Tissue Level Compartmentation of (R)-Amygdalin and Amygdalin Hydrolase Prevents Large-Scale Cyanogenesis in Undamaged Prunus Seeds

Abstract

Plum (Prunus domestica) seeds, which contain the cyanogenic diglucoside (R)-amygdalin and lesser amounts of the corresponding monoglucoside (R)-prunasin, release the respiratory toxin HCN upon tissue disruption. Amygdalin hydrolase (AH) and prunasin hydrolase (PH), two specific [beta]-glucosidases responsible for hydrolysis of these glucosides, were purified to near homogeneity by concanavalin A-Sepharose 4B and carboxymethyl-cellulose chromatography. Both proteins appear as polypeptides with molecular masses of 60 kD upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis, but they exhibit different isoelectric points (PH, 5.6-6.0; AH, 7.8-8.2). AH and PH were localized within mature plum seeds by tissue printing, histochemistry, and silver-enhanced immunogold labeling. As was previously shown in black cherry (Prunus serotina) seeds (E.Swain, C.P. Li, J.E. Poulton [1992] Plant Physiol 100: 291-300), AH and PH are restricted to protein bodies of specific procambial cells and are absent from the cotyledonary parenchyma, bundle sheath, and endosperm cells. In contrast, the cyanogenic glycosides in both plum and black cherry seeds, which were detected by tissue printing, occur solely in the cotyledonary parenchyma and are absent from the procambium and endosperm. It is concluded that tissue level compartmentation prevents large-scale cyanoglycoside hydrolysis in intact Prunus seeds.