EFFECTS OF ETHYLENE AND AMINOETHOXYVINYLGLYCINE ON CARDENOLIDE ACCUMULATION IN TISSUE-CULTURES OF DIGITALIS-LANATA

Cardenolide accumulation in tissue cultures of Digitalis lanata was increased by the ethylene biosynthesis inhibitor aminoethoxyvinylglycine (AVG) and decreased by the ethylene releasing substance ethephon. The stimulatory effect of AVG (0.5 mg L-1) was dependent on the stage of growth at which it was added to the culture. Increased cardenolide accumulation was achieved by early addition (day 0) for a light tolerant strain (S-1) and late addition (day 12-15) for a light sensitive strain (S-2). In strain S-2 the AVG-dependent increase in cardenolide accumulation was greatly enhanced by a high medium content of MnSO4. When grown in this medium the cardenolide accumulation in the tissue was 440 % of the control (without AVG). The effect of ethephon was similar in the two strains; 5 mg L-1 resulted in a reduction of the cardenolide accumulation to 40 % of the control in strain S-1 and 20 % of the control in strain S-2. Later addition or lower concentration was less inhibitory to cardenolide accumulation, growth and, in strain S-1, chlorophyll accumulation.