EFFECTS OF AUXIN AND PHENOBARBITAL ON MORPHOGENESIS AND PRODUCTION OFDIGITOXIN IN DIGITALIS CALLUS

Pieces of callus obtained from seedlings of Digitalis purpurea were gr own on solid Murashige-Skoog's medium supplemented with 1 mg liter(-1) BA and 0.1 mg liter(-1) IAA or NAA, with or without phenobarbital (40 mg liter(-1)). The replacement of the natural auxin IAA by the synthe tic auxin NAA increased callus growth and inhibited organogenesis, whe reas the addition of phenobarbital had the opposite effect. Morphometr ic measurements revealed a high ratio of vacuole to cytoplasm (v/v) in callus cells. This ratio was affected by the different treatments in the same way as the fresh weight. The activity of mitochondrial cytoch rome P450scc (the enzyme that provides the precursor, pregnenolone, fo r the biosynthesis of cardenolide in foxglove plants) was detected in the relevant fraction of callus grown under all experimental condition s, and its activity was increased by the addition of phenobarbital. Th e different treatments tested increased the cardenolide content and qu antifiable amounts of digitoxin were detected in all callus tissues. I t is of special interest that phenobarbital added to the culture mediu m increased the accumulation of digitoxin. The mechanism affecting the development and production of cardenolide in callus tissues of D. pur purea by phenobarbital and the replacement of IAA by NAA is discussed.