7. Chemical studies on the action of A.
The original isolation by Sando and coworkers of the flavonol isoquercitrin from brown (aa B Pl) plants and of the anthocyanin chrysanthemin from purple (A B Pl) plants has been interpreted to mean that the A gene acts by substituting an atom of hydrogen for one of oxygen in isoquercitrin. However, as reported elsewhere, a number of brown pigments distinct from isoquercitrin are present in the brown plant and are affected by A action; moreover, anthocyan pigments in addition to chrysanthemin are present in the purple plant, absent in the brown. Since isoquercitrin is not responsible for the brown phenotype of the aa B Pl plant it might be questioned whether this pigment is affected by the A gene. This point has been investigated by separation of the pigments by the paper chromatographic technic followed by spectrophotometric analysis. Spectral absorption curves characteristic for isoquercitrin have been obtained by this method from extracts of both purple (A B Pl) and brown (aa B Pl) plants. However, there is strong indication that more of this pigment is present in husks of brown than in those of purple plants. Hence it appears that the A gene does affect the amount of isoquercitrin present, but in view of the other pigments involved, it is by no means valid to conclude that the action of this gene is concerned with the step which makes the difference between isoquercitrin and chrysanthemin.