Biosynthesis of monoterpenes and norisoprenoids in raspberry fruits (Rubus idaeus L.):: The role of cytosolic mevalonate and plastidial methylerythritol phosphate pathway

The biosynthesis of the monoterpenes (-)-alpha-pinene, linalool, and the norisoprenoids alpha- and P-ionone in raspberry fruits (rubus idaeus L.) was investigated by in vivo feeding experiments with [5,5-(2) H-2]mevalonic acid lactone and [5,5-(2) H-2]-1-deoxy-D-xylulose. The volatile compounds were extracted by stirbar sorptive extraction and analyzed using thermal desorption-multidimensional gas chromatography-mass spectrometry (TD-enantio-MDGC-MS). The feeding experiments demonstrate that (-)-alpha-pinene and (S)-linalool are exclusively synthesized via the cytosolic mevalonic acid pathway. In contrast, H-2-labeled (R)-(E)-alpha-ionone and H-2-labeled (E)-beta-ionone are detectable after application of d(2)-1-deoxy-D-xylulose and d(2)-mevalonic acid lactone, respectively. However, (R)-linalool reveals no incorporation of either one of the fed precursors, even though this enantiomer is detectable in the fruit tissue.