LONG-TERM STORAGE IN LIQUID-NITROGEN OF AN EMBRYOGENIC CELL STRAIN OF DIGITALIS-LANATA

Cells of the cardenolide-forming embryogenic strain VII of D. lanata were stored in liquid N2 for about 3 yr without loss of viability. The cells were pregrown in a nutrient solution containing 3% mannitol, then equilibrated with a mixture of 10% sucrose and 10% glycerol as cryoprotectors, slowly cooled (0.5.degree. C min) till -100.degree. C in sealed glass ampoules, which were transferred to and stored in liquid N2. For recultivation the ampoules were warmed rapidly in a water bath. The cells were grown for 1 wk on a solidified medium and then cultivated as suspension. The cells used for cryopreservation and the recultivated cells showed the same growth rate, DNA content, rate of the glucosylation of added digitoxin and embryogenic capacity. The embryoid structures formed had the same ability to cardenolide biosynthesis and plant regeneration.