Histochemical characterisation of unextractable seed coat pigments and quantification of extractable lignin in the Brassicaceae

The differences determined by in situ histochemical staining and thioglycolic lignin analyses provided a new view of seed coat composition in a range of yellow- and brown-seeded germplasm of the Brassicaceae. Unextractable seed coat pigments were composed of proanthocyanidin (condensed tannin) polymers. Anthocyanins were absent in all seed coat tissues. Proanthocyanidin was deposited over the entire seed coat in dark-seeded germplasm and in patches in some yellow-seeded germplasm. The seed coat and hilum of Crambe abyssinica cv Prophet and some yellow-seeded accessions contained an unidentified, unreactive brown pigment. Several new pigmentation patterns, occurring as spots and patches and surrounding the hilum, became apparent from this analysis. Thioglycolic lignin was significantly lower in yellow-seeded samples compared with the dark-seeded accessions, and the majority of the lignin occurred in the seed coat. These discoveries provide new and useful data for plant breeders and indicate the need to use more detailed analytical methods in breeding programmes that have the goal of improving seed meal quality by reducing fibre and phenolics. (C) 2004 Society of Chemical Industry