Harmet, Kenneth H.
M.S. (Master of Science)
Department of Biological Sciences
The dhurrin and free amino compounds present in the coleoptiles and first leaves and the 1st internodes of 5 day and 7 day old dark-grown sorghum seedlings and 7 day old 1st internodes which had their coleoptiles and first leaves removed on day 5 were found to be different in the five groups. The 1st internode groups were found to have the same amount of dhurrin present but at a much lesser concentration than that in the coleoptiles and first leaves. The dhurrin decreased in the coleoptiles and first leaves from day 5 to day 7. The dhurrin content was measured by UV spectrophotometric analysis of the alcoholic extracts prepared from the various plant tissues. Paper chromatography of the alcoholic extracts was used to separate the free amino compounds and a 0.2 % ninhydrin spray was used to visualize the compounds on the chromatogram. The free amino compounds were seen to be similar amongst the five groups, except the day 5 decapitated group contained two additional compounds and contained more asparagine. The day 5 coleoptiles and first leaves also contained more asparagine than the other groups. The cyanogenic potential of the day 5 seedlings was determined for the coleoptiles and first leaves and for the 1st internodes. The potentials were determined by using Conway microdiffusion dishes to trap the cyanide released from the tissue and then the amount of cyanide released was determined by using the alkaline picrate test. An additional investigation was done using ¹⁴C-labeled seedlings grown from labeled seeds, and then recording the amount of ¹⁴C-labeled material in the 5 day and 8 day old seedlings. An alcoholic extract was prepared using the shoots from the 5 day old seedlings and another extract was prepared on day 8 using the 8 day old seedlings which had been excised from their seed and roots and placed in distilled water on day 5. A ¹⁴C-labeled dhurrin sample was prepared from each of the extracts by using paper chromatography to separate the dhurrin from the other components and then eluting the dhurrin from the chromatogram. The amount of ¹⁴C present was determined by recording the number of counts being emitted by using a liquid scintillation counter. The amount of dhurrin present in the extracts was then estimated by the number of counts recorded for the ¹⁴C present in the sample. The amount of ¹⁴C present in the plant tissue leftover from the extraction procedure and in the dried plant shoots was determined using the same methods as those for the extracts. It was found that the number of counts present in the ¹⁴C-dhurrin decreased from day 5 to day 8 while during the same period the number of counts in the extraction residue increased. Thus, it can be seen that the dhurrin is being metabolized. The dhurrin is rapidly being formed and transported to the epidermal vacuoles as a means of storing the excess nutrient materials being released from the seed. When the nutrients are exhausted the dhurrin is metabolized to form glucose, free amino compounds, and phenolic compounds.
Anderson, James A., "Distribution of dhurrin, cyanogenic potential and free amino compounds in dark-grown sorghum seedlings" (1981). Graduate Research Theses & Dissertations. 2267.
Northern Illinois University
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