Brassicaceae plants are disclosed that contain a mutation in a delta-12 fatty acid desaturase gene and that have altered fatty acid composition in seeds. In one embodiment, a Brassicaceae plant contains a mutation in a region having the conserved motif His-Xaa-Xaa-Xaa-His, found in delta-12 and delta-15 fatty acid desaturases. A preferred motif has the sequence His-Glu-Cys-Gly-His. A preferred mutation in this motif has the amino acid sequence His-Lys-Cys-Gly-His.