Hairy roots of Atropa belladonna were cultured in a modified 2.5‐L multicompartment bubble column for analysis of growth kinetics, stoichiometry, and atropine production. Average biomass density reached 9.9 g L−1 dry weight after 43 days of batch culture; local root densities in some parts of the vessel were considerably higher, up to 17 g L−1. Bulk mixing in the reactor was very poor: after 14 days of culture, the time taken to reach 95% of the equilibrium value after a concentration pulse in the vessel was 12 min. Growth and specific sugar uptake rates declined continuously throughout the culture even though adequate sugar and nitrogen remained in the medium. The observed biomass yield from sugar was approximately constant at 0.35 g g−1; biomass yields from ammonia and nitrate were 0.44 and 0.35 g mmol−1, respectively. Specific atropine content in the roots varied from 4.1 mg g−1 dry weight at the beginning of the culture to 1.4 mg g−1 after 28 days; 35 mg or 14 mg L−1 atropine was produced over the 43‐day culture period. Biomass composition was represented by the elemental formula CH1.63O0.80N0.13, plus 9.8% (w/w) ash. A balanced stoichiometric equation was developed for hairy root growth; this indicated that 8.3% of carbon supplied to the culture was excreted into the medium as byproducts.

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Linum flavum hairy roots were initiated from leaf discs using Agrobacterium rhizogenes strains LBA9402 and TR105 though two other strains, 15834 and A4, were relatively ineffective for induction. Significant variation in coniferin accumulation was observed between hairy root lines originating from different L. flavum seedlings and/or A. rhizogenes strains. Coniferin reached 58 mg g-1 dry wt by culturing the roots in Linsmaier and Skoog (LS) medium with 2,4-dichlorophenoxyacetic acid and naphthaleneacetic acid as growth regulators.

Novel cross-species coculture systems using Linum flavum hairy roots and Podophyllum hexandrum cell suspensions were applied for in vitro production of podophyllotoxin. The hairy roots and suspensions were cocultured in Linsmaier and Skoog medium in dual shake flasks and dual bioreactors. In separate experiments, coniferin feeding was shown to be an effective strategy for increasing the accumulation of podophyllotoxin in P. hexandrum suspensions. Because roots of L. flavum are a natural source of coniferin, hairy roots of this species were used in coculture with P. hexandrum to provide an in situ supply of coniferin. Compared with P. hexandrum suspensions cultured alone in shake flasks or bioreactors, podophyllotoxin concentrations in cocultured P. hexandrum cells were increased by 240% and 72% in dual shake flask and dual bioreactor systems, respectively. The availability and stability of coniferin in the medium are the most likely factors limiting podophyllotoxin synthesis in coculture. Intensification of the coculture process is required to further improve total podophyllotoxin accumulation on a volumetric basis.

The suitability of conductivity measurement for monitoring growth in plant cell culture has been tested using suspended cells and genetically-transformed hairy roots of Atropa belladonna, and aggregated cells of Solanum aviculare. Other researchers have proposed that a constant ratio exists between increase in cell concentration (Ax) and decrease in medium conductivity (AC). In all cases studied in this work, Ax/AC was not constant over a wide range of cell densities tested in batch culture. With cell suspensions, Ax/AC decreased continuously during the growth phase from 3.4 to 2.5 g cm 1-1 mS-~. For the hairy roots, the ratio between Ax and AC varied by as much as 4-fold during growth. The relationship between conductivity and growth for S. aviculare aggregates was found to vary depending on inoculum density. No simple correlation between conductivity change and cell growth was apparent for the plant-cell systems studied.