Analysis of storage proteins in normal and aborted seeds from embryo-lethal mutants of Arabidopsis thaliana.

The major storage proteins isolated from wild-type seeds of Arabidopsis thaliana (L.) Heynh., strain "Columbia", were studied by sucrose gradient centrifugation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Both the hypocotyl and cotyledons of mature embryos contained abundant 12 S (cruciferin) and 2 S (arabin) proteins that appeared similar in size and subunit composition to the cruciferin (12 S) and napin (1.7 S) seed-storage proteins of Brassica napus. The 12 S protein from Arabidopsis was resolved by SDS-PAGE into two groups of subunits with approximate relative molecular weights of 22-23 kDa (kilodalton) and 30-34 kDa. These polypeptides accumulated late in embryo development, disappeared early in germination, and were not detected in other vegetative or reproductive tissues. Accumulation of the 12 S proteins in aborted seeds from nine embryo-lethal mutants with different patterns of abnormal development was studied to determine the extent of cellular differentiation in arrested embryos from each mutant line. Abundant 12 S proteins were found in arrested embryos from two mutants with late lethal phases, but not in seven other mutants with lethal phases ranging from the globular to the cotyledon stages of embryo development. These results indicate that the accumulation of seed-storage proteins in wild-type embryos of Arabidopsis is closely tied to morphogenetic changes that occur during embryo development. Embryo-lethal mutants may therefore be useful in future studies on the developmental regulation of storage-protein synthesis.