Studies on the Production of Digitalis Cardenolides by Plant Tissue Culture

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Abstract
Undifferentiated, highly chlorophyllous cell cultures, undifferentiated white cell cultures; green, shoot-forming cultures; and white, shoot-forming cultures of D. purpurea L. were established and subcultured every 3 wk in liquid media in the light or in the dark. The digitoxin content, the chlorophyll content and the ribulose bisphosphate carboxylase activity of these cultures were assayed. The light-grown, green shoot-forming cultures accumulated considerable amounts of digitoxin (.apprx. 20-40 .mu.g/g dry wt) and the white shoot-forming cultures without chloroplasts accumulated .apprx. 1/3 that amount of digitoxin. The chlorophyll content and the ribulose bisphosphate carboxylase activity of the undifferentiated green cells were about the same as they were in the green, shoot-forming cultures, but the digitoxin content of the former was extremely low (.apprx. 0.05-0.2 .mu.g/g dry wt), which is about the same as that in undifferentiated white cells without chloroplasts. Apparently, the chloroplasts are not essential for the synthesis of digitoxin in Digitalis cells. The optimum concentrations of the tested compounds for accumulation of digitoxin were: benzyladenine, 0.01-1 mg/l; IAA, 0.1-1 mg/l; .alpha.-naphthaleneacetic acid; 0.1 mg/l; and 2,4-D, 0.01 mg/l.