Biosynthesis and Degradation of a Wheat Embryo Cytokinin-Binding Protein during Embryogenesis and Germination

The accumulation and degradation of a wheat (Triticum durum) embryo cytokinin-binding protein (CBF-1) was followed during embryo development and germination by its N(6)-benzyladenine (BA) binding activity and immunological reactivity (rocket immunoelectrophoresis and Western blotting). Both BA binding activity and CBF-1 appeared at 2 weeks post-anthesis and rose sharply between 2 to 4 weeks before leveling off to approximately 47 micrograms per embryo (9% of the soluble embryo protein at maturity). In vitro translation of polyadenylated RNA from 20-day-old embryos yielded a polypeptide which was immunoprecipitable with anti-CBF-1 IgG and migrated closely to the 54-kilodalton CBF-1 polypeptide on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Upon germination, both the amount of CBF-1 and BA binding activity dropped to low levels within 3 days. The data are discussed in relation to the possible role of CBF-1 as a regulator of cytokinin availability, and comparisons are drawn between the structural and biosynthetic similarities found between CBF-1 and the vicilin storage proteins of legumes. An improved method for isolating undegraded CBF-1 from whole seeds is also presented.