Sequential steps for developmental arrest in Arabidopsis seeds

The continuous growth of the plant embryo is interrupted during the seed ma turation processes which results in a dormant seed, The embryo continues de velopment after germination when it grows into a seedling. The embryo growt h phase starts after morphogenesis and ends when the embryo fills the seed sac, Very little is known about the processes regulating this phase. We des cribe mutants that affect embryo growth in two sequential developmental sta ges. Firstly, embryo growth arrest is regulated by the FUS3/LEC type genes, as mutations in these genes cause a continuation of growth in immature emb ryos. Secondly, a later stage of embryo dormancy is regulated by ABI3 and a bscisic acid; abi3 and aba1 mutants exhibit premature germination only afte r embryos mature, Mutations affecting both developmental stages result in a n additive phenotype and double mutants are highly viviparous, Embryo growt h arrest is regulated by cell division activities in both the embryo and th e endosperm, which are gradually switched off at the mature embryo stage. I n the fus3/lec mutants, however, cell division in both the embryo and endos perm is not arrested, but rather is prolonged throughout seed maturation. F urthermore ectopic cell division occurs in seedlings. Our results indicate that seed dormancy is secured via at least two sequential developmental pro cesses: embryo growth arrest, which is regulated by cell division and embry o dormancy.