Influence of plant growth regulators on volatiles produced by in vitro grown shoots of Agastache rugosa (Fischer & C.A.Meyer) O. Kuntze

The composition of volatile organic compounds emitted by in vitro shoots of Agastache rugosa (Fischer & C.A. Meyer) O. Kuntze (Lamiaceae) was studied using headspace solid-phase microextraction-gas chromatography-mass spectrometry and compared to the those emitted by adult plants and in vitro-germinated seedlings. Shoot-tip explants were cultured on a solid MS medium supplemented with either 4.4 mu M 6-benzyladenine (BA), 9.3 mu M kinetin, or 0.45 mu M thidiazuron and with either 0.57 mu M indole-3-acetic acid (IAA) or 0.41 mu M picloram. Shoot proliferation was observed in all these treatments. The presence of these plant growth regulators in the culture medium significantly influenced the composition of volatiles as well as morphogenetic responses observed. The number and quality of regenerating shoots and frequency of axillary bud break were highest in medium containing the BA + IAA combination. Sixty-five compounds were identified in the headspace of the in vitro-produced material and plants cultivated in the field. The in vitro shoots emitted both hydrocarbon (limonene, alpha-pinene) and oxidized (menthone, isomenthone, pulegone) monoterpenes. The composition of monoterpenes differed depending on the type of auxin-rather than cytokinin-in the medium. The emission of phenylallyl compounds, such as estragole, a major compound in field-grown plants, was markedly lower in shoot cultures.