ULTRASTRUCTURE OF DIGITALIS-LANATA TISSUE-CULTURES - EFFECT OF GIBBERELLIC-ACID AND SAN 9789

The anatomy of two Digitalis lanata tissue culture strains, S-1 and S-2, has been studied. The cardenolide accumulating cell aggregates consisted of highly vacuolated cells with very lobed nuclei in the periphery and a central part of meristematic cells. Sieve tube elements and companion cells and tracheids were observed in some of the cultures. The effect of gibberellic acid (GA3) and SAN 9789 on the ultrastructure of the cultures was most apparent as regards the plastids and the amounts of mitochondria and ER. The content of starch seemed to be highest in the cardenolide accumulating strain S-2 grown in darkness (S-2D) with or without GA3, but considerable amounts were also found in S-1 grown in darkness (S-1 D) with or without GA3, which did not accumulate cardenolides. The amount of plastoglobuli was increased in S-1 by SAN treatment. It was also higher in S-2 D and S-2 D + GA3 than in S-1 D and S-1 D + GA3; i.e., it was high in tissues with blocked carotene synthesis. Many large plastoglobuli were also observed in apparently degenerating cells. The amount of ER seemed relatively high in cardenolide producing cultures. The amount of mitochondria was highly variable, but no correlation with cardenolide accumulation could be found.