Immunolocalization of α-santalol in sandalwood
Alpha-santalol is a key constituent of sandalwood essential oil and is responsible for most of its biological activities. The heartwood of a mature East Indian sandalwood tree accumulates this sesquiterpenoid-rich oil. Although gas chromatography (GC) and GC–mass spectrometry (GC–MS)-based technologies are used to detect and quantify santalols from heartwoods and the essential oil, information on the sites of deposition of these molecules remains obscure. Recently, in vitro cells of sandalwood were shown to accumulate sandalwood oil constituents. However, no reports are available on the visualization of these small molecules in planta. Immunization of rabbits with a bovine serum albumin (BSA)–α-santalol conjugate resulted in the production of anti-α-santalol polyclonal antibody in six weeks, which showed high affinity and specificity. The success and extent of cross-linking of α-santalol with BSA was further confirmed by photometric, fluorometric and chromatographic methods. These polyclonal rabbit antibodies were used to immunolocalize α-santalol in sandalwood plant materials for the first time. Results indicate the localization of α-santalol to the vascular bundles of somatic embryos and leaves, whereas distribution was evident in secondary xylem, cortical parenchyma and epidermis of the mature stem. Furthermore, the polyclonal antibody is shown to be a useful tool in detection of both free and immobilized α-santalol for screening purposes.