Storage Protein Synthesis during Oat (Avena sativa L.) Seed Development.

Oat (Avena sativa L.) seeds harvested at 2-day intervals from anthesis to maturity were tested for their ability to incorporate [(35)S]sulfate into protein. Incorporation of [(35)S]sulfate into TCA-insoluble material began 2 to 4 days postanthesis (DPA), reached a peak 14 to 16 DPA, and was barely detectable by 24 DPA. Incorporation of label into globulin was parallel to total protein accumulation, and averaged about 85% of the total protein synthesis. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of total protein extracted from developing seeds indicated that some polypeptides coinciding with the alpha and beta globulin subunits were present 2 to 4 DPA, but the full complement of globulin polypeptides was not present until 10 DPA. Immunoprecipitation of in vivo labeled seed extracts showed that globulin polypeptides and the 59 kilodalton precursor were present at early stages of development (4 DPA). Quantitation of dot blot analysis, using an oat globulin cDNA clone as a probe, indicated that one species of oat globulin mRNA was most abundant 15 DPA, which is during the peak time of storage protein synthesis.