The genus Picrasma contains about six species and belongs to the family Simaroubaceae. A wide variety of biologically active compounds have been isolated from members of this family, the majority of which are quassinoids. The wood from these trees has been used as a traditional medicine and lately some quassins have been reported to have important antileukemic properties ().
Picrasma quassioides (D. Don) Bennett, (Simaba quassioides D. Don; P. ailanthoides Planch.) is a lofty, deciduous tree whose distribution is reported throughout the tropics, with most commercial supplies being obtained from the West Indies. It does, however, also grow in more temperate regions (). The slender tree grows to 20-40 ft. and is characterized by its young bark, which is reddish-brown and marked with yellow spots. The glossy green leaves are pinnate, bearing several long, ovate leaflets, which turn to a dramatic scarlet color in the autumn ().
Picrasma quassioides, like some other simaroubaceous species, produce bitter drugs which have been used extensively in folk medicine. Quassia wood was originally derived from the bushy tree Quassia amara, but is now also harvested from Picrasma quassioides.
After felling, the trunk and main branches are logged, the bark removed and the wood chipped. These wood chips are then dried in kilns before being transported for chemical extraction (). The bitter principles of these trees form a family of compounds known as the quassinoids or simaroubolides ().
Quassia wood is still sometimes used as an enema in the treatment of threadworm and as a dusting powder to destroy lice and other parasites (). As an organic insecticide, it is effective against sawfly caterpillars and aphids (). Quassia wood is also commercially extracted to produce the bitter agent, quassin. Commercial supplies of quassin obtained in the United Kingdom have been shown to consist of the chemicals quassin, neoquassin and 18-hydroxyquassin (). Quassin is used as a foo4 flavouring agent, being 1670 times more bitter than caffeine and is used as a bittering agent in the soft drinks industry ().
Callus and suspension cultures have been successfully initiated and maintained from Picrasma quassioides (D. Don) Bennett. Callus was formed from germinating buds cultivated on Gamborgs B5 medium supplemented with 1 mg/l 2,4-D, 0.1 mg/l kinetin and 10% (v/v) coconut milk. Callus was in fact slow to develop, but after a few weeks in culture a soft friable callus was obtained. Despite this, suspension cultures proved to be difficult to maintain, as the cells were very sensitive to shear and tended to form large aggregates. These problems were alleviated by growing the cells in fluted flasks, which gradually reduced aggregate size, while shear sensitivity decreased with culture age. A large variety of growth conditions have been studied and a fast-growing, shear-resistant cell line has been obtained.
It is difficult to select the best form of explant, as only stem cuttings were available; seeds would perhaps be the best choice. The medium of choice for callus was B5 containing 10% coconut milk, 2% glucose, 1 mg/l 2,4-D, and 0.1 mg/l kinetin; and for the suspension cultures, B5 containing 2% glucose, 1 mg/l IB A and 0.5 mg/l IPAR. The conditions for growth of both callus and suspension were 25 °C, in subdued light, with shaking at 150 rpm for the suspension cultures. Quassin was detected in suspensions cultured in the above medium but only after sometime in culture, therefore it is difficult to specify a medium for quassin accumulation.
In addition to studies on growth and maintainance of the Picrasma quassioides cell line, investigations have involved methods for the extraction and detection of the sesquiterpenoid quassin from these tissue cultures. These methods are described and the cultures examined for quassin accumulation under the wide range of environmental conditions reported. Quassin, albeit at low concentrations, has been detected in suspension cultures growing in B5 medium containing 2% glucose, 1 mg/l indolebutyric acid and 0.5 mg/l N6 (A2 isopentyl) adenine riboside. This result offers the possibility for future selection of higher yielding cell lines which, combined with the fact that these cells can be easily grown in 3-1 continuously stirred tank bioreactor, promises some potential for the production of quassin from tissue culture systems.
Selections from the book: “Medicinal and Aromatic Plants IV”, 1993.