Identification of the precursor of DNJ biosynthesis. A) Mulberry tissues used for metabolite analysis. Callus cultured in vitro. B) DNJ and precursor in different tissues of mulberry. The n.d. indicates that the substance is not detected. DNJ isomer, a metabolite identical to the mass spectrum of DNJ. Data are presented as mean value and standard deviations of 3 independent biological replicates. Significance was analyzed with ANOVA (P < 0.05).