In vitro root differentiation and essential-oil accumulation in Angelica archangelica

We studied the relationship between root differentiation and the accumulation of essential oils in Angelica archangelica in in vitro cultures and in the intact plant., Root regeneration was obtained using stem and leaf explants subjected to treatment with the auxins indole-3-butyric acid, indole-3-acetic acid and alpha -naphthaleneacetic acid. In both stem and leaf explants, treatment with indole-3-butyric acid induced the highest rhizogenic response in terms of both percentage of explants with roots and number of roots per explant. Independently of hormonal treatment, stem explants produced a higher average number of roots per explant. Root meristemoids were already visible at day 7 of culture in the treatments with indole-3-butyric acid and indole-3-acetic acid; they were formed directly by cambial-cell division. In vitro-regenerated roots retained primary root structure and differentiated only two primary ephemeral ducts in the pericycle; no accumulation of essential oils was detected. Same-size roots taken from the intact plant showed secondary structure and essential-oil accumulation. The results of this study suggest that the synthesis and accumulation of essential oils in Angelica archangelica is closely linked to the differentiation of secondary secretory ducts.