The removal of calcium ions from Murashige and Skoog culture medium induced a marked increase in the accumulation of cardenolides in cell suspension cultures of Digitalis thapsi. Cell viability was not affected although growth was slightly reduced. Strontium ions could substitute for calcium in inhibiting cardenolide production, this effect of calcium being reversed by the addition of LaCl3 or ethyleneglycol-bis-(β-aminoethyl ether)-N,N'-tetraacetic acid. The results suggest that calcium, apart from its general effects on growth, may play a role in the regulation of cardenolide metabolism in a concentration dependent manner.
Cell suspension cultures of Digitalis thapsi were grown in Murashige and Skoog medium under continuous light. The effects of the absence of CaCl2, elevation of the MnSO4 concentration from 0.1 mM to 5 mM or the addition of 100 μM LiCl on their growth and digoxin production were investigated. The elimination of calcium reduced growth and viability of cultures but promoted digoxin formation. An increase of the MnSO4 concentration or the addition of LiCl resulted in higher digoxin content. Under such conditions growth was not affected.
The effect of calcium-deprivation on growth and the production of cardenolides in two undifferentiated cell lines of Digitalis thapsi maintained under three different light regimes (16 h photoperiod, darkness, or continuous light) was investigated. Growth was stimulated by continuous light in both cell lines cultured in complete medium. The light regime did not affect cardenolide accumulation in the cells of the hypocotyl-derived line; by contrast, continuous light or darkness increased the production in the leaf-derived line. The elimination of calcium favoured cardenolide production independently of the origin of the suspensions and the light regime, this beneficial effect being predominantly manifested under continuous light.
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