Effects of Mineral Salts, Initial pH and Precursors on Digitoxin Formation by Shoot-forming Cultures of Digitalis purpurea L. Grown in Liquid Media

Abstract

Shoot-forming cultures of Digitalis purpurea L. were grown in various modifications of Murashige-Skoog medium. The effects of CaCl₂, MgS0₄, FeS0₄ coupled with Na₂-EDTA, minor elements, initial pH of the medium, some organic solvents as precursor solvents, and precursors on their growth and digitoxin formation were investigated. Reduction of the basal CaCl₂ concentration by two-thirds promoted both digitoxin formation and shoot-differentiation while a threefold increase repressed these. Ca^{+ +} proved to be responsible for this phenomenon. A threefold increase in the MgS0₄ concentration improved digitoxin formation, Mg⁺⁺ being responsible for this improvement. The optimal concentration of FeS0₄ coupled with Na₂-EDTA was similar to that in the MS basal medium. A threefold increase in the concentration of either KI, Na₂Mo0₄ or CuS0₄ improved digitoxin formation, the optimal pH of the medium before autoclaving being 6. Among methanol, ethanol, propylene glycol, dimethyl sulfoxide and acetone as the precursor solvents, methanol and acetone were relatively the least inhibitive at 2%. Progesterone at 0.1 mg/100 ml medium improved the digitoxin content per flask to 180% of that of the control cultures, whereas no promotive effect from cholesterol was observed.