| Studies were undertaken to identify the basis of differences in seed coat pigmentation between selected yellow- and brown-seeded Brassicaceae, and near-isogenic yellow- and brown-seeded lines of Brassica carinata (PGRC/E 21164). Histochemical analyses of dissected seed coats from six genera of the Brassicaceae revealed condensed tannin (proanthocyanidin) and phlobaphene pigments in dark-seeded species and in scattered spots in most yellow-seeded species. Anthoeyanins were not detected in any seed coat tissue of these species. In leaf tissue, anthocyanin content was lower in yellow-seeded B. carinata at the three- to four-leaf stage grown at 20 to 25°C, compared to similarly grown brown-seeded plants. At 15 to 18°C, both yellow- and brown-seeded lines produced similar amounts of anthocyanin in the seedling leaves.; In TLC and HPLC analyses, t-cinnamic acid, dihydromyricetin [trace amounts], dihydroquercetin, dihydrokaempferol and flavonols (quercetin, kaempferol) were more abundant in extracts from seed coats of yellow-seeded B. carinata than in extracts from seed coats of brown-seeded B. carinata. Myricetin was not detected in any seed coat extracts. Mass spectra were determined for phenylpropanoid and flavonoid aglycones from the seed coat extracts and for authentic standards.; Dihydroflavanol reductase (DFR) transcripts from developing seed were absent or less abundant at 5, 10, 20 and 30 days after pollination in the yellow-seeded line compared to the brown-seeded line of B. carinata. DFR transcripts in seedling leaves from the yellow-seeded line grown in warm, bright conditions were less abundant compared to similarly grown brown-seeded material. Seedlings grown at 15 to 18°C produced greater amounts of DFR transcript in both yellow- and brown-seeded lines of B. carinata compared to warm-grown plants.; Data from these experiments suggest that seed coat pigmentation in the Brassicaceae is due to condensed tannin and phlobaphene accumulation, not anthocyanins, and that seed coat pigment biosynthesis is down-regulated at dihydroflavonol reductase. The regulatory factor controlling DFR expression in developing seed may be temperature sensitive and also affect anthocyanin biosynthesis in seedlings and in related metabolic pathways: thioglycolic lignin concentration was significantly lower in the yellow-seeded Brassicaccae and in the seed coat tissue of yellow-seeded B. carinata compared to dark-seeded samples. |
