A micropropagation protocol for Aloe arborescens has been developed in order to maximize the multiplication index and to minimize the cycle length. Explants were sterilized in NaOCl and subcultured weekly to overcome the effects of released polyphenol that, otherwise, caused browning of the cut surface, tissue damage and death. In order to identify the combination of plant growth regulators giving a suitable multiplication index, five substrates having Murashige and Skoog salts as a basis and differing in the type and concentration of auxins and cytokinins were tested. Explants cultured on the substrate containing 1.0 mg l-1 α-Naphthaleneacetic acid and 2.0 mg l-1 6-benzylaminopurine showed abundant sprouting from their base and from axillary meristems. The mean multiplication index obtained with this substrate was about 3.5. For callus induction, only substrates combining an auxin and a cytokinin were effective; percentages of explants producing callus in dark culture conditions were higher than those obtained in the light. Biological effects of leaf extracts from micropropagated plants of A. arborescens on proliferation of the murine myeloma cell line P3X were evaluated. Preliminary results confirmed the presence of bioactive molecules and their activity in inhibiting cell proliferation; such activity was lower than that of analogous leaf extracts from three-year-old plants. © 2009 Società Botanica Italiana.

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