In the previous studies, a ninhydrin positive substance (NPS) was detected in culture filtrate from Czapek's solution containing amino acid in place of sodium nitrate on which a plant pathogenic fungus had been cultured.
In this study, modified Czapek's solution containing tryptophan in place of sodium nitrate was prepared, and sucrose, xylose, manitol, inositol, glucose, or fructose was used as a carbon sorce of the culture medium. Alternaria solani was inoculated in the medium.
The NPS was detected only in the culture filtrate containing sucrose as a carbon source of the medium, and the Rf value of the NPS on a TLC plate was equal to that of fructose. It was shown by the other experiments that the spot of fructose on the TLC plate was colored by spraying ninhydrin reagent, and the spot of NPS was colored by anisaldehyde reagent.
These experimental results strongly suggest the possibility that the NPS is fructose.