IMMUNOCYTOLOGICAL LOCALIZATION OF HYDROXYNITRILE LYASES FROM SORGHUM-BICOLOR L AND LINUM-USITATISSIMUM L

In cyanogenic plants the release of HCN is due to catabolism of cyanog enic glycosides by the sequential action of specific beta-glucosidases and hydroxynitrile lyases. It is generally assumed that intact cyanog enic plants prevent suicidal release of HCN by compartmentation of sub strate and catabolizing enzymes. To investigate this assumption, tissu e and subcellular localization of the hydroxynitrile lyases were deter mined in Sorghum bicolor L. and Linum usitatissimum L. using immunocyt ological techniques. These studies revealed that the highest detection level of hydroxynitrile lyase in both species was in the cytoplasm wi th lower levels in organelles. Furthermore, the enzymes are restricted to the cotyledons (Linum, Sorghum) and leaves (Sorghum), respectively . Enzymes were not detected in the cell wall or the vacuole where, in the case of sorghum, the appropriate cyanogenic substrate for the P-gl ucosidase is located. In neither plant could a compartmentation at the cellular level be found as hydroxynitrile lyase could be detected in mesophyll as well as in epidermal and bundle sheath cells, These obser vations confirm that suicidal release of HCN in sorghum as well as in linum is prevented by the separate compartmentation of enzyme and subs trate on the subcellular level.