Polyketide-derived alkaloids and anthraquinones in Aloe plants and cell cultures

Plants of the genus Aloe L are known to be rich in secondary metabolites such as anthraquinones and flavonoids. Only twelve out of about 400 species contain piperidine alkaloids. Representative species of this group, Aloe gariepensis Pillans, A. globuligemma Pole Evans and A. viguieri H. Perrier were cultivated in vitro and investigated for their polyketide-derived content using gas chromatography-mass spectrometry. All three species contained hemlock alkaloids in different amounts either in leaves or roots but A. globuligemma and A. viguieri accumulated N-methylconiine, an alkaloid not previously reported from any Aloe species. Micropropagation of A. viguieri was investigated using statistical experimental design. A mother plant produced up to five plantlets of good quality on Murashige and Skoog (MS) medium [1] with 0.25 mg L-1 6-Benzyl Aminopurine (BA) and 0.4 mg L-1 Naphthalene Acetic Acid (NAA). Calli of A. gariepensis and A. viguieri explants were induced on MS medium containing a combination of 10.0 mg L-1 NAA and 0.2 mg L-1 BA and 6.0 mg L-1 2,4-Dichlorophenoxyacetic acid (2,4-D), respectively. Long-term callus maintenance was facilitated on MS with 1.0 mg L-1 2,4-D for both species. The callus of neither species contained piperidine alkaloids after elicitation with chitosan or salicylic acid. After elicitation with chitosan or salicylic acid the suspension cultures of both Aloe species contained anthraquinones, chrysophanol and chrysarobin, the latter representing a new record for the genus.