Abstract
Summary Development of embryoid stage-1-globules in cultures of Digitalis lanata strain VII was inhibited by high density growth (2,500 globules ml -1 )- in a nutrient medium (Nm V-M) containing 5 μmol 1 -1 benzyladenine and 0.05 μmol 1 -1 naphthalene acetic acid. The slow growth of the globules in this medium (doubling time ca. 6 weeks) was brought about by daughter globule formation (adventive embryo-genesis). Dilution of the suspension to ca. 30 globules ml -1 by a nutrient medium (Nm VII-M) containing 5 μmol l -1 benzyladenine resulted in the synchronized development of the stage-I-globules to stage-II-globules and late bipolar embryo structures. Upon irradiation synthesis and accumulation of chlorophylls and cardenolides started in a programmed manner. Compared with somatic embryos grown de novo from parenchyma-like cells those obtained from synchronized stage- I-globules showed a reduced heterogeneity of the cardenolide content and an increased mean cardenolide level. Under optimum conditions (refeeding of phosphate) the mean cardenolide accumulation was > 1 μmol digitoxin equivalents g -1 dry wt (≙ ca. 8 μmol digitoxin equivalents 1 -1 culture) within a cultivation period of 30 days.
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