Subcellular Localization of the Cyanogenic Glucoside of Sorghum by Autoradiography

The use of microautoradiography at the electron microscopic level indicates that the vacuole is the site of accumulation of the cyanogenic glucoside of Sorghum bicolor. When a specific biosynthetic precursor of dhurrin, p-hydroxy[3,5-(3)H]phenylacetaldoxime, was used, 90% of the tritium label was recovered in the vacuoles of tissue prepared for microautoradiography. l-[3,5-(3)H]Tyrosine and d-[1-(3)H(N)]glucose, nonspecific precursors of dhurrin, of differing solubilities and biosynthetic capacity, were also fed to the shoots. The data obtained from these controls indicated that the high recovery of label in the vacuole of aldoxime-fed shoots was not indicative simply of the size of the vacuole, nor was it a result of movement of labeled compounds during preparation of the tissue for electron microscopy. The problem of movement of these labeled compounds during dehydration of tissue was dramatically reduced by chemical dehydration in 2,2-dimethoxypropane in less than 30 minutes rather than with routine dehydration in acetone or alcohol series for 24 hours.