Figure 1.

The intermediates in the biosynthesis of prunasin and amygdalin in bitter almonds (A), with product formation in the tegument (B) and cotyledons (C) shown during fruit development. In the first reaction, Phe is converted to mandelonitrile by two CYPs belonging to the CYP79 and CYP71 families. The mandelonitrile is glucosylated by the previously known UGT85A19 enzyme (Franks et al., 2008). Amygdalin is glucosylated further by an unknown UGT. The enzymes identified in this study are shown on a gray background, whereas the previously described UGT85A19 is shown on a black background. Prunasin and amygdalin contents were analyzed by liquid chromatography-mass spectrometry (LC-MS) in tegument (B) and cotyledons (C) during fruit development (February to August, analyzed every second week), which represents the period from flowering to ripening (modified from Sánchez-Pérez et al. [2008]). FW, Fresh weight.