Fig. 2

Pie chart of metabolite classification and percentages in four varieties of maize kernels (a). The outer circles in the pie chart indicate the detected metabolite categories and the percentage, while the inner circles show the specific subcategories of metabolites contained in each major category metabolite. Metabolite accumulation pattern of maize kernels (b) and principal component analysis (c). In the heatmap, the colors marked with green and red were down- and up-accumulated in maize kernels, respectively. W represents white kernels, Y represents yellow kernels, R represents red–purple kernels, and P represents purple–black kernels