Metabolomic Analysis of Low Phytic Acid Maize Kernels

Phytic acid, or hexaphosphorylated myo-inositol, is the major storage form of phosphorous (P) in maize kernels. Phytic acid in foods or animal feeds can complex with proteins and mineral cations resulting in reduced bioavailablility of important nutrients. Classic mutation breeding has been used to develop maize plants that produce kernels with significantly less phytic acid. An extensive survey of the low phytate phenotype in different maize genetic backgrounds grown in five field locations revealed that an increase in inorganic P correlated with a decrease in phytic acid P, but the increased amount of inorganic P did not consistently account for the P reduction noted in the low phytate lines. There were no quantitative phosphorous differences in phospholipids or starch. In follow-up experiments using a metabolomics approach, both mutant and wild type kernels were obtained from a single segregating ear, minimizing variability. Individual mature kernels were lyophilized and ground. Kernel phenotype was determined by using a simple colorimetric test for inorganic P content. Kernels of similar phenotype were pooled and extracted in aqueous methanol and partitioned into polar and and raw data was processed using the Leco ChromaTof peak deconvolution software. Compounds were identified via coelution and/or mass spectrum matching with authentic standards. Each of these metabolites was semi- quantified by calculating the ratio of the peak area of a characteristic extracted ion against that of the internal standard and correcting for sample weight. P-containing metabolites were recognized easily by a prominent m/z 299. Several P-containing metabolites were more abundant in low phytic acid kernels, although it is unlikely that they are responsible for the reduced yield associated with this phenotype.