Simultaneous induction of postabscission and germination mRNAs in cultured dicotyledonous embryos

Cloned mRNAs identify three programs of gene expression in cotton (Gossypium hirsutum L.) embryos that are associated with the maturation (reserve accumulation) stage, the postabscission stage, which is marked by expression of Late-embryogenesis-abundant (Lea) mRNAs, and germination (broadly defined as including all events through early postgerminative growth). In order to test if the regulation of these programs is the same in other dicotyledonous species, their expression was studied in normal and cultured maturation-stage, postabscission-stage, and mature embryo-stage embryos or seed of oilseed rape (Brassica napus L.), soybean (Glycine max [L.] Merr.), and tobacco (Nicotiana tabacum L.) using cotton and other cDNA probes. During postabscission, Lea mRNAs accumulated in all test species and were induced in earlier maturation-stage embryos by excision and culture on basal medium. Abscisic acid often enhanced this induction in the test species. Germination-specific mRNAs were induced in cultured maturation-stage and postabscission-stage embryos of all test species. These results indicate that the regulation of embryonic and germination programs is similar in all dicotyledons tested. Because excised embryos simultaneously induced postabscission and germination programs, the effects of exogenous growth regulators and other factors on such embryos probably reflect stress responses of germinating mature embryos rather than the identity of endogenous regulators of embryogenesis.