[Activation of thiamine biosynthesis in callus cultures of Nicotiana Tabacum in the light].

In darkness growth of callus tissues of Nicotiana tabacum var. "Samsun" depends on an exogenous supply of thiamine; without addition of thiamine growth decreases and after 4 to 5 passages of three weeks on a thiaminefree medium the tissues die. In contrast to this result, the same tissue has been cultivated on a thiamine-free medium in the light for more than 30 passages without loss in vigor.Bioassays of extracts from tissues grown in light show a synthesis of thiamine in the tissues, whereas in dark grown tissues the thiamine concentration falls to low levels. The effect of light on the synthesis of thiamine presumedly depends on photosynthesis. Blocking of photosynthesis with DCMU or 2,4-D leads to a decreasing growth rate and results finally in a complete arrest of growth as in darkness.