Date of Award:
Doctor of Philosophy (PhD)
Plants, Soils, and Climate
Department name when degree awarded
Plant Science Ecology
Frank B. Salisbury
Aminoethoxyvinyl glycine (AVG) and silver thiosulfate, antagonists of ethylene biosynthesis and action in plants, both delayed onset of leaf epinasty in Xanthium strumarium L. (cocklebur) plants rotated on horizontal clinostats. Xanthium plants mechanically stressed by continuous horizontal or vertical shaking, or continuous twisting back and forth, did not develop any significant epinasty, while plants inverted every 20 minutes (upside down half the time) did develop epinasty. From this it appears that clinostat-induced epinasty is a result of gravity compensation rather than mechanical stress.
Treatment of Xanthium, Lycopersicon esculentum Mill. (tomato), and Ricinus communis L. (castor bean) plants with inhibitors of ethylene biosynthesis, AVG and cobaltous ion, and inhibitors of ethylene action, silver ion and carbon dioxide, significantly delayed stem gravitropic response times. AVG and silver were dependably effective in delaying gravitropism, while carbon dioxide and cobalt were less effective.
Unilateral application of ethephon solution (1%) to the upper 10 centimeters of tomato stems, caused stems to deflect up to 80° toward the side of application after 24 hours on a clinostat, while unilateral application of indole-3-acetic acid in lanolin paste (1%) to tomato and cocklebur stems caused up to 250° and 200° bending respectively, away from the side of application after 24 hours on a clinostat.
Cocklebur stems that are restricted from bending after placing them horizontally store bending energy as seen from the springing upward that occurs when the stems are released (up to an average of 150° after 40 hours of restriction). Most of these stems also showed a stored stimulus of gravitropic bending, continuing to bend for several hours after release and being placed upright, before straightening.
Wheeler, Raymond M., "The Roles of Mechanical Stress and Ethylene in Clinostat-Induced Leaf Epinasty and Gravitropic Response of Dicot Shoots" (1981). All Graduate Theses and Dissertations. 7577.
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