The Conversion of [14C]Cycloartenol and [14C]Lanosterol into Phytosterols by Cultures of Nicotiana tabacum

Tissue cultures of Nicotiana tabacum were treated with [14C]cyeloartenol and [14C]lanosterol, and the 4,4-dimethylsterol 4-methylsterol and phytosterol fractions were examined for radioactivity. In both cases activity was incorporated into the phytosterols. The distributions of radioactivity in the 4,4-dimethylsterols and 4-methylsterols were compared with those obtained by incorporation of [14C]acetic acid. It is concluded that cycloartenol is a true phytosterol precursor in the tissue cultures, whereas the possible role of lanosterol (not detectable in the cultures, even by isotopic dilution experiments) is not proven.