toward or away from an
external stimulus that determines the direction
of movement. . Toward stimulus positive .
Away from stimulus negative Phototropism! .
The curvature toward light . Charles Darwin and
son Francis determined curvature occurs below the
tip, in the lower part of the Celeoptile (hollow
sheath that surrounds the shoot tip)
.Celeoptile functions by chemical stimulus
(auxin)
http//www.atpm.com/6.09/montgomery/images/cayman-
sun.jpg
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Hormones and The Regulation of Plant Growth
Hormone a chemical substance that is produced in
one tissue and transported to another, where it
exerts one or more highly specific effects.
Hormones integrate the growth, development, and
metabolic activities of the various tissues of
the plant.
Hormones have inhibitory effects.
Consider them as chemical regulators.
Five principal types of plant hormones auxins,
cytokinins, ethylene, abscisic acid, and
gibberellins.
Ogliosacharins too!
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Auxin

• IAA
• Synthesized by the enzymatic conversion of the
  amino acid tryptophan.
• Produced by the apical meristem of the shoots.
• Causes cells in growing region of shoot to
  elongate. (Relatively rapidly)
• Also required for root growth.
• Stimulates long-term growth.
• Calcium ion is intimately involved in the effects
  of auxin on growth.
• Auxin induces an increase in amount of the
  Calcium ion, which activates calmodulin.
• Calmodulin affects membrane permeability,
  hydrogen ion transport, and activity of enzymes.

http//www.plant-hormones.info/auxins.htm
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Apical Dominance and Other Auxin Effects! WOOHOO!
Apical dominance When the growth of auxillary
buds is inhibited by auxin.
If you cut off the growing tip (apical meristem)
the axillary buds begin to grow vigorously. This
makes the plant bushier.
Effects are indirect on apical dominance.
Auxin stimulates production of ethylene, which
inhibits bud growth.
Auxin plays a role in seasonal initiation Of
activity in the vascular cambium.
http//koning.ecsu.ctstateu.edu/apical/apical.html
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CYTOKININS!
? Coconut.
Stimulate cell division.
First detected in coconut milk.
Most active naturally occurring cytokinin is
zeatin, originally isolated from corn.
Cytokinins resemble purine adenine.
Promote cell division.
Increase the rate of protein synthesis.
www.johnssketchpad.com/.../ coconut.jpg
http//users.rcn.com/jkimball.ma.ultranet/BiologyP
ages/C/Cytokinins.html
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RESPONSES TO CYTOKININS AND AUXIN COMBINATIONS!

• - Equal concentrations of auxin and cytokinin
  undifferentiated cells, form a mass called a
  callus.
• Higher concentration of auxin undifferentiated
  tissue gives rise to organized roots.
• Higher concentration of kinetin buds appear.
• Calcium ions can shift the growth pattern from
  cell enlargement to cell division.

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Other Cytokinin Effects
Reverse inhibitory effect of auxin in apical
dominance.
Preventing the senescence (aging) of leaves.
www-ang.kfunigraz.ac.at/.../ engl/Laur_nob.html
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ETHYLENE!
I was searching for pictures on Google, and I
just thought this was the funniest freaking thing
evera hamster with a microphone.
aggie.kps.ku.ac.th/ relax/relax-head.html

• A hormone that is a gas, a simple hydrocarbon.
• Speeds the ripening process.

• Ethylene-synthesizing system located on the cell
  membrane, from which the hormone is released.
• Responsible for changes in color, texture, and
  chemical composition.
• Thought to be an effector of apical dominance.
• Auxin induces ethylene production in or near
  auxillary buds.

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Ethylene and Leaf Abscission!

• Abscission when plants drop their leaves at
  regular intervals, either as a result of normal
  aging or in response to environmental cues.
• Preceded by changes in the abscission zone,
  located at the base of the petiole.
• Ethylene produced in the abscission layer is the
  principal regulator of leaf drop.
• Ethylene acts by promoting the synthesis and
  release of cellulase.
• Auxin inhibits abscission if applied to the leaf
  before senescence begins, but once the abscission
  layer is formed auxin promotes abscission by
  stimulating ethylene production.

www.lima.ohio-state.edu/ biology/leaves.html
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Abscisic Acid!
Once called Dormin, induces dormancy. Presents
in seeds of many species, has major factors in
seed dormancy. Brings about the closing of the
stomata under conditions of water shortage.
Stress hormone, protector of the plant against
unfavorable environmental conditions.
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Gibberellins! Discovered from foolish seedling
disease. More than 70 gibberellins are now
known. Giberellin and auxin control elongation in
mature trees and shrubs. Can cause
hyperelongation as in foolish seedling disease
Can produce bolting, flower stem elongates
rapidly. Can also induce cell differentiation.
Phloem and Xylem develop in the presence of
Gibberellins and auxins.
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Gibberellins and Seed Germination
Highest concentrations of gibberellins have been
found in immature seeds. In grains, there is a
specialized layer of cells, the aleurone layer,
just inside the seed coat. During early stages
of germination the embryo produces gibberellin,
which diffuses to the aleurone layer. Aleurone
cells then produce and release enzymes that
hydrolyze starch, lipids, and proteins in the
endosperm, converting them to sugars, fatty
acids, and amino acids that the embryo and
seedling can use.
www.sspictures.fsnet.co.uk/ gindb.htm
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Oligosaccharins
. A short chain of Sugar molecules.
Released from the plant cell wall.
Send out messages, basically, to tell when a
plant may be under attack from a pathogen.
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GRAVITROPISM
A plants response to gravity. Gravitropism is
thought to involve auxin. Increase in amounts of
Calcium ions inhibits growth along the upper
side, while auxin stimulates cells on the lower
side.
botit.botany.wisc.edu16080/ images/130/Extern...
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Photoperiodism

• Measuring periods of light and darkness.
• Plants are of three general types day-neutral,
  short-day, and long-day.
• Day-neutral flower without regard to day length.
• Short-day plants flower in early spring or fall.
• Long-day plants flower chiefly in summer, and
  flower only if light periods are longer than
  critical length.
• Plants actually measure the amount of darkness.

...and flowering
www.xanga.com/home. aspx?userlilystar222
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Photoperiodism and Phytochrome
The pigment phytochrome exists in two different
forms. Pr, and Pfr. Pr absorbs red light, with
a wavelength of 660 nanometers. Pfr absorbs
far-red light with a wavelength of 730
nanometers. When Pr absorbs light is is
converted to Pfr.
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Other Phytochrome Responses Phytchrome is
involved in the early development of seedlings.
Phytochrome is also involved in the switching
from etoilated to normal growth. An increase in
the concentration of all the growth-promoting
hormones can be detected almost immediately after
phytochrome division.
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Circadian Rhythms
Photosynthesis, auxin production, and the rate of
cell division have daily rhythms. These regulare
day-night cycles are called circadian rhythms.
Biological Clocks
Circadian rhythms are endogenous, they originate
within the organism. The mechanism by which they
are controlled is a biological clock. Biological
clocks synchronize internal and external events.
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www.creativewatch.co.uk/ radio-controlled-watc...
Resetting the Clock Circadian rhythms can be
modified by external conditions, which is
important in keeping organisms in tune with their
environment. Entrainment an adjustment to an
externally imposed rhythm. Organisms will revert
to their natural rhythm. The Nature of
Clockwork On/off switch Phytochrome Timing
mechanism involves rhythmic changes in the cell
membrane, either in protein components,
phospholipids, or both. Phytochrome conversion
resets the clock by producing changes in membrane
structure or permeability.
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www.metabug.dyndns.org/.../ slides/Vines.html
Touch Responses

• Twining and Coiling
• Many plants respond to touch.
• Most common example is tendrils, modified stems
  or leaves with which many plants support
  themselves and climb.
• Tendrils often move in a spiral.
• Cells touching the support shrink slightly, and
  those on the outer side elongate.
• Coiling requires light for ATP production.

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Rapid movements in the Sensitive Plant Rapid
response is a result of sudden change in turgor
in specialized motor cells of joint-like
thickenings called pulvini at the base of the
leaflets and leaves. A single leaf or all the
leaves may be effected depending on the variety
and the stimulus. The sensory stimulus is
apparently rapidly translated into an electrical
signal, similar to a nerve impulse in animals.
The electrical signal, in turn, triggers a
chemical signal that makes the cell membrane of
the motor cells more permeable to potassium and
chloride ions. Movement of these ions out of the
motor cells causes water to leave the cells by
osmosis. The motor cells then collapse, causing
movement of the leaf or leaflet.
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www.srl.caltech.edu/.../ www/carniverous.html
Rapid movements in Carnivorous Plants Venus fly
trap - Two hinged lobes with three sensitive
hairs, these hairs set off an electrical impulse
that triggers the leaf to close. - An example of
acid growth, not turgor pressure. The
electrical impulses studied in plants are the
same, in principle, as the nerve impulses of
animals.
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Generalized Effects of Touch on Plant Growth
Touch and other mechanical stimuli may also have
widespread effects on patterns of growth.
Regular rubbing or bending of stems inhibits
their elongation and results in shorter, stockier
plants. This response also involves both
electrical signals and a change in the cell
membrane permeability.
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Chemical Communication Among Plants
GrrrIm a mean leaf-eating bug!
In some species, the production of compounds is
initiated or increased in response to damage
inflicted on the plant by herbivores. - ex
Chewing insects. Plants protect themselves as
well as warn neighboring plants of the same
species to mobilize their defenses prior to
attack. Studies currently in progress are
designed to isolate and identify the airborne
substance or substances involved in this
communication.
www.geocities.com/ wallpapercollection/page_01.htm

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THE END! Woohoo! Im done! Wasnt that great? I
think I smell an A! Dont you Ms. Walters?