Abscisic acid-regulated responses of dormant and non-dormant embryos of Helianthus annuus: Role of ABA-inducible proteins

Embryos of Helianthus annuus L. became dormant 3 weeks after anthesis and their dormancy was lifted during storage in dry conditions. The objectives of this study were to investigate changes in the pattern of soluble proteins associated with the release of embryo dormancy. Sunflower dehydrins and group 3 late embryogenesis-abundant (LEA) proteins were studied in developing embryos. Three dehydrins (17, 21 and 26 kDa) and two group 3 LEA polypeptides (17 and 23 kDa) appeared during dormancy induction. Their levels remained steady until maturity. After imbibition, these polypeptides disappeared within 24 h except for the 23-kDa protein whose levels remained stable for a further 4 d, whatever the culture condition. Analysis of radiolabelled proteins by two-dimensional gel electrophoresis revealed that among dormancy-associated proteins other than dehydrin and group 3 LEA, several low molecular mass (18, 19, 20 and 21 kDa) proteins were expressed in dormant embryos but not detected in non-dormant embryos. After a treatment with fluridone, which inhibits ABA synthesis, or with GA3, which allows germination to occur, the 19-kDa protein could not be detected. In contrast, application of ABA to non-dormant embryos arrested germination and enhanced the synthesis of the 18- and 21-kDa proteins, but not that of the 19- and 20-kDa polypeptides. These results demonstrate that steady-state levels of specific proteins change during early imbibition of dormant and non-dormant sunflower embryos and indicate that these changes may be associated with differential gene expression responsible for the maintenance of dormancy.