Download Gravitropism

6/5/2014
Tropisms
Gravitropism &
Thigmotropism
Robell Abraha
Don Smith
Sabrina Libby
Overview
➢ Directional Plant growth responses
➢ Are permanent
➢ Plants can exhibit wide range of Tropisms:
○
○
○
○
○
Traumatropism - Wound
Hydrotropism - Water
Geomagnetotropism - Magnetic Fields
Gravitropism
Thigmatropism
Plants Response to
Gravity
➢ Auxins play primary role
➢ Four steps:
○ Gravity perceived by cell
○ Signal formation
○ Signal transduced intra- and intercellularly
○ Differential cell elongation
Gravitropism
● Also referred as Geotropism
● A plant’s growth response to
gravity.
● It can be positive gravitropism
or negative gravitropism.
● The concentration of the plant
hormone Auxin is key to the
direction of growth as well.
Positive Gravitropism VS Negative Gravitropism
Positive-Grows with the
directional force of gravity.
Negative
Negative-Grows away from
the force of gravity.
Typically roots grow into the
ground (positive
gravitropism) Stems and
leaves grow up above the
ground (negative
gravitropism)
Positive
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Where does Auxin fit
in?
In leaves elongated growth is promoted where higher
concentrations of Auxin are present. Auxin is located
on the lower surface of the leaf causing the leaf to Leaves
curve.
Roots
Root response to Gravity
In roots a higher concentration of
auxin will inhibit elongational
growth. Auxin in roots is uniformly
distributed causing the root to grow
evenly and straight down.
Root response to Gravity - Sensing
Without Root
Tip, No
Gravitropism
Root response to Gravity - Sensing
Statoliths
Starch filled Amyloplastic organelles
that are pulled to the lowest part
of the cell by gravity
Thigmotropism
•Contact with a solid object
changes the direction of plant
growth
•Involves TOUCH genes and
calcium ions
•Results in unequal growth rates
on opposite sides of the shoot
Starch filled Amyloplastic organelles that are pulled to the lowest part of the cell by
gravity
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Thigmotropis
m
Plants have a sense of touch?
● Some plants are much more sensitive to touch
than humans
o Some are 10 times more sensitive
Thighmonasty= Rapid plant movement, short
term stimuli causes the plant to respond
rapidly, but does NOT change the directional
growth of the plant like thigmotropism.
Plants have a sense of touch?
What parts of the plant respond to touch?
● Clearest example is the coiling that occurs in some
tendrils.
● General touch response in roots are negative.
o When a root “feels” an object, the root grows away
from the it. Allowing growth with the least amount of
resistance.
● Most tendrils grow toward the touch stimulus.
o Allows for the tendril to wrap around the object it is
in contact with
How do Tendrils Actually Curve?
● Able to curve by
employing a process
known as “ Differential
Growth” .
● this process involves the
stimulation of growth in
particular regions of the
tendril.
References
http://plantsinmotion.bio.indiana.edu/plantmotion/movements/tropism/gravitropism/sunflower/sunflowergravi.html
Cain, Michael L. "Fig. 33.4." Discover Biology. Sunderland, MA: Sinauer Associates, 2002. Print. 8.2.1 Gravitropism." About the
Textbook. N.p., n.d. Web. 22 May 2014.
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/A/Auxin.html
Hideyuki, Takahashi, Miyazawa Yutaka, and Fugii Nobuharu. "Hormonal Interactions during Root Tropic Growth:
Hydro Tropism versus Gravitropism." Plant Molecular Biology 69 (2009): 489-502. Print.
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Auxin Mode of Action - Recap
Statolith Mode of Action - Recap
Gravitropism Mode of Action Recap
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