抄録
Growth of tobacco (Nicotiana tabacuum var. Bright Yellow) callus depended on an exogenous supply of thiamine or its phosphate lester in a culture medium. The growth was found maximum at the concentration of 10^<-6>M of the vitamin in the medium, above the concentration, however the growth was slightly retarded. Oxythiamine (5-(2-hydroxyethyl)-3-[(4-hydroxy-2-methyl-5-pyrimidinyl) methyl]-4-methylthiazolium chloride) and deaminothiamine (5-(2-hydroxyethyl)-3-[(2-methyl-5-pyrimidinyl) methyl]-4-methylthiazolium perchlorate) inhibited the growth of the callus cultured in the medium containing a limited amount of thiamine, and the inhibitory effect of these compounds was competed by a further supplementation of thiamine which could recover a normal growth. A mixture of pyrimidine (2-methyl-4-amino-5-hydroxymethylpyrimidine) and thiazole (4-methyl-5-β-hydroxyethylthiazole) moieties of thiamine was revealed to satisfy fully the requirement, the growth of the callus being associated with a significant increase in the contents of thiamine in the cells. In the absence of the thiazole, the pyrimidine did not show any significant growth effect. On the other hand, the thiazole alone could support the growth of the callus which was preliminarily cultured for 17 days in the thiaminedeficient medium. These results lead to the suggestion that thiamine is synthesized in vivo from the pyrimidine and the thiazole moieties in the tobacco callus as well as in plants and in microorganisms, and that the biosynthetic pathway of the thiazole is defective in the callus cells.
