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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 1 6/5/2014 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 2 6/5/2014 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. 3 6/5/2014 Auxin Mode of Action - Recap Statolith Mode of Action - Recap Gravitropism Mode of Action Recap 4