Publication Date


Document Type


First Advisor

Kresheck, Gordon C.

Degree Name

M.S. (Master of Science)

Legacy Department

Department of Chemistry


Oats; Growth (Plants)


Oat coleoptiles grow by cell elongation rather than cell division. Indole-3-acetic acid is the auxin which controls this process. Results presented here demonstrate that reproducible enthalpy changes in the oat coleoptile system can be measured under standard conditions in an adiabatic solution calorimeter. The effects of varying the auxin concentration and the pH of the buffer on the rates of elongation and heat production have been studied. The ratio of the rate of elongation to the amount of heat produced in a given amount of time has been designated the caloric efficiency of elongation (CEE). Experiments in which the rates of elongation and heat production were monitored as the pH of the buffer solution was varied between 8.5 and 3.0 showed that acidic solutions gave increased rates of elongation, except at pH 3.0, where tissue turgor was lost. No measurable change in the rate of heat production was noted at any pH. No statistically significant changes were noted in the CEE. A four-hour treatment of the segments with N₂ at pH 4.5 was seen to cause tissue shrinkage, and a decrease in heat production and CEE. At pH 6.5 with two minutes of N₂ treatment, an increase in heat production was observed, while no change in the rate of elongation was seen. No statistically significant change in the CEE occurred. At pH 4.5 with 10⁻² M IAA, decreases in the rates of elongation and heat production were seen, and the CEE also decreased. At pH 6.5 with 10⁻² M IAA, an increase in the rate of elongation was observed, while the heat production decreased. This resulted in an increased CEE. At pH 6.5, with IAA concentrations between 10⁻⁷ M and 10⁻³ M, increases in both rate of elongation and rate of heat production were seen. The CEE also increased. Similar increases in the rate of elongation, the rate of heat production, and the CEE, at pH 4.5 with 10⁻⁵ M IAA were observed. The heat production at this optimal concentration (10⁻⁵ M IAA) at both pH values was approximately 1.5 cal/g-hr. When coleoptile segments were pre-soaked, loaded into the calorimeter vessel, and allowed to equilibrate before changing the buffer solution by adding 10⁻⁵ IAA, an increase in the rate of elongation proportional to the amount of time the segments were left in the auxin solution was observed; however, no detectable change in the rate of heat production occurred. Results of this study are consistent with previous work which suggested that the cell wall is resistant to penetration by protons from outside, and that the intracellular pH is not altered by varying the extracellular pH. They also support the hypothesis that the active form of the auxin is the protonated form, and that acidic solutions have an auxin-like effect on the rate of elongation. These results also provide evidence that exothermic processes are not coupled directly with the mechanism of cell wall elongation, because the percentage increase or decrease in heat production is not equal to that observed for segment elongation in any case.


Includes bibliographical references.||Includes illustrations.


viii, 76 pages




Northern Illinois University

Rights Statement

In Copyright

Rights Statement 2

NIU theses are protected by copyright. They may be viewed from Huskie Commons for any purpose, but reproduction or distribution in any format is prohibited without the written permission of the authors.

Media Type