Saving the East Indian sandalwood tree

Plant cell cultures have yielded valuable natural products in the form of pharmaceuticals, flavours and fragrances, and agricultural, cosmetic, bioherbicidal and fine chemicals, with approximately 2000 new plant chemicals added annually. The global market for plant-derived drugs was worth an estimated US$18 billion in 2005, with an expected annual growth rate of 6.6% to US$26 billion by 2011.

The East Indian sandalwood tree, Santalum album, is a woody and tropical forest tree that belongs to the family Santalaceae. The species is globally acclaimed for its very costly heartwood and essential oil obtained from matured specimen trees. Unmet needs for use in perfumery (fragrance) and as food additives (flavour) have led to the decline of natural sandalwood populations due to illegal trade and harvesting and overexploitation. The estimated global annual requirement is ∼10,000 tons of wood (equivalent to 200 tons of oil), involving a trade of approximately US$125 million, of which only 10% is met from natural resources. A natural enemy in the form of the mycoplasmal ‘spike disease’ has placed the species on the IUCN Red List of Threatened Species.

Sandalwood also has extensive applications in traditional medicinal systems such as Ayurveda, and is gaining increasing importance in modern pharmacological investigations as a possible source of anticancer, anti-Helicobacter pylori and antiviral biomolecules. However, the havoc caused by the epidemic spike disease and the hemi-parasitic and slow-growing nature of the tree necessitated research towards the development of biotechnological means of in vitro production as early as 1963. A recent paper in AoB PLANTS describes a bioreactor-based production system as a biotechnological means of propagation for this endangered species.

Culture of East Indian sandalwood tree somatic embryos in air-lift bioreactors for production of santalols, phenolics and arabinogalactan proteins. (2013) AoB PLANTS 5: plt025 doi: 10.1093/aobpla/plt025
The East Indian sandalwood tree, Santalum album, yields one of the costliest heartwoods and precious essential oil. Unsurprisingly, this endangered forest species is severely affected due to unmet global demands, illegal trade and harvesting, overharvesting and an epidemic mycoplasmal spike disease. In vitro micropropagation endeavours have resulted in defined in vitro stages such as somatic embryos that are amenable to mass production in bioreactors. We report on somatic embryo production in a 10-L air-lift-type bioreactor, and compare the growth and biochemical parameters with those of a 2-L air-lift-type bioreactor. For the 10-L bioreactor with biomass (475.7 ± 18 g fresh weight; P < 0.01), concomitantly santalols (5.2 ± 0.15 mg L−1; P < 0.05), phenolics (31 ± 1.6 mg L−1) and arabinogalactan proteins (AGPs) (39 ± 3.1 mg L−1; P < 0.05) are produced in 28 days. In addition, we identified and quantified several santalols and phenolics by means of high-performance thin-layer chromatography and reverse-phase high-pressure liquid chromatography analyses, respectively. Results indicate that 10-L-capacity air-lift bioreactors are capable of supporting somatic embryo cultures, while the extracellular medium provides opportunities for production of industrial raw materials such as santalols, phenolics and AGPs. This will prove useful for further optimization and scale-up studies of plant-produced metabolites.