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Plant Physiology 63:1022-1028 (1979)
© 1979 American Society of Plant Biologists

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Articles

Tissue Distributions of Dhurrin and of Enzymes Involved in Its Metabolism in Leaves of Sorghum bicolor1

Mineo Kojima2, Jonathan E. Poulton, Susan S. Thayer and Eric E. Conn

a Department of Biochemistry and Biophysics, University of California, Davis, California 95616

The tissue distributions of dhurrin [p-hydroxy-(S)-mandelonitrile-beta-D-glucoside] and of enzymes involved in its metabolism have been investigated in leaf blades of light-grown Sorghum bicolor seedlings. Enzymic digestion of these leaves using cellulase has enabled preparations of epidermal and mesophyll protoplasts and bundle sheath strands to be isolated with only minor cross-contamination. Dhurrin was located entirely in the epidermal layers of the leaf blade, whereas the two enzymes responsible for its catabolism, namely dhurrin beta-glucosidase and hydroxynitrile lyase, resided almost exclusively in the mesophyll tissue. The final enzyme of dhurrin biosynthesis, uridine diphosphate glucose:p-hydroxymandelonitrile glucosyltransferase, was found in both mesophyll (32% of the total activity of the leaf blade) and epidermal (68%) tissues. The bundle sheath strands did not contain significant amounts of dhurrin or of these enzymes. It was concluded that the separation of dhurrin and its catabolic enzymes in different tissues prevents its large scale hydrolysis under normal physiological conditions. The well documented production of HCN (cyanogenesis), which occurs rapidly on crushing Sorghum leaves, would be expected to proceed when the contents of the ruptured epidermal and mesophyll cells are allowed to mix.

2 Permanent address: Institute for Biochemical Regulation, Faculty of Agriculture, Nagoya University, Chikusa, Nagoya 464 Japan.

1 This work was supported in part by National Science Foundation Grant PCM 77-25769 and National Institutes of Health Grant GM-05301-21.






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Copyright © 1979 by the American Society of Plant Biologists