Poster: Seed Biology

Abs # 547: Endo-b-mannanase activity and completion of embryogenesis in imbibed carrot (Daucus carota L.) seeds

Presenter:	Homrichhausen, Tanja M, hiro.nonogaki@oregonstate.edu
Authors	Homrichhausen, Tanja M (A)   Hewitt, Jessica R (B)   Nonogaki, Hiroyuki  (C)
Affiliations:	(A): Department of Chemical Engineering, Oregon State University (B): Department of Biochemistry and Biophysics, Oregon State University (C): Department of Crop and Soil Science, Oregon State University

A cDNA encoding an endo-b-mannanase (EC 3.2.1.78) from imbibed carrot (Daucus carota) seeds has been isolated and characterized. The full length cDNA (DcMAN1) exhibited a 64% and 59% deduced amino acid sequence identity with tomato (Lycopersicon esculentum) seed germination-specific (LeMAN2) and postgermination-specific (LeMAN1) endo-b-mannanase cDNAs, respectively. The DcMAN1 mRNA was expressed in imbibed carrot seeds before radicle emergence. The rudimentary embryo that is located at the micropylar region of a mature carrot seed elongates and reaches the lateral part of a seed during imbibition. The expression of DcMAN1 mRNA and the enzyme activity were first detected in the micropylar-half seed at early imbibitional stages and then, occurred in the lateral-half seed at later stages of imbibition. The timing of the appearance of endo-b-mannanase activity in the lateral-half seed corresponded to that of embryo development in the lateral-half seed. Abscisic acid (ABA) did not inhibit the enzyme activity and embryo development in seeds. The temporal and spatial patterns and hormonal regulation of DcMAN1 expression in carrot seeds were consistent with embryo development in seeds. The enzyme activity was detected mainly in the endosperm, suggesting that the endo-b-mannanase activity is involved in degradation of the endosperm. These results suggest that DcMAN1 expression is associated with enlargement of corrosion cavity in a carrot seed to make space for the growing embryo.