Abstract
The incorporation of adenosine-8-(14)C into adenosine cyclic 3':5'-monophosphate in coleoptile-first leaf segments of Avena sativa L. was investigated. Homogenates of segments incubated in adenosine-8-(14)C for either 4 or 10 hours were partially purified by thin layer chromatography followed by paper electrophoresis. A radioactive fraction, less than 0.06% of the (14)C present in the original homogenate, migrated as adenosine cyclic 3':5'-monophosphate during electrophoresis. Upon treatment with cyclic nucleotide phosphodiesterase, however, less than 10% of this radioactive fraction appeared as 5'-AMP. Deamination with NaNO(2) as well as further chromatographical purification also suggested that only a small fraction of the (14)C in the partially purified samples could be in adenosine cyclic 3':5'-monophosphate. The data suggest that levels of this nucleotide can probably be no greater than 7 to 11 picomoles per gram of fresh weight in oat coleoptiles. Treatment of such coleoptiles with physiologically active concentrations of indoleacetic acid, furthermore, had no significant effect on the (14)C radioactivity in marker adenosine cyclic 3':5'-monophosphate-containing fractions at any stage of purification during several experiments.In a single experiment, no labeled guanosine cyclic 3':5'-monophosphate could be detected in oat coleoptile-first leaf segments incubated in guanosine-8-(14)C either with or without indoleacetic acid. These results do not support the hypothesis that a cyclic nucleotide mediates the action of indoleacetic acid on oat coleoptile extension.